Background technology
Shallow layer gas is exactly shallow biogas, the gas that to be organism produce under the biological chemistry action of low temperature mezzanine level anaerobic bacteria, its main Geochemical Markers is that component CH4 content is higher and carbon isotope light, and δ 13C1 value is generally-75 ‰ ~-55 ‰.
The existence of shallow layer gas substantially increases the difficulty controlling earth pressure balance; the possibility producing geologic hazard in shield driving process increases widely; for ensureing the safety of engineering construction; protect normally carrying out of the security of the lives and property of numerous workmens and engineering, strengthen more seeming that it is significant to the research of shallow layer gas.
At present the method for exploration of shallow layer gas is mainly contained:
(1) static sounding
From the 1950's to the end of the eighties, Hangzhou Bay Region Biogas Exploration to have passed through on four the exploration history under four.Until the beginning of the nineties, static sounding technology is succeeded after application in shallow biogas exploration, just achieves certain exploration effects in some areas, defines certain rock gas productive capacity.Static sounding is a kind of home position testing method conventional in ground engineering prospecting, and it is the investigation way that exploration combines with test.Its principle is with static(al) by probe press-in stratum, the resistive force sensor in utilization probe.The penetration resistance (static point resistance qc and sidewall friction power fs) of being popped one's head in by electronic measuring instrument record.Because the size of penetration resistance is relevant with the character on stratum, the change therefore by analyzing penetration resistance can reach the object understanding formation properties.The advantage that static sounding Technology application is explored in shallow layer gas is: 1. equipment is light, with low cost, is only about 1/10 of same degree of depth rotary drilling cost; 2. can obtain qc and fs curve with brill, can be used for judging vertical succession of strata, not need to bore completion electrical measurement again; 3. whether gassiness can be qualitatively judged in drilled stratum.But its limitation is: 1. investigation depth is limited, generally more than 50 rice can only be detected in Hangzhou Bay Region; 2. be not suitable for gravel bed, meet containing gravel more than 30% time, data there will be distortion and even cannot creep into; 3. due to the too little easy blocking of well, be generally not suitable for beating producing well.
(2) seismic prospecting
One-tenth according to rock gas hides principle, and the rock gas that namely density is little is discharged from angry layer, controls upwards to migrate along the hole in stratum by buoyancy.Upper cover the sealing role of confining bed under can not upwards migrate further or loss, can only lateral migration in layer dredged, converge at the top of layer of sand or lens sand body.In the convergence process of shallow gas, the space occupied by former pore water in layer of sand is constantly squeezed in the convergence of gas, pools gas reservoir gradually at the top of sand body, and the hole of bottom layer of sand is still moisture, and formation gas, water are with the gas reservoir of layer.Due to gassiness in the layer of sand hole that underlies, its block density is little, and the difference of impedance above covered between clay is relatively large, and its reflecting interface reflection amplitude on seismic section is relatively strong, and this identifies the favourable foundation of METHOD OF SHALLOW GAS RESERVOIRS.
(3) non-seismic geophysical and geochemical exploration method
Non-seismic geophysical and geochemical exploration method mainly comprises geological radar, gravity negative effect, echo depth sounding and sonar, induced polarization, hydrocarbon geochemical exploration, remote sensing, electrostatic Alpha (α) measured thin film, microbial method etc., and wherein electrostatic a film measuring and microbial process effect in sparker survey is better.
1. electrostatic a film measuring
Normal and the oil gas symbiosis of uranium in sedimentogeneous rock.Hydrocarbon zone is in strong reducing environment, the radium be dissolved in the water and part uranium by the vertical movement of water component to globak migration.The decay product radon of uranium and radium also by convection current, diffusion or along crack, shatter belt upwards moves, and therefore, above hydrocarbon-bearing pool, often occurs Radon Anomaly.Whether the radon consistence size recorded according to earth's surface can descend the existence of hydrocarbon-bearing pool speculatively.Practice shows, presents faint low value radioactivity anomaly above numerous oil gas fields, substantially corresponds to oil gas field profile in the plane, and often occurs radioactivity high-value sector at oil gas field edge.
Electrostatic a film measuring is first by the poly-vinegar film card of band-1000V voltage, be embedded in 40cm place, underground, take out card through certain hour, measure the transmitted intensity on card with the radiation gauge of Alpha (α), judge gas reservoir by the Radon Anomaly quantitative value measured.
Found by the test in Hangzhou Bay Region, electrostatic Alpha (α) measured thin film method is a kind of new method that is effective, prospecting shallow layer gas fast, it is characterized in that the border of hiding according to the Radon Anomaly delineation shallow biogas occurred directly over gas field.Radon survey method has the advantages such as disturbing factor is few, highly sensitive, favorable reproducibility, on-the-spot quick obtaining result, economical and effective.
2. microbial method
In Xiaoshan, Zhejiang area, successively acquire more than 200 pedotheque carries out microbiological prospecting research to 1998-1999, experimentally analyze, determine that methanobacteria is the indicator bacteria of shallow biogas, other 5 kinds of soil bacterias (Flavobacterium, bacillus, Acinetobacter, Xanthomonas and Pseudomonas) content and distribution situation also have certain indicative function.
3. resistivity prospecting
EH4 electric magnetic image combines controlled-source audiomagnetotellurics method (CSAMT) and magnetotelluric method (MT), becomes a kind of tensor formula conductivity measurement system of novel concept.This system uses Natural electromagnetic field and artificial electromagnetic field signal, can measure the change of resistivity in several meters to the 1000m degree of depth, and the serial section of conductivity variations under various topographic condition can be obtained.This system has lightly portable, easy to operate, the advantage such as simple, with low cost of constructing, and is very applicable to shallow-layer geologic prospecting.EH4 electric magnetic image predictably descends geological condition by the change of measured resistivity, and that is, when the resistivity contrasts that underground is adjacent to plastid reaches certain value, they just can be distinguished by electric magnetic image.For the gassiness layer of sand of Hangzhou Bay Region, the gassiness layer of sand of Hangzhou Bay Region is sandwiched in valley flat-estuary deposit, buried depth is more shallow, but because incised valley is subject to the impact of tidal action, in layer of sand, the salinity of local water is relatively high, total mineralization, generally at about 10000mg/1, has satisfactory electrical conductivity; Gas-bearing formation poorly conductive, resistivity are higher, form significant difference with the resistivity of water layer.Thus, can by measure gas-bearing formation and normally layer resistivity difference identify gas-bearing formation.
Summary of the invention
The invention provides a kind of shallow layer gas detection method, solve probe free dropping, probe blocks, flowmeter range is discontented with a series of difficult problems such as sufficient traffic requirement.
Shallow layer gas detection method of the present invention, comprises the following steps:
A. prospecting in early stage: in prospecting process, be connected with feeler lever by probe, load static penetrometer, pressing down in process to pop one's head at feeler inspection and to be connected all the time with feeler lever, when arriving assigned address, above carrying feeler lever, probe can be separated automatically with feeler lever, now give vent to anger outward by feeler lever center-aisle if any gas, as air pressure and flow very I first use BXC-02 Application of Combustible Gas Indicator, measure at feeler lever mouth and whether have gas to overflow;
B. on-the-spot test: in order to accurately record the base plate buried depth of gas-bearing horizon, first with static pressure equipment, feeler lever is pressed into below ground predetermined depth place, then slowly feeler lever is upwards mentioned, look into and see if there is gas overflowing, if when finding that there is gas overflowing in the process mentioned, then the degree of depth at this place is gas-bearing horizon base plate buried depth; Feeler lever end head is blocked in order to prevent earth, can adopt gas cylinder in feeler lever, be pressed into the gas of 1MPa pressure, close after 3 minutes, adopt BXC-02 Application of Combustible Gas Indicator, detect in gas outlet and whether have inflammable gas, the degree of depth if any inflammable gas then this place is gas-bearing horizon base plate buried depth, as without find feeler lever often on carry 0.5m-1m can duplicate detection once, until through the gas-bearing horizon intending existence, the determination of top board buried depth can be considered determine according to the concrete geology Information integration of the overlayer of gas-bearing horizon and gas-bearing horizon.
Compared with prior art, beneficial effect of the present invention is: 1, equipment and instrument ample supply of commodities on the market; 2, processing step is rigorous, and continuity requires high; 3, the key parameter design of technique is strict, has generalization to soft clay area; 4, processing step is simple to operate easy to learn; 5, actual verification illustrates that the data measured accurately and reliably; 6, city underground engineering investigation and prospecting can be widely used in.
Embodiment
Below in conjunction with Fig. 1, the specific embodiment of the present invention is described in further detail.
The shallow layer gas detection method of the present embodiment carries out according to following steps,
A. prospecting in early stage: in prospecting process, first be connected with feeler lever by homemade probe and load static penetrometer, press down in process to pop one's head at feeler inspection and to be connected all the time with feeler lever, when arriving assigned address, on carry feeler lever, popping one's head in can be separated automatically with feeler lever, now gives vent to anger outward by feeler lever center-aisle if any gas, as air pressure and flow very I first use BXC-02 Application of Combustible Gas Indicator, measure at feeler lever mouth and whether have gas to overflow.
BXC-02 Application of Combustible Gas Indicator principle of work and the scope of application: BXC-02 Application of Combustible Gas Indicator sensor, with the tested gas reaction of diffusion way directly and in environment, produces the voltage signal of linear change.Signal processing circuit is made up of the polylith integrated circuit based on intelligent chip.Sensor output signal is through filter and amplification, and analog to digital conversion, the process such as model calculation, directly at the concentration value of the tested gas of liquid crystal screen display.When gas concentration reaches preset alarming value, instrument, by the difference according to alert levels, sends the sound of different frequencies, visual alarm.BXC-02 Application of Combustible Gas Indicator, is applicable to the concentration of the inflammable gas such as continuous detecting alkanes, alcohols and organic volatile in working environment, can be widely used in the security protection of the industries such as oil, chemical industry, rock gas, fire-fighting.
B. on-the-spot test: in order to accurately record the base plate buried depth of gas-bearing horizon, first with static pressure equipment, feeler lever is pressed into below ground predetermined depth place, then slowly feeler lever is upwards mentioned, look into and see if there is gas overflowing, if when finding that there is gas overflowing in the process mentioned, then the degree of depth at this place is gas-bearing horizon base plate buried depth; Feeler lever end head is blocked in order to prevent earth, can adopt gas cylinder in feeler lever, be pressed into the gas of 1MPa pressure, close after three minutes, adopt BXC-02 Application of Combustible Gas Indicator, detect in gas outlet and whether have inflammable gas, the degree of depth if any inflammable gas then this place is gas-bearing horizon base plate buried depth, as without find feeler lever often on carry 0.5m-1m can duplicate detection once, until through the gas-bearing horizon intending existence, the determination of top board buried depth can be considered determine according to the concrete geology Information integration of the overlayer of gas-bearing horizon and gas-bearing horizon.
The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the prerequisite not departing from the technology of the present invention principle; can also make some improvement and modification, these improve and modification also should be considered as protection scope of the present invention.