Disclosure of Invention
The invention provides a method for determining the effective thickness of a buried hill reservoir through a well test curve, which is used for accurately obtaining the actual effective thickness of a large section of buried hill reservoir within the detection radius of a test well.
The invention relates to a method for determining the effective thickness of a reservoir of a down-the-mine through a well test curve, which comprises the following steps:
A. acquiring output and bottom hole pressure data of a test well in different working systems;
B. C, calculating a bottom hole pressure derivative when closing the well according to the bottom hole pressure data obtained in the step A, and obtaining a bottom hole pressure derivative curve;
C. determining the thickness hW of a contributing layer section of a reservoir around a shaft through a production logging technology;
D. b, establishing a buried hill reservoir dual medium spherical flow interpretation model according to the yield obtained in the step A;
E. And D, bringing the thickness hW of the reservoir contribution layer section around the shaft in the step C into the spherical flow interpretation model of the dual medium of the subsurface reservoir in the step D, generating a bottom-hole pressure derivative graph curve, performing optimization fitting on the bottom-hole pressure derivative graph curve and the bottom-hole pressure derivative graph in the step B, and calculating to obtain optimized reservoir parameters and reservoir effective thickness.
According to the well test method, the distribution range of a reservoir fluid system is determined through the underground fluid pressure change and recovery process, and information such as reservoir permeability and productivity is determined. In general, data is obtained by logging techniques, which are used to guide the next well test. Logging refers to measuring physical parameters of formations around a borehole, such as acoustic waves, resistivity, neutron density, natural gamma ray intensity and the like, by various downhole instruments, and realizing lithology recognition, reservoir partitioning, determination of hydrocarbon and water layers and evaluation of reservoir parameters by logging technical interpretation.
The invention judges whether the large section of the down-the-hole test well has spherical flow characteristics by using a well test curve method, interprets the production layer contribution section around the shaft by combining the production logging technology, and obtains the actual effective thickness of the whole reservoir by the optimized fitting analysis of the well test curve (namely, the bottom pressure derivative curve) and the model curve (namely, the bottom pressure derivative plate curve).
In the prior art, the technologies of earthquake, logging, core analysis and the like all belong to static evaluation methods, and the technology reflects stratum properties of a borehole or the vicinity thereof. The invention is based on the well test dynamic test, can well represent the actual characteristics of the reservoir under the dynamic condition, reflects the effective thickness of the reservoir in the larger detection range of the test well and the periphery thereof, and provides guidance for the exploration of the reservoir declaration and the formulation of the overall development scheme.
Further, the test well in the step A is an oil well or a gas well, and the yield comprises one or more of liquid yield, oil yield, water yield and gas yield.
Furthermore, the working system in the step A refers to two working states of a test well realized according to the sequence of firstly opening the well for production and then closing the well; the open-well production is a process of realizing one or more production changes by changing the size of a choke.
A specific calculation method is that the calculating of the bottom hole pressure derivative in the well closing process in the step B comprises the following steps: and D, calculating to obtain a bottom hole pressure derivative changing with time according to the bottom hole pressure data obtained in the step A:
Wherein pwD' is the bottom hole pressure derivative,For the bottom hole pressure derivative at time node tk, dpwD is the bottom hole pressure derivative, pwD is the bottom hole pressure, d is the increment of pwD, t is the shut-in time, L is half the smooth window length, k+L is the window rightmost data point position, and k-L is the window leftmost data point position.
Further, in the step C, the thickness hW of the reservoir contribution layer around the wellbore is determined by using a production logging technique, which is an interval of the test well in the step a participating in fluid flow in the open-hole production state is tested and explained by using the production logging technique, so as to obtain the thickness hW of the reservoir contribution layer around the wellbore.
Specifically, the production logging technology test is that parameter variables related to the depth of the open hole interval of the submarine mountain are tested and obtained through an instrument, and the method comprises the following steps: magnetic positioning, natural gamma ray intensity, water holdup, turbine speed, density, temperature and pressure; the magnetic positioning and natural gamma ray intensity are used for assisting the depth correction of other parameter variables, the density and the water holding rate are used for identifying the fluid holding rate of each phase in the mixed phase fluid, the temperature and the pressure are used for setting high-pressure physical parameters of the fluid, and the turbine rotating speed is used for calculating the apparent flow rate of the fluid in the well.
Interpreted by production logging means, the production profile of a large section of subsurface reservoirs and the reservoir contribution interval thickness hW around the wellbore are obtained by production logging means.
Further, in the step D, when the buried-hill reservoir dual-medium spherical flow interpretation model is established, according to the obtained production of the test well, the dependent variables and the independent variables of the buried-hill reservoir dual-medium spherical flow interpretation model are obtained, wherein the dependent variables comprise bottom hole pressure pwD, the independent variables comprise production, reservoir parameters and time t, and the production is the production of the last open well before well closing.
And D, determining the buried hill reservoir dual-medium spherical flow interpretation model in the step D according to the type of the oil and gas reservoir, the inner boundary condition and the outer boundary condition. For the situation that micro cracks exist in a submarine mountain reservoir for comparison development, a characteristic curve of the submarine mountain reservoir dual-medium spherical flow interpretation model shows the characteristics of a dual-medium model; for the open hole production of the large section of the submarine mountain, and the situation that part of the layer sections do not participate in the flow exists, the characteristic curve of the submarine mountain reservoir dual-medium spherical flow interpretation model shows the characteristic of spherical flow.
Further, in the optimization fitting process, the thickness hW of the reservoir contribution layer section around the shaft in the step C, the initial value of the reservoir parameter and the initial value of the reservoir effective thickness are brought into the spherical flow interpretation model of the dual medium of the subsurface reservoir in the step D, corresponding bottom hole pressure derivative graph curves are generated by adjusting different values of the reservoir parameter and the reservoir effective thickness, and the bottom hole pressure derivative graph curves and the bottom hole pressure derivative curve in the step B are subjected to the optimization fitting calculation to obtain the optimized reservoir parameter and the optimized reservoir effective thickness. And the initial values of the reservoir parameters and the initial values of the effective thickness of the reservoir are obtained by the interpretation result of the logging technology.
Specifically, the optimization fitting is achieved through a nonlinear regression algorithm.
The beneficial effects of the invention include:
1. Whether the test well has spherical flow characteristics or not can be judged through the well test curve characteristics of the measured data, and whether the large-section submarine test has the condition that the reservoir sections around the well shaft do not participate in the flow or not is determined.
2. And generating an interpretation chart (a bottom hole pressure derivative chart curve) through a buried hill reservoir dual medium spherical flow interpretation model, and obtaining the quantitative relation between the thickness of a reservoir contribution section around the shaft and the effective thickness of the reservoir through optimal fitting with measured data.
3. And the thickness of the reservoir contribution interval around the shaft is interpreted by combining the production logging technology, so that quantitative interpretation of the effective thickness of the reservoir in the effective radial test range of the test well is realized.
4. Based on the well test dynamic test, the actual characteristics of the reservoir under the dynamic condition can be well represented, the effective thickness of the reservoir in the larger detection range of the test well and the periphery of the test well is reflected, and guidance is provided for the establishment of the exploration of the reserve declaration and the overall development scheme.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application, and it is apparent that the described embodiments are only some embodiments of the present application, not all embodiments. The components of the embodiments of the present application generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following detailed description of the embodiments of the application, as presented in the figures, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by a person skilled in the art without making any inventive effort, are intended to be within the scope of the present application.
As shown in fig. 1, the method for determining the effective thickness of the down-the-hill reservoir by using the well test curve comprises the following steps:
A. acquiring output and bottom hole pressure data of a test well in different working systems;
B. C, calculating a bottom hole pressure derivative when closing the well according to the bottom hole pressure data obtained in the step A, and obtaining a bottom hole pressure derivative curve;
C. determining the thickness hW of a contributing layer section of a reservoir around a shaft through a production logging technology;
D. b, establishing a buried hill reservoir dual medium spherical flow interpretation model according to the yield obtained in the step A;
E. And D, bringing the thickness hW of the reservoir contribution layer section around the shaft in the step C into the spherical flow interpretation model of the dual medium of the subsurface reservoir in the step D, generating a bottom-hole pressure derivative graph curve, performing optimization fitting on the bottom-hole pressure derivative graph curve and the bottom-hole pressure derivative graph in the step B, and calculating to obtain optimized reservoir parameters and reservoir effective thickness.
The invention judges whether the large section of the down-the-hole test well has spherical flow characteristics by using a well test curve method, interprets the production layer contribution section around the shaft by combining the production logging technology, and obtains the actual effective thickness of the whole reservoir by the optimized fitting analysis of the well test curve (namely, the bottom pressure derivative curve) and the model curve (namely, the bottom pressure derivative plate curve).
In the prior art, the technologies of earthquake, logging, core analysis and the like all belong to static evaluation methods, and the technology reflects stratum properties of a borehole or the vicinity thereof. The invention is based on the well test dynamic test, can well represent the actual characteristics of the reservoir under the dynamic condition, reflects the effective thickness of the reservoir in the larger detection range of the test well and the periphery thereof, and provides guidance for the exploration of the reservoir declaration and the formulation of the overall development scheme.
In step a, the test well is an oil or gas well, and the production includes one or more of liquid production, oil production, water production, and gas production. The working system refers to two working states of a test well realized according to the sequence of firstly opening the well for production and then closing the well; the open-well production is a process of realizing one or more production changes by changing the size of a choke. Various data acquisition methods for testing wells may be implemented with reference to the "oil field well test specification SY/T6172-2022" and the "gas well test specification SY/T5440-2019".
And B, calculating the bottom hole pressure derivative during well closing, wherein the bottom hole pressure derivative which changes along with time is calculated according to the bottom hole pressure data acquired in the step A:
Wherein pwD' is the bottom hole pressure derivative,For the bottom hole pressure derivative at time node tk, dpwD is the bottom hole pressure derivative, pwD is the bottom hole pressure, d is the increment of pwD, t is the shut-in time, L is the smooth window length, k+L is the window right-most data point position, and k-L is the window left-most data point position.
And C, determining the thickness hW of the reservoir contribution layer section around the shaft through the production logging technology, wherein the thickness hW of the reservoir contribution layer section around the shaft is obtained through the production logging technology testing and explaining the layer section of the test well participating in fluid flow in the open-hole production state in the step A.
The production logging technology test is that seven parameter variables related to the depth of a subsurface open hole interval are tested and obtained through an instrument, and the production logging technology test comprises the following steps: magnetic positioning, natural gamma ray intensity, water holdup, turbine speed, density, temperature and pressure; the magnetic positioning and natural gamma ray intensity are used for assisting the depth correction of other parameter variables, the density and the water holding rate are used for identifying the fluid holding rate of each phase in the mixed phase fluid, the temperature and the pressure are used for setting high-pressure physical parameters of the fluid, and the turbine rotating speed is used for calculating the apparent flow rate of the fluid in the well.
Interpreted by production logging means, the production profile of a large section of subsurface reservoirs and the reservoir contribution interval thickness hW around the wellbore are obtained by production logging means. For example, relevant parameters obtained by production logging technology test are input into corresponding interpretation software to be interpreted, so that the production profile of a large-scale subsurface reservoir and the thickness hW of reservoir contribution intervals around a shaft are obtained.
The method for testing and explaining the production profile of the large-section submarine mountain reservoir can refer to the 1 st part of injection, production profile logging data processing and explaining standard: "vertical well SY/T5783.1-2012" and section 2: "inclined shaft SY/T5783.2-2016" implementation.
And D, determining the spherical flow interpretation model of the dual medium of the subsurface reservoir in the step D according to the oil and gas reservoir type, the inner boundary condition and the outer boundary condition when the spherical flow interpretation model of the dual medium of the subsurface reservoir is established.
The reservoir type comprises one of a homogeneous oil or gas reservoir, a dual medium oil or gas reservoir, a double-seepage oil or gas reservoir and a compound oil or gas reservoir, and belongs to the dual medium oil or gas reservoir for the reservoir type of the subsurface mountain reservoir.
The internal boundary condition comprises one of a vertical well, an inclined well, a horizontal well, a partial jet, a limited diversion fracture and an infinite diversion fracture.
The outer boundary condition includes one of an infinite boundary, a circular closed boundary, a circular constant pressure boundary, one or two or three impermeable boundaries, one or two or three constant pressure boundaries.
And obtaining a dependent variable and an independent variable of a buried hill reservoir dual medium spherical flow interpretation model according to the obtained test well yield, wherein the dependent variable comprises bottom hole pressure pwD, the independent variable comprises yield, reservoir parameters and time t, and the yield is the yield of the last open-hole production before well closing.
For the situation that micro cracks exist in a submarine mountain reservoir for comparison development, a characteristic curve of the submarine mountain reservoir dual-medium spherical flow interpretation model shows the characteristics of a dual-medium model; for the open hole production of the large section of the submarine mountain, and the situation that part of the layer sections do not participate in the flow exists, the characteristic curve of the submarine mountain reservoir dual-medium spherical flow interpretation model shows the characteristic of spherical flow. FIG. 2 shows a schematic diagram of a dual medium spherical flow interpretation model of a subsurface reservoir, where H is the effective reservoir thickness, HW is the thickness of the reservoir contribution interval around the wellbore, H is the thickness of the entire subsurface reservoir test section, Za is the height from the top surface of the reservoir contribution interval around the wellbore to the top surface of the reservoir effective thickness interval, Zb is the height from the bottom surface of the reservoir contribution interval around the wellbore to the top surface of the reservoir effective thickness interval, arrows 1,2,3 are schematic diagrams of the flow lines of oil (or gas) in the reservoir, and arrow 1 represents the radial flow characteristics of the reservoir contribution interval around the wellbore; arrow 2 represents a spherical flow feature; arrow 3 represents the radial flow characteristics of the reservoir effective thickness section. FIG. 3 is a graph of characteristics of a well test curve (i.e., bottom hole pressure derivative graph curve) of a down-the-hole reservoir dual medium spherical flow interpretation model, wherein the graph is shown as a pressure characteristic curve at the upper part and a pressure derivative characteristic curve at the lower part in FIG. 3.
The buried hill reservoir dual medium spherical flow interpretation model is solved in Laplace space for bottom hole pressure pwD, and the process is as follows:
Wherein:
LD＝hw/h (5)；
Wherein: representing a solution of bottom hole pressure in Laplace space; The solution of bottom hole pressure in Laplace space when the skin coefficient and dimensionless well storage coefficient are not considered; u is a laplace variable; s is the skin coefficient; cD is a dimensionless well Chu Jishu; hD is the dimensionless reservoir thickness; zD is the dimensionless longitudinal distance; zaD and zbD are the dimensionless distance of the top and bottom surfaces of the reservoir contribution layer segments around the wellbore from the top surface of the reservoir effective thickness segment, respectively; k0(x)、K1 (x) is a Bessel function of the zero-order and first-order imaginary volume respectively; lambdam is a cross flow coefficient of a quasi-steady cross flow generated from a matrix to a crack; omegam is the elastic reservoir ratio of the matrix; omegaf is the elastic reservoir ratio of the fracture system; lD is the proportion of the thickness of the contribution layer section of the reservoir around the shaft to the effective thickness of the reservoir; hw is the wellbore surrounding reservoir contribution interval thickness; h is the effective thickness of the reservoir.
Obtained by Stehfest numerical inversionThe solution pwD of the bottom hole pressure in real space, deriving the bottom hole pressure can result in the pressure derivative pwD' of the bottom hole pressure.
The method for establishing and solving the buried hill reservoir dual-medium spherical flow interpretation model refers to 'modern well test interpretation method' (oil industry press) by Liao Xinwei and 'dual-medium partial jet seepage model and well test template curve' by Chen Fangfang (Daqing petroleum geology and development).
And E, when optimization fitting is carried out, obtaining an initial value of a reservoir parameter and an initial value of an effective reservoir thickness by a result interpreted by a logging technology, then bringing the initial value of the reservoir contribution layer section thickness hW around the shaft in the step C and the initial value of the reservoir parameter and the initial value of the effective reservoir thickness into the spherical flow interpretation model of the dual medium of the subsurface reservoir in the step D, generating a corresponding bottom hole pressure derivative plate curve by adjusting different values of the reservoir parameter and the effective reservoir thickness, and carrying out optimization fitting calculation on the bottom hole pressure derivative plate curve and the bottom hole pressure derivative curve in the step B to obtain the optimized reservoir parameter and the optimized reservoir effective thickness.
The optimization fit is achieved by a nonlinear regression algorithm, wherein the objective function is defined as follows:
Wherein: phi (x) is an objective function to be optimized; pwD1′(tk) is the pressure derivative corresponding to time tk, i.e. the one obtained by equation (1) of step BPwD2′(x,h,tk) is the pressure derivative obtained by passing through the formula (2) of the step D and performing Stehfest numerical inversion on the buried hill reservoir dual-medium spherical flow interpretation model at the moment tk, wherein x represents reservoir parameters and h represents reservoir effective thickness; n is the number of test pressure data points; σk is the standard deviation of the kth point measurement.
The variables to be optimized in the objective function are a reservoir parameter x and a reservoir effective thickness h.
The optimization fitting process is described with reference to John P.Spivey, method of interpretation of practical well tests (oil industry Press)
The effective thickness H of the reservoir obtained after the optimization fitting is smaller than the thickness H of the whole buried hill reservoir test section.
The invention is further described in connection with the following test data for a well:
the method for determining the effective thickness of the reservoir of the down-the-mine through the well test curve comprises the following steps:
A. The method is characterized in that an oil well of the subsurface reservoir is tested in an open hole well completion mode, the test well section is 2113 m-2608 m, and the overall thickness of the test section is 495m. In the production stage of well opening, 3 working systems are tested by adjusting a choke, and the ground metering yield is 167 square/day, 159 square/day and 330 square/day respectively; and closing the well after the last working system test is finished, and performing a pressure recovery test. A storage manometer on the test string obtains bottom hole pressure variation data during the test. The production and bottom hole pressure changes over time are shown in figure 4.
B. And calculating the derivative of the bottom hole pressure data in the well closing stage according to the corresponding relation between the measured output data and time. In the pressure derivative well test curve shown in FIG. 5, the duration of the shut-in phase is 12hr, and the spherical flow characteristics with a very pronounced-1/2 slope appear at the 0.01 hr-0.1 hr position on the log well test curve.
C. During open-hole testing, after running a tool of production logging technology, the contributing intervals of the reservoir around the full interval wellbore are measured, as shown in fig. 6. Production logging interpretation showed that the thickness of the major contributing interval was 96.6m, with a relative production rate of 100%
D. Establishing a buried hill reservoir dual-medium spherical flow interpretation model (hereinafter referred to as a model for short), wherein the radius of a shaft in the model is 0.108m, the porosity is 6.47%, the volume coefficient is 1.62, the viscosity of fluid under stratum conditions is 0.175cp, and the compression coefficient of oil is 0.0028MPa-1; the thickness of the section of the well (reservoir contributing section around the wellbore) partially participating in the flow in the model was 96.6m as explained in step C. Depending on the reservoir parameters and the effective reservoir thickness, a plurality of template curves of pressure derivatives (model pressure derivatives in fig. 3), i.e., a plurality of well test curves as shown in fig. 3, may be generated.
E. And (3) carrying out optimization fitting analysis on the template curve (i.e. fig. 3) of the pressure derivative (model pressure derivative in fig. 3) and the data of the measured pressure derivative (i.e. fig. 5) in the step (B) based on the objective function in the formula (6), so as to obtain the optimal reservoir parameter and the reservoir effective thickness value. The best fit analysis curve is shown in fig. 7. The overall relation is that the curve of the first figure 3 is generated according to the initial value of the reservoir parameter and the initial value of the effective thickness of the reservoir; by continuously adjusting the reservoir parameter x and the reservoir effective thickness h, generating a plurality of curves of figure 3, and fitting the figures 3 and 5 until the figure 7 state with the best fitting degree is reached, the obtained parameter is the optimal reservoir effective thickness h required by the invention. In fig. 7, the model pressure curve is overlapped with the test pressure curve at the upper part, and the model pressure derivative curve is overlapped with the test pressure derivative curve at the lower part. Reservoir parameters include detection radius, permeability, skin coefficient, well storage coefficient, energy storage ratio, and fluid channeling coefficient, etc. The detection radius of the well test is 210m and the thickness h is 162m through optimization fit analysis. Namely, the average effective thickness of the reservoir layer is 162m in the radius range of 210m by taking the well as the center of a circle. The effective thickness of the reservoir in the detection range is obtained through well test curve interpretation, and guidance is provided for reservoir reserve calculation and development scheme formulation.
The above examples merely illustrate specific embodiments of the application, which are described in more detail and are not to be construed as limiting the scope of the application. It should be noted that, for those skilled in the art, it is possible to make related modifications and improvements without departing from the technical idea of the application, which fall within the protection scope of the application.