CN102495935B - Determination method for risk of storage medium leakage of underground natural gas storage reservoir - Google Patents

Abstract

The invention provides a determination method for risk of storage medium leakage of an underground natural gas storage reservoir. The method is used for determining the risk of storage medium leakage of the underground natural gas storage reservoir based on a fuzzy fault tree so as to judge the possibility of leakage failure of the underground natural gas storage reservoir. In the method, the fault tree for the storage medium leakage from a salt cavern underground natural gas storage reservoir to the outside atmospheric environment is established, the probability of basic event causing the storage medium leakage to the outside atmospheric environment is determined by a historical data statistical method and an established engineering evaluation model, influence of various risk factors on the probability of basic event is introduced into the calculation of the probability of basic event in the form of correction factors, and simultaneously, according to the principle of controlling the leakage mode by a main event, and the fault tree logic, the determination methods for the risk of small-leakage mode, big-leakage mode and cracking mode storage medium leakage of the salt cavern underground natural gas storage reservoirs are established.

Description

A kind of assay method of risk of storage medium leakage of underground natural gas storage reservoir

Technical field

The present invention relates to a kind of assay method of risk of storage medium leakage of underground natural gas storage reservoir, particularly a kind of based on fault tree the assay method to cave type underground natural gas storage storage medium risk of leakage.

Background technology

Current China is many salt cave type underground natural gas storages of planning construction, the transfering natural gas from the west to the east one line matching construction Jintan gas storage in construction, and existing 5 old chambeies enter note and adopt the operation phase, during " 12 ", will reach the scale in 62 single chambeies; Tafelberg, the second west to east gas pipeline project matching construction Henan, Hubei cloud answer the projects such as salt hole air reserved storeroom also will during " 12 ", build.How to adopt an effective measure, reduce the impact of various hazard factor on underground natural gas storage safety, avoid underground natural gas storage accident to occur, effectively preventive maintenance is carried out in underground natural gas storage, accomplish pre-control in advance, become the major issue that China gas storage supvr faces.

Salt cave type underground natural gas storage is at present one of main natural gas storing mode and means in the world, in the emergency peak regulation of rock gas, can play a key effect.Yet, in the operational process of underground natural gas storage, may be subject to the harmful effect of the hazard factor such as burn into equipment failure, erosion, hydrate generation, mechanical damage, disaster, maloperation, Creep of Salt, cause gas storage stability and safe reliability to reduce, even cause catastrophic accident, as Leakage Gas, the inefficacy of molten chamber and reservoir area subsidence etc.According to statistics: underground natural gas storage, salt cave occurred repeatedly in the operation phase, safety and environment have been produced to huge devastating impact; Accident pattern mainly comprises leaks and injectivity and productivity decline two classes, wherein leakage accident accounting example maximum.Therefore, the safety problem of underground natural gas storage can not be ignored.

How to adopt an effective measure, reduce the impact of various hazard factor on underground natural gas storage safety, avoid underground natural gas storage accident to occur, effectively preventive maintenance is carried out in underground natural gas storage, accomplish pre-control in advance, become the major issue that gas storage supvr faces.Underground natural gas storage, salt cave risk assessment technology is the effective technology means that address this problem, its objective is and systematically identify the salt cave risk factors of underground natural gas storage operation phase, possibility size and severity of consequence that estimation risk factors have a negative impact to personnel, property or environment, and underground natural gas storage, definite salt cave risk level, control risk targetedly taking, the generation of preventing accident, guarantees its safety and steady operation.About the research of salt cave underground natural gas storage risk assessment, report seldom both at home and abroad, the underground natural gas storage risk assessment of salt cave there is no according to complying with.The underground natural gas storage risk assessment of salt cave is the result of comprehensive underground natural gas storage failure probability and consequences analysis, determines the process of its risk level.The assay method of underground natural gas storage, salt cave risk of leakage is one of key point of setting up underground natural gas storage, salt cave risk assessment technology, significant for the leakage accident generation of prevention gas storage and lifting China underground natural gas storage safety management level.Therefore the assay method of, studying effective underground natural gas storage risk of leakage is particularly urgently with important.

Summary of the invention

The present invention aims to provide the assay method of a kind of salt cave type underground natural gas storage storage medium risk of leakage, be used for judging that leakage failure possibility occurs in underground natural gas storage, for underground gas storage risk assessment provides failure probability data, the present invention can solve the problem of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave, for prevention underground natural gas storage, salt cave leakage accident provides technological means, thereby guarantee the safety and steady operation of underground natural gas storage, salt cave.

An assay method for risk of storage medium leakage of underground natural gas storage reservoir, the method based on fuzzy fault tree is measured risk of storage medium leakage of underground natural gas storage reservoir.

Concrete technical scheme is realized by following steps:

An assay method for risk of storage medium leakage of underground natural gas storage reservoir, comprises the steps:

A obtains the data information of underground natural gas storage, salt to be evaluated cave;

The data information of B based on underground natural gas storage, described salt cave, identification causes the risk factors that storage medium leaks;

C is usingd and is leaked into atmosphere event as top event, determine secondary event, elementary event and cause the cut set of top event successively, sets up fault tree;

D determines the relation of described elementary event and described risk factors;

Data information and the engineering judgment model of E based on underground natural gas storage, described salt cave, calculates described risk factors and causes the elementary event probability of happening being associated;

F determines that described risk factors cause that different leakage mode leak into the probability distribution that atmosphere occurs;

Described in G basis, cause top event cut set, described in determining, cause in top event cut set and cause and leak into the part of taking charge that atmosphere event occurs;

H distributes according to described elementary event probability of happening and described risk factors leakage probability, the probability of happening of the part of taking charge described in determining and described in cause the probability of happening of the cut set of top event;

I according to described in take charge probability of happening and the described fault tree of part, calculate the probability of happening of described secondary event under described top event;

J, according to the probability of happening of described step fault tree and described secondary event, calculates the probability of happening of described top event under described different leakage mode;

Wherein, the model of engineering judgment described in step e comprises that erosion CALCULATION OF FAILURE PROBABILITY model, casing corrosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause casing leak and salt cave top board leakage probability computation model and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model, wherein, described erosion CALCULATION OF FAILURE PROBABILITY model is as the formula (1):

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\×\mathrm{ratio}=2.572\×{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\×\mathrm{ratio}---\left(1\right)$

E wherein_kfor erosion rate, unit is times/year; W is sand flow velocity, and unit is Kg/day; V is flow rate, and unit is m/s; D is pipe diameter, and unit is mm; S_kfor geometric shape parameters, Pf_erosionfor erosion causes the probability of equipment failure, unit, be times/year; T is equipment wall thickness, and unit is mm; Ratio is that gas storage accounts for year ratio with throughput rate operation in maximum day.

Preferably, the data information of the underground natural gas storage, salt described to be evaluated cave in described steps A comprises salt cave underground gas storage library information, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor, maintenance and/or maintenance history data.

Preferably, underground natural gas storage, the salt cave information in described steps A comprises gas storage title, gas storage type, evaluates salt cave well numbering, salt cave well designed life and salt cave well active time.

Preferably, the storage medium characterisitic parameter in described steps A comprises the Dynamic Viscosity of storage medium type, gas constant, rock gas molecular weight, rock gas relative density and rock gas.

Preferably, the salt cave well geometric shape parameters in described steps A comprises salt cave volume, storage capacity, work tolerance, cushion steam amount and tubing string size.

Preferably, the operational factor in described steps A comprises the maximum operating pressure of well head, the minimum operating pressure of well head, salt cave maximum design pressure, salt cave minimal design pressure, salt cave temperature, injecting gas temperature and peak performance.

Preferably, the maintenance in described steps A and/or maintenance history comprise the incident of leakage having occurred, the salt cave unstability event and the maintenance history that have occurred.

Preferably, the risk factors in described step B classify as that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force six classes.

Preferably, in described step C, by well head facility, leak and be described secondary event by the underground ground that leaks into.

Preferably, describedly by well head facility, leak and to comprise that emergency shut-in valve leaks, above tubing hanger, below well head leakage, packer leakage, tubing leak and tubing hanger, well head leaks.

Preferably, described by undergroundly leaking into that ground comprises that packer leaks, leak path, the leakage of salt cave top board, cap rock leakage, casing leak to ground, by production casing cement mantle, leak and leak by surface string cement mantle.

Preferably, the cut set that causes top event described in step C comprises 6 cut sets, be followed successively by cutset 1 for emergency shut-in valve leakage, cut set 2 is that above tubing hanger, well head leaks, cutset 3 is that well head leaks below packer leakage, tubing leak and tubing hanger, cutset 4 is the leak path to ground, the leakage of salt cave top board and cap rock leakage, cutset 5 is for packer leakage, casing leak, leaked and leaked by surface string cement mantle by production casing cement mantle, and cutset 6 is for to be leaked and to be leaked by surface string cement mantle by production casing cement mantle.

Preferably, described casing corrosion CALCULATION OF FAILURE PROBABILITY model is to increase based on the theoretical definite corrosion default of stress-strength Interference the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, as the formula (2).

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}<0}}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{SMTS}\right)\mathrm{dP}---\left(2\right)$

This model adopts Monte Carlo method to calculate, wherein, and Pf_burstfor casing corrosion failure probability, unit is times/year, and f (d, L, t, D, SMTS, P) is variable d, L, and t, D, SMTS, the joint probability density function of P, D is sleeve pipe external diameter, unit is mm, the thickness that d is etch pit, unit is mm; T is wall thickness, and unit is mm; L is the effective length of wall thickness loss, and unit is mm; P is effectively interior pressure, and unit is kPa, the tensile strength that SMTS is material, and unit is kPa, LSF_burstfor limit state function, it is that explosion occurs while surpassing the burst pressure of prediction operating pressure that corrosion default increases the ultimate limit state cause the explosion of residue tube wall; Limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF_burst＝P_burst-P_op

（3）

As LSF > 0; LSF=0 and LSF<0 represent respectively safety, the limit and failure state;

$P_{\mathrm{burst}}={\mathrm{\&sigma;}}_{\mathrm{flow}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]---\left(4\right)$

σ_flow＝SMTS

（5）

$M={[1+\frac{0.8L^2}{\mathrm{Dt}}]}^{1/2}---\left(6\right)$

P wherein_burstfor prediction failure stress, unit is kPa;

for flow stress, unit is kPa; M is Folia coefficient; A is the area of metal loss,

a₀for original area, i.e. L * t, unit is mm^2,sMTS is the tensile strength of shell material, and unit is kPa; P_opin effectively clean, press, first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as overpressure, and subtract each other with pipe external pressure, take absolute value, finally two values are relatively got in effectively clean that maximal value bears as production casing and are pressed.

Preferably, described salt cave closure causes in casing leak and salt cave top board leakage probability computation model, comprise that to the closed relevant event in salt cave casing leak and salt cave top board leak, suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the model shown in formula (7) and calculates the probability that salt cave closure causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}---\left(7\right)$

Wherein F (x) leaks for causing casing leak and salt cave top board the salt cave closing capacity distribution function occurring, and x is that note fells and transports the salt cave closing capacity (%) that row causes.

Preferably, in described step e, earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise:

E1 determines the relation of seismic amplitude and frequency according to Gutenberg – Richter rule;

E2 determines the relation of ground peak accelerator and seismic amplitude according to Gutenberg – Richter rule;

The relation of E3 based on described seismic amplitude and frequency and the relation of described ground peak accelerator and seismic amplitude, determine the seismic frequency of described salt cave well area and the relation of ground peak accelerator;

E4 determines that earthquake causes the described ground peak accelerator threshold value that well lost efficacy;

E5 is according to the relation of the seismic frequency of described salt cave well area and ground peak accelerator and described ground peak accelerator threshold value, determines distance between tomography and salt cave well and every year because earthquake causes the relation between frequency that salt cave well lost efficacy;

E6 every year because earthquake causes relation between frequency that salt cave well lost efficacy and the distance between salt to be evaluated cave well and tomography, determines that earthquake causes salt cave well failure probability according to described.

Preferably, the described different leakage mode in step F comprise little leakage, gross leak and the three kinds of patterns of breaking, wherein note adoptpipe diameter 1% for little leakage, it is gross leak that note is adopted 10% of pipe diameter, note adoptpipe diameter 100% for breaking.

Preferably, the described risk factors in step F cause that the elementary event probability of happening being associated is as follows:

Described risk factors are when corrosion, and it causes that elementary event is that the probability of happening of little leakage is

93%; When described risk factors are corrosion, it causes that elementary event is the generation of gross leak

Probability is 6.9%;

When described risk factors are corrosion, it causes that elementary event is that the probability of happening breaking is 0.1%;

When described risk factors are erosion, it causes that elementary event is that the probability of happening of little leakage is

93%; When described risk factors are erosion, it causes that elementary event is that the probability of happening of gross leak is 6.9%;

When described risk factors are erosion, it causes that elementary event is that the probability of happening breaking is 0.1%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening of little leakage is 70%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening of gross leak is 29%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening breaking is 1.0%;

Described risk factors are for operation is when relevant, and it causes that elementary event is that the probability of happening of little leakage is 39%;

Described risk factors are for operation is when relevant, and it causes that elementary event is that the probability of happening of gross leak is 60%;

When described risk factors are correlated with for operation, it causes that elementary event is that the probability of happening breaking is 1.0%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening of little leakage is 35%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening of gross leak is 64%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening breaking is 1.0%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening of little leakage is 26%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening of gross leak is 54%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening breaking is 20%.

Preferably, the part of taking charge described in step G refers to while jointly leaking for elementary event described in two or more, can control the elementary event of leakage size size in leak path.

Preferably, the probability of happening of the part of taking charge described in step H refers to, according to the probability of happening of the part of taking charge under the different leakage mode of formula (8) calculative determination, and is designated as the probability of happening of corresponding cut-set.

Pf_ij＝1-Π(1-Pf_jkA_ki)

（8）

Pf wherein_ijfor the leakage mode of the part j that the takes charge probability of happening that is i;

Pf_jkfor the probability of happening of part j under risk factors k impact of taking charge;

A_ikfor risk factors k causes the probability that leakage mode i occurs;

I is leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking;

J is main Case Number; K is risk factors, from 1-6 represent respectively that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force.

Preferably, the probability of happening of secondary event described in step I refers to by the probability of happening substitution formula (9) that causes the cut set of top event described in step H and calculates:

Pf_il＝1-Π(1-Pf_im)

（9）

Pf wherein_ilfor the leakage mode of the secondary event l probability of happening that is i;

Pf_imfor cut set is m and the leakage mode probability of happening while being i;

I is leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking; L is secondary Case Number; M is cut set numbering corresponding to secondary event.

Preferably, in step J, under different leakage mode, described top event probability of happening, according to fault tree in step C, comprises following two kinds of situations:

The first is that the logical relation between described secondary event is and door relation that the described top event of described different leakage mode is calculated by formula (10):

Pf_i＝ΠPf_il

（10）

The second is that the logical relation between described secondary event is or door relation, and the described top event of described different leakage mode is calculated by formula (11):

Pf_i＝1-Π(1-Pf_il)

（11）

Pf wherein_ifor salt cave well leaks into the probability of happening of the leakage mode i of atmosphere, i is leakage mode, and l is secondary Case Number.

The present invention has set up the fault tree that underground natural gas storage, salt cave storage medium leaks into ambient atmosphere environment, adopt the engineering judgment model of historical data statistical method and foundation, determined and caused that storage medium leaks into the elementary event probability of happening of ambient atmosphere environment, and with the form of correction factor, various risks factor is introduced in elementary event probability calculation the influence of elementary event probability of happening, simultaneously according to the principle of main event control leakage mode and fault tree logic, set up little leakage, the salt cave type underground natural gas storage storage medium of gross leak and fracture mode leaks into the method for calculating probability of ambient atmosphere environment, solved one of key issue of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave.The present invention can reasonably predict that salt cave type underground natural gas storage storage medium leaks into the probability of ambient atmosphere environment according to actual design parameter and operating mode situation, can be gas storage Secure Manager prevention underground natural gas storage, the salt cave leakage accident of adopting an effective measure foundation is provided.

Accompanying drawing explanation

Fig. 1 salt cave well storage medium leaks into the fault tree of ambient atmosphere environment.

The relation of Fig. 2 casing corrosion failure probability and working time.

The seismic salt of Fig. 3 cave well failure probability and salt cave well are to the distance of tomography.

Embodiment

Below in conjunction with embodiment, the present invention is further described in detail, the embodiment providing is only in order to illustrate the present invention, rather than in order to limit the scope of the invention.

Step 1: the information material that obtains underground natural gas storage, salt to be evaluated cave

Information material comprises underground natural gas storage, salt cave basic document, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor and maintenance/maintenance history data, as shown in table 2-table 6.

Underground natural gas storage, table 2 salt cave essential information

Numbering	Attribute	Unit	Parameter value
					1	Gas storage title	Text	Yan Xue underground natural gas storage, Jintan
2	Gas storage type	Text	Salt cave type
				2	Gas storage basic situation	Text	Current in-servicesalt cave Jing5Kou
3	Evaluate salt cave well numbering	Text	X1
				4	Salt cave well designed life	Year	50
5	Salt cave wellactive time	Year						4

Table 3X1 well storage medium characterisitic parameter

Numbering	Attribute	Unit	Parameter value
					1	Storage medium	Text	Rock gas
2	Gas constant	J/K.mol	8.314
				3	Rock gas molecular weight	kg/mol	0.023
4	Rock gas relative density	/	0.575
				5	The Dynamic Viscosity of rock gas	cp	0.000118

Table 4X1 well geometric shape parameters

Numbering	Attribute	Unit	Parameter value
					1	Salt cave volume	104m3	10.5
2	Storage capacity	104m3	1521
				3	Work tolerance	104m3	787
4	Cushion steam amount	104m3	734
				5	Salt cave mean diameter	m	40
6	Note is adopted sleeve pipe interior diameter	mm	159.4
				7	Production casing overall diameter	mm	244.5
8	Production casing wall thickness	mm	9.19
				9	Surface string overall diameter	mm	339.7
10	Surface string wall thickness	mm	9.65
				11	Note is adopted length of tube	m	940
12	Well head internal flow diameter	mm	159.4
				13	Well head wall thickness	mm	9.19
14	Flow diameter in emergency shut-in valve	mm	149.2
				15	Emergency shut-in valve wall thickness	mm	31.75

Table 5X1 operational factor

Numbering	Attribute	Unit	Parameter value
					1	Maximum well head operating pressure	kPa	13.5
2	Minimum well head operating pressure	kPa	6.5
				3	Averagewellhead pressure	kPa		10
4	Crude saltcave pressure	kPa							14
				5	Minimum saltcave pressure	kPa		7
6	Average salt cave pressure	kPa	10.5
				7	Salt cave temperature		53
8	Gasinput temp	C						20
				9	Peak performance (MPR)	104m3/d	153
10	Average preformance (%MPR)		100%
				11	Atmospheremedial temperature	C		20
12	Annual days running	day	180
				13	The time that maximum day throughput rate moved in 1year	day		14
14	Salt cave make rate in time under arms	%	0.38

Table 6X1 well servicing/maintenance history data

Numbering	Attribute	Unit	Parameter value
					1	The incident of leakage having occurred	Inferior	0
2	The salt cave unstability event having occurred	Inferior	0
				3	Maintenance history	Text	Nothing

Step 2: identification causes the risk factors that salt cave well storage medium leaks into ambient atmosphere environment

The risk factors that salt cave well leaks comprise that burn into erosion, equipment failure, operation are relevant, mechanical damage and earthquake six classes.

Step 3: set up the fault tree that salt cave well storage medium leaks into ambient atmosphere environment

The salt cave well of take leaks into atmosphere as top event (seeing accompanying drawing 2), considers leaked and by underground two kinds, the ground situation that leaks into, identified 11 elementary events (table 7), 9 cut sets (table 8) by well head facility

Table 7 causes the elementary event that leaks into the generation of atmosphere top event

Numbering	Elementary event	Numbering	Elementary event
				X1	Emergency shut-in valve leaks	X7	Salt cave top board leaks
X2	Above tubing hanger, well head leaks	X8	Cap rock leaks
				X3	Packer leaks	X9	Casing leak
X4	Tubing leak	X10	By production casing cement mantle, leak
				X5	Below tubing hanger, well head leaks	X11	By surface string cement mantle, leak
X6	Leak path to ground

Table 8 causes the cut set that top event occurs

Step 4: the relation of determining elementary event and various risks factor

In conjunction with industry experience, the affect relation (table 9) of the various risks factor described in determining step 2 on elementary event probability of happening.In table, to hooking, show that event may be caused by corresponding risk factors.

The affect relation of table 9 various risks factor on elementary event probability of happening

Step 5: based on historical statistical data and engineering judgment model, calculate various risks factor and cause the elementary event probability of happening being associated.

Adopt engineering judgment model to calculate various risks factor and cause that the elementary event probability of happening process being associated is as follows:

Erosion causes that the probability of happening of elementary event X1, X2, X4 and X5 calculates

Erosion is relevant to elementary event X1, X2, X4 and X5, and the erosion CALCULATION OF FAILURE PROBABILITY model (formula 1) in available summary of the invention calculates,

Erosion CALCULATION OF FAILURE PROBABILITY model as shown inEquation 1

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\&times;\mathrm{ratio}=2.572\&times;{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\&times;\mathrm{ratio}---\left(1\right)$

E wherein_kfor erosion rate (times/year), W is that sand flow velocity (Kg/day) V is that flow rate (m/s) D is pipe diameter (mm), S_kfor geometric shape parameters, Pf_erosionfor erosion cause equipment failure probability (times/year); T is equipment wall thickness (mm); Ratio is that gas storage accounts for year ratio with throughput rate operation in maximum day.

Parameter and result of calculation are in Table 10, and flow rate is to obtain according to corresponding medial temperature and average calculation of pressure.

Table 10 erosion causes the probability of happening of elementary event X1, X2, X4 and X5

Corrosion causes that casing failure probability of happening calculates

Casing corrosion CALCULATION OF FAILURE PROBABILITY model is to increase based on the theoretical definite corrosion default of stress-strength Interference the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, as the formula (2).

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}<0}}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{SMTS}\right)\mathrm{dP}---\left(2\right)$

This model adopts Monte Carlo method to calculate, and wherein, f (d, L, t, D, SMTS, P) is variable d, L, and t, D, SMTS, the joint probability density function of P, D is sleeve pipe external diameter, the thickness that d is etch pit; T is wall thickness; L is the effective length of wall thickness loss; P is effectively interior pressure, the tensile strength that SMTS is material, LSF_burstfor limit state function, it is that operating pressure explosion occurs while surpassing the burst pressure of prediction that corrosion default increases the ultimate limit state cause the explosion of residue tube wall, and limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF_burst＝P_burst-P_op

（3）

As LSF > 0; LSF=0 and LSF<0 represent respectively safety, the limit and failure state;

$P_{\mathrm{burst}}={\mathrm{\&sigma;}}_{\mathrm{flow}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]---\left(4\right)$

σ_flow＝SMTS

（5）

$M={[1+\frac{0.8L^2}{\mathrm{Dt}}]}^{1/2}---\left(6\right)$

P wherein_burstfor prediction failure stress, σ_flowfor flow stress, M is Folia coefficient; A is the area of metal loss

a₀for original area (L * t);

P_opin effectively clean, press, first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as overpressure, and subtract each other with pipe external pressure, take absolute value, during conservative, finally two values are relatively got to effectively clean interior pressure that maximal value is born as production casing.

Corrode relevantly to elementary event X3, X4 and X9, the probability of happening of X3, X4 adopts historical statistical data, and the casing corrosion CALCULATION OF FAILURE PROBABILITY model in the described step e in summary of the invention that adopts of elementary event X9 calculates.Adopt Monte Carlo method, consider that two kinds of corrosion rate 0.15mm/ and 0.24mm/ have calculated the Changing Pattern of casing corrosion failure probability with working time, see accompanying drawing 3, because this salt cave well active time is 4 years, the casing corrosion failure probability 2 * 10 while getting 4 years^-7times/year.

Salt cave closure causes that casing leak and salt cave top board leakage probability calculate

Salt cave closure causes casing leak and salt cave top board leakage probability computation model, comprise that to the closed relevant event in salt cave casing leak and salt cave top board leak, suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the model shown in formula (7) and calculates the probability that salt cave closure causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}---\left(7\right)$

Wherein F (x) leaks for causing casing leak and salt cave top board the salt cave closing capacity distribution function occurring, and x is that note fells and transports the salt cave closing capacity (%) that row causes.

By table 5 under arms the salt cave make rate 0.38% in the time be updated to the formula instep e 7 described in summary of the invention,

Obtain salt cave closure and cause that casing leak and salt cave top board leakage probability are 2.17 * 10-15 times/year.

Earthquake causes salt cave well CALCULATION OF FAILURE PROBABILITY

Earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise:

E1 determines the relation of seismic amplitude and frequency according to Gutenberg – Richter rule;

E2 determines the relation of ground peak accelerator (PGA) and seismic amplitude according to Gutenberg – Richter rule;

E3, based onstep 1 and the definite relation of step 2, determines the seismic frequency of certain salt cave well area and the relation of ground peak accelerator (PGA);

E4 determines that earthquake causes the PGA threshold value that well lost efficacy;

E5 is according to the PGA threshold value of the relation ofstep 3 andstep 4, determines distance between tomography and salt cave well and every year because earthquake causes the relation between frequency that salt cave well lost efficacy;

E5, according to the distance between the definite relation ofstep 5 and salt to be evaluated cave well and tomography, determines that earthquake causes salt cave well failure probability.

According to earthquake in the described step e in summary of the invention, cause the CALCULATION OF FAILURE PROBABILITY model of salt cave well, determined the relation of distance between salt cave well failure probability and salt cave well and tomography, see accompanying drawing 4.In embodiment, X1 well spacing is 500Km from the distance of tomography, and salt cave well failure probability is looked into the known 6 * 10-4 times/year of being of figure.For during conservative, suppose that seismic events only causes that elementary event X1 and X9 occur, remember elementary event X1 and X9 because of seismic probability of happening be 6 * 10-4 times/year.Various risks factor causes that the elementary event probability of happening being associated is in Table 11.

Table 11 various risks factor causes the elementary event probability of happening being associated

Step 6: determine that various risks factor causes that different leakage mode leak into the probability distribution rule that atmosphere occurs

Leak underground natural gas storage can be divided into little leakage, gross leak and the three kinds of patterns of breaking, and for underground natural gas storage leakage size, can define as follows: little leakage-note is adopted 1% of pipe diameter; Gross leak-note is adopted 10% of pipe diameter; Break-note to adopt and manage 100% of diameter.It is different that various risks factor causes that different leakage mode are leaked the probability occurring, and probability distribution can be calculated by the table 1 in technical scheme.

Various risks factor causes that different leakage mode leak into the probability distribution that atmosphere occurs and calculate by the table 1 in the described step F in summary of the invention, and wherein for natural force factor, 1 of the present embodiment is considered by earthquake.

Step 7: determine the part of taking charge that respectively cuts centralized control leakage mode

By the described step F in summary of the invention, determine the part of taking charge that respectively cuts centralized control leakage mode, the results are shown in Table 12.

Table 12 respectively cuts the part of taking charge of centralized control leakage mode

Step 8: the probability of happening of take charge part and the corresponding cut-set of different leakage mode calculates

Probability of happening with the little leakage of part X1-of taking charge is calculated as example, according to the G of step described in summary of the invention and table 12, calculates, and calculating the little leakage probability of happening of part X1-that shows to take charge is 9.7 * 10-3, and corresponding cut-set [X1]-little leakage probability of happening is 9.7 * 10-3.The probability of happening result of calculation of the different leakage mode of part of taking charge is in Table 13.

Pf_1X1＝1-(1-Pf_X12A₂₁)(1-Pf_X13A₃₁)(1-Pf_X15A₅₁)(1-Pf_X16A₆₁)

Pf_1X1＝1-(1-4.93×10^-8×0.93)(1-1.37×10^-2×0.7)(1-6.79×10^-6×0.35)(1-6×10^-4×0.26)＝9.7×10^-3

The take charge probability of happening of the different leakage mode of part of table 13

Step 9: the probability of happening that calculates the different leakage mode of secondary event under top event

2 fault trees can determine that the secondary event under top event is A1 and A2 with reference to the accompanying drawings, by the probability of happening substitution formula (9) of cut set corresponding to the secondary event in step I, calculate the probability of happening of the different leakage mode of secondary event.The little leakage mode probability of happening of secondary event A1 of take is example explanation computation process (formula).Table 14 is the probability of happening result of the different leakage mode of secondary event under top event.

Pf_1A1＝1-(1-Pf_1[x1])(1-Pf_1[x2])(1-Pf_1[x5])

Pf_1A1＝1-(1-9.7×10^-3)(1-2.8×10^-3)(1-2.97×10^-1)＝3×10^-1

The probability of happening of the different leakage mode of table 14 time level event

Step 10: the top event probability of happening that calculates different leakage mode

Secondary event A1 and A2 close and are or door relation, by the probability of happening substitution formula (1) 1 of the different leakage mode of secondary event under the top event of calculating in step I, can calculate the top event probability of happening of different leakage mode, in Table 15.

The probability of happening that leaks into atmosphere of the different leakage mode of table 15

A kind of salt provided by the invention cave type underground natural gas storage storage medium leaks into the method for calculating probability of ambient atmosphere environment, is primarily characterized in that 1) determined that salt cave type underground natural gas storage storage medium leaks into probability calculation information needed data and the design parameter of ambient atmosphere environment; 2) risk factors that salt cave well storage medium leaked into ambient atmosphere environment classify as that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force six classes; 3) set up and be applicable to the fault tree that salt cave well storage medium leaks into ambient atmosphere environment; 4) determined the relation of elementary event and various risks factor; 5) set up the engineering judgment model with the elementary event probability of happening of various risks factor analysis connection, comprised that erosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause probability calculation model that casing leak and salt cave top board leak and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model; 6) determined that various risks factor causes that different leakage mode (little leakage, gross leak and break) leak into the probability distribution that atmosphere occurs; 7) nethermost elementary event in leak path is defined as to the part of taking charge; 8) form with correction factor is incorporated in the probability of happening calculating of the part of taking charge under different leakage mode by various risks factor to the influence of elementary event probability of happening; 9) probability of happening of the part of taking charge under different leakage mode is designated as to the probability of happening of its corresponding cut-set; 10), based on above feature, finally form the method for calculating probability that underground natural gas storage, a kind of salt cave storage medium leaks into ambient atmosphere environment.

The invention solves one of key issue of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave, can reasonably predict that underground natural gas storage, salt cave leaks into the probability of atmosphere according to actual design parameter and operating mode situation, can be gas storage Secure Manager prevention underground natural gas storage, the salt cave leakage accident of adopting an effective measure foundation is provided.

Claims (21)

1. an assay method for risk of storage medium leakage of underground natural gas storage reservoir, is characterized in that, the method based on fuzzy fault tree is measured risk of storage medium leakage of underground natural gas storage reservoir, comprises the steps:

A obtains the data information of underground natural gas storage, salt to be evaluated cave;

The data information of B based on underground natural gas storage, described salt cave, identification causes the risk factors that storage medium leaks;

C is usingd and is leaked into atmosphere event as top event, determine secondary event, elementary event and cause the cut set of top event successively, sets up fault tree;

D determines the relation of described elementary event and described risk factors;

Data information and the engineering judgment model of E based on underground natural gas storage, described salt cave, calculates described risk factors and causes the elementary event probability of happening being associated;

F determines that described risk factors cause that different leakage mode leak into the probability distribution that atmosphere occurs;

Described in G basis, cause top event cut set, described in determining, cause in top event cut set and cause and leak into the part of taking charge that atmosphere event occurs;

H distributes according to described elementary event probability of happening and described risk factors leakage probability, the probability of happening of the part of taking charge described in determining and described in cause the probability of happening of the cut set of top event;

I according to described in take charge probability of happening and the described fault tree of part, calculate the probability of happening of described secondary event under described top event;

J, according to the probability of happening of described fault tree and described secondary event, calculates the probability of happening of described top event under different leakage mode;

Wherein, the model of engineering judgment described in step e comprises that erosion CALCULATION OF FAILURE PROBABILITY model, casing corrosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause casing leak and salt cave top board leakage probability computation model and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model, wherein, described erosion CALCULATION OF FAILURE PROBABILITY model is as the formula (1):

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\&times;\mathrm{ratio}=2.572\&times;{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\&times;\mathrm{ratio}---\left(1\right)$

E wherein_kfor erosion rate, unit is times/year; W is sand flow velocity, and unit is Kg/day; V is flow rate, and unit is m/s; D is pipe diameter, and unit is mm; S_kfor geometric shape parameters, Pf_erosionfor erosion causes the probability of equipment failure, unit, be times/year; T is equipment wall thickness, and unit is mm; Ratio is that gas storage accounts for year ratio with throughput rate operation in maximum day.

2. assay method according to claim 1, it is characterized in that, the data information of underground natural gas storage, salt to be evaluated cave described in steps A comprises salt cave underground gas storage library information, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor, maintenance and/or maintenance history data.

3. assay method according to claim 2, is characterized in that, underground natural gas storage, the cave of salt described in steps A information comprises gas storage title, gas storage type, evaluates salt cave well numbering, salt cave well designed life and salt cave well active time.

4. assay method according to claim 2, is characterized in that, the characterisitic parameter of storage medium described in steps A comprises the Dynamic Viscosity of storage medium type, gas constant, rock gas molecular weight, rock gas relative density and rock gas.

5. assay method according to claim 2, is characterized in that, the cave of salt described in steps A well geometric shape parameters comprises salt cave volume, storage capacity, work tolerance, cushion steam amount and tubing string size.

6. assay method according to claim 2, it is characterized in that, operational factor described in steps A comprises the maximum operating pressure of well head, the minimum operating pressure of well head, salt cave maximum design pressure, salt cave minimal design pressure, salt cave temperature, injecting gas temperature and peak performance.

7. assay method according to claim 2, is characterized in that, described in steps A, maintenance and/or maintenance history comprise the incident of leakage having occurred, the salt cave unstability event and the maintenance history that have occurred.

8. assay method according to claim 1, is characterized in that, risk factors described in step B classify as that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force six classes.

9. assay method according to claim 1, is characterized in that, leaks and be described secondary event by the underground ground that leaks in step C by well head facility.

10. assay method according to claim 9, is characterized in that, describedly by well head facility, is leaked and to be comprised that emergency shut-in valve leaks, above tubing hanger, below well head leakage, packer leakage, tubing leak and tubing hanger, well head leaks.

11. assay methods according to claim 9, it is characterized in that, described by undergroundly leaking into that ground comprises that packer leaks, leak path, the leakage of salt cave top board, cap rock leakage, casing leak to ground, by production casing cement mantle, leak and leak by surface string cement mantle.

12. assay methods according to claim 1, it is characterized in that, the cut set that causes top event described in step C comprises 6 cut sets, be followed successively by cut set 1 for emergency shut-in valve leakage, cut set 2 is that above tubing hanger, well head leaks, cut set 3 is packer leakage, below tubing leak and tubing hanger, well head leaks, cut set 4 is the leak path to ground, salt cave top board leaks and cap rock leaks, cut set 5 is packer leakage, casing leak, by production casing cement mantle, leak and leak by surface string cement mantle, cut set 6 is for to be leaked and to be leaked by surface string cement mantle by production casing cement mantle.

13. assay methods according to claim 1, is characterized in that, described casing corrosion CALCULATION OF FAILURE PROBABILITY model is to increase based on the theoretical definite corrosion default of stress-strength Interference the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, as the formula (2):

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}<0}}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{SMTS}\right)\mathrm{dP}---\left(2\right)$

This model adopts Monte Carlo method to calculate, wherein, and Pf_burstfor casing corrosion failure probability, unit is times/year, and f (d, L, t, D, SMTS, P) is variable d, L, and t, D, SMTS, the joint probability density function of P, D is sleeve pipe external diameter, unit is mm, the thickness that d is etch pit, unit is mm; T is wall thickness, and unit is mm; L is the effective length of wall thickness loss, and unit is mm; P is effectively interior pressure, and unit is kPa, the tensile strength that SMTS is material, and unit is kPa, LSF_burstfor limit state function, it is that explosion occurs while surpassing the burst pressure of prediction operating pressure that corrosion default increases the ultimate limit state cause the explosion of residue tube wall; Limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF_burst=P_burdt-P_op (3)

As LSF > 0; LSF=0 and LSF<0 represent respectively safety, the limit and failure state;

$P_{\mathrm{burst}}=\stackrel{\&OverBar;}{P_{\mathrm{burst}}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]---\left(4\right)$

（5）

$M={[1+\frac{0.8L^2}{\mathrm{Dt}}]}^{1/2}$

（6）

P wherein_burstfor prediction failure stress, unit is kPa;

for flow stress, unit is kPa; M is Folia coefficient; A is the area of metal loss,

a₀for original area, i.e. L * t, unit is mm^2,sMTS is the tensile strength of shell material, and unit is kPa; P_opin effectively clean, press, first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as overpressure, and subtract each other with pipe external pressure, take absolute value, finally two values are relatively got in effectively clean that maximal value bears as production casing and are pressed.

14. assay methods according to claim 1, it is characterized in that, described salt cave closure causes in casing leak and salt cave top board leakage probability computation model, comprise that to the closed relevant event in salt cave casing leak and salt cave top board leak, suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the model shown in formula (7) and calculates the probability that salt cave closure causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}---\left(7\right)$

Wherein F (x) leaks for causing casing leak and salt cave top board the salt cave closing capacity distribution function occurring, and x, for note fells and transports the salt cave closing capacity that row causes, represents with number percent.

15. assay methods according to claim 1, is characterized in that, in described step e, earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise:

E1 determines the relation of seismic amplitude and frequency according to Gutenberg – Richter rule;

E2 determines the relation of ground peak accelerator and seismic amplitude according to Gutenberg – Richter rule;

The relation of E3 based on described seismic amplitude and frequency and the relation of described ground peak accelerator and seismic amplitude, determine the seismic frequency of described salt cave well area and the relation of ground peak accelerator;

E4 determines that earthquake causes the described ground peak accelerator threshold value that well lost efficacy;

E5 is according to the relation of the seismic frequency of described salt cave well area and ground peak accelerator and described ground peak accelerator threshold value, determines distance between tomography and salt cave well and every year because earthquake causes the relation between frequency that salt cave well lost efficacy;

E6 every year because earthquake causes relation between frequency that salt cave well lost efficacy and the distance between salt to be evaluated cave well and tomography, determines that earthquake causes salt cave well failure probability according to described.

16. assay methods according to claim 1, it is characterized in that, the described different leakage mode in step F comprise little leakage, gross leak and the three kinds of patterns of breaking, and wherein noting and adopting 1% of pipe diameter is little leakage, note adopt pipe diameter 10% for gross leak, note adopt pipe diameter 100% for breaking.

17. assay methods according to claim 16, is characterized in that, the described risk factors in step F cause that the elementary event probability of happening being associated is as follows:

Described risk factors are when corrosion, and it causes that elementary event is that the probability of happening of little leakage is 93%;

Described risk factors are when corrosion, and it causes that elementary event is that the probability of happening of gross leak is 6.9%;

When described risk factors are corrosion, it causes that elementary event is that the probability of happening breaking is 0.1%;

When described risk factors are erosion, it causes that elementary event is that the probability of happening of little leakage is 93%;

When described risk factors are erosion, it causes that elementary event is that the probability of happening of gross leak is 6.9%;

When described risk factors are erosion, it causes that elementary event is that the probability of happening breaking is 0.1%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening of little leakage is 70%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening of gross leak is 29%;

When described risk factors are equipment failure, it causes that elementary event is that the probability of happening breaking is 1.0%;

Described risk factors are for operation is when relevant, and it causes that elementary event is that the probability of happening of little leakage is 39%;

Described risk factors are for operation is when relevant, and it causes that elementary event is that the probability of happening of gross leak is 60%;

When described risk factors are correlated with for operation, it causes that elementary event is that the probability of happening breaking is 1.0%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening of little leakage is 35%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening of gross leak is 64%;

When described risk factors are mechanical damage, it causes that elementary event is that the probability of happening breaking is 1.0%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening of little leakage is 26%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening of gross leak is 54%;

When described risk factors are natural force, it causes that elementary event is that the probability of happening breaking is 20%.

18. assay methods according to claim 1, is characterized in that, the part of taking charge described in step G refers to while jointly leaking for elementary event described in two or more, can control the elementary event of leakage size size in leak path.

19. assay methods according to claim 1, is characterized in that, the probability of happening of the part of taking charge described in step H refers to, according to the probability of happening of the part of taking charge under the different leakage mode of formula (8) calculative determination, and are designated as the probability of happening of corresponding cut-set:

Pf_ij=1-Π(1-Pf_jkA_ki)

（8）

Pf wherein_ijfor the leakage mode of the part j that the takes charge probability of happening that is i;

Pf_jkfor the probability of happening of part j under risk factors k impact of taking charge;

A_ikfor risk factors k causes the probability that leakage mode i occurs;

I is leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking;

J is main Case Number; K is risk factors, from 1-6 represent respectively that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force.

20. assay methods according to claim 1, is characterized in that, the probability of happening of secondary event described in step I refers to by the probability of happening substitution formula (9) that causes the cut set of top event described in step H and calculates:

Pf_il=1-Π(1-Pf_im)

（9）

Pf wherein_ilfor the leakage mode of the secondary event l probability of happening that is i;

Pf_imfor cut set is m and the leakage mode probability of happening while being i;

I is leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking; L is secondary Case Number; M is cut set numbering corresponding to secondary event.

21. assay methods according to claim 1, is characterized in that, in step J, under different leakage mode, described top event probability of happening, according to fault tree in step C, comprises following two kinds of situations:

The first is that the logical relation between described secondary event is and door relation that the described top event of described different leakage mode is calculated by formula (10):

Pf_i=ΠPf_il

（10）

The second is that the logical relation between described secondary event is or door relation, and the described top event of described different leakage mode is calculated by formula (11):

Pf_i=1-Π(l-Pf_il)

（11）

Pf wherein_ifor salt cave well leaks into the probability of happening of the leakage mode i of atmosphere, i is leakage mode, and l is secondary Case Number.

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