CN114458308A - Method for evaluating original geological reserves of natural gas of fractured gas reservoir - Google Patents
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Abstract
The invention discloses an assessment method of original geological reserves of natural gas of a fractured gas reservoir, which comprises the steps of obtaining a water volume change rate and a rock pore volume change rate; calculating equivalent apparent pressure according to basic parameters of a gas reservoir, production dynamic data, a water volume change rate and a rock pore volume change rate; the method takes the changes of water volume and rock pore volume in the mining process into consideration, takes the changes of compression coefficient of the rock pore volume into consideration when calculating the changes of the rock pore volume, and converts the pressure of the whole gas reservoir into the equivalent visual pressure, thereby achieving the purpose of more accurate calculation result when calculating the original geological reserve of the special gas reservoir with crack property.
Description
Technical Field
The invention belongs to the technical field of natural gas exploitation, and particularly relates to an evaluation method for original geological reserves of natural gas of a fractured gas reservoir.
Background
The original geological reserves of natural gas of the gas reservoir are the primary key parameters for developing the gas reservoir, and can directly influence the reserve division of the gas reservoir, the calculation of development benefits and the determination of the development sequence. Before or in the initial development of the gas reservoir, the natural gas original geological reserve of the gas reservoir is generally estimated through a volumetric method, and in the development process of the gas reservoir, the natural gas original geological reserve of the gas reservoir is generally determined through a material balance method, namely, the gas reservoir is regarded as a container with a constant volume, and then the natural gas original geological reserve of the gas reservoir is calculated through basic parameters of the reservoir and production dynamic data. At present, the types of gas reservoirs are various, particularly for special gas reservoirs with abnormal high pressure and crack properties, the volume compressibility of rock pores is large and changes along with the change of pressure, so that the volume of the rock pores and the volume of water in the gas reservoir can change along with the progress of exploitation, at the moment, the original geological reserves of natural gas of the gas reservoir are calculated by adopting a conventional gas reservoir material balance method, and the obtained calculation result is greatly different from the actual result.
Disclosure of Invention
Aiming at the defects or shortcomings, the invention provides an evaluation method of the natural gas original geological reserve of a fractured gas reservoir, so that the natural gas original geological reserve of a special fractured gas reservoir can be obtained through more accurate exploration and calculation.
In order to achieve the above object, the present invention provides a method for evaluating the original geological reserves of natural gas of a fractured gas reservoir, wherein the method for evaluating the original geological reserves of natural gas of the fractured gas reservoir comprises:
acquiring the water volume change rate and the rock pore volume change rate;
calculating equivalent apparent pressure according to basic parameters of a gas reservoir, production dynamic data, water volume change rate and rock pore volume change rate;
and determining a functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production according to the equivalent apparent pressure and the corresponding gas reservoir accumulative gas production, and determining the original geological reserve of the natural gas of the gas reservoir according to the functional relation.
In the embodiment of the invention, before the water volume change rate and the rock pore volume change rate are obtained, the method further comprises the steps of counting basic parameters and production dynamic data of the gas reservoir, wherein the basic parameters of the gas reservoir comprise original formation pressure of the gas reservoir, volume compressibility of water, overburden pressure, original reservoir water saturation, pore volume compressibility under zero effective stress and attenuation coefficient of pore pressure changing along with the effective stress; the production dynamic data comprises the current gas reservoir average formation pressure, the current gas compression factor and the gas reservoir accumulated gas production rate.
In an embodiment of the present invention, obtaining the water volume change rate includes:
counting the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir and the volume compression coefficient of water;
and calculating the water volume change rate according to the original formation pressure of the gas reservoir, the current average formation pressure of the gas reservoir and the volume compression coefficient of water.
In the embodiment of the invention, the calculation formula of the water volume change rate is as follows:
wherein epsilonwIs the change rate of the volume of the formation water, and has no dimension; Δ VwIs the volume change of formation water with the unit of 108m3；VwiIs the original formation water volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; cwIs the volume compressibility of water in MPa-1。
In an embodiment of the invention, obtaining the rock pore volume change rate comprises:
counting original formation pressure of the gas reservoir, average formation pressure of the current gas reservoir, overburden pressure, pore volume compression coefficient under zero effective stress and attenuation coefficient of pore pressure changing along with the effective stress;
and calculating the change rate of the rock pore volume according to the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir, the overburden pressure, the pore volume compression coefficient under zero effective stress and the attenuation coefficient of the pore pressure changing along with the effective stress.
In the embodiment of the invention, when the change of the pore volume compression coefficient is considered, the calculation formula of the rock pore volume change rate is as follows:
wherein epsilonpvThe change rate of the rock pore volume is dimensionless; Δ VpIs the volume change of rock pore space, and has the unit of 108m3；VpiIs the original rock pore volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
In the embodiment of the invention, when the change of the pore volume compression coefficient is not considered, the calculation formula of the rock pore volume change rate is as follows:
wherein the content of the first and second substances,
wherein epsilonpcThe change rate of the rock pore volume is dimensionless; cpiThe compression coefficient of the original pore volume of the rock is expressed in MPa-1；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
In the embodiment of the present invention, the calculation formula of the equivalent apparent pressure is:
wherein Y is equivalent apparent pressure in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; z is the current gas compression factor and is dimensionless; swiIs the original reservoir water saturation, fraction; epsilonwIs the change rate of the volume of the formation water, and has no dimension; epsilonpThe change rate of the rock pore volume is dimensionless.
In the embodiment of the invention, the function relation that the equivalent apparent pressure changes along with the gas reservoir accumulated gas production according to the equivalent apparent pressure and the corresponding gas reservoir accumulated gas production comprises the following steps:
calculating values of a plurality of groups of equivalent apparent pressures and counting corresponding values of the gas reservoir accumulative gas production;
and determining a functional relation of the equivalent apparent pressure along with the change of the current gas reservoir accumulative gas production by adopting curve fitting according to the values of the multiple groups of equivalent apparent pressures and the corresponding values of the gas reservoir accumulative gas production.
In the embodiment of the invention, the curve fitting is linear fitting, and the functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production is a linear function.
In the embodiment of the invention, the step of determining the original geological reserves of the natural gas of the gas reservoir according to the first-order function comprises the following steps:
calculating the intercept and the slope of the primary function;
calculating the original geological reserves of the natural gas of the gas reservoir according to the intercept and the slope of the primary function; the calculation formula of the original geological reserves of the natural gas of the gas reservoir is as follows:
wherein G is the original geological reserves of the natural gas of the gas reservoir, a is the absolute value of the slope, and b is the intercept.
Through the technical scheme, the method for evaluating the original geological reserves of the natural gas of the fractured gas reservoir provided by the embodiment of the invention has the following beneficial effects:
when the natural gas original geological reserve of a special fractured gas reservoir is calculated by using the calculating method, the natural gas original geological reserve of the special fractured gas reservoir is calculated by acquiring the water volume change rate and the rock pore volume change rate, calculating the corresponding equivalent apparent pressure under the current gas reservoir average formation pressure by combining the basic parameters and the production dynamic data of the gas reservoir, and determining the relation between the equivalent apparent pressure and the gas reservoir accumulated gas production. The method of the invention considers the change of water volume and rock pore volume in the mining process, converts the pressure of the whole gas reservoir into equivalent apparent pressure, and achieves the purpose of more accurate calculation result when calculating the original geological reserve of the special gas reservoir with crack property by determining the relation between the equivalent apparent pressure and the accumulated gas production.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide an understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention without limiting the invention. In the drawings:
FIG. 1 schematically illustrates a flow chart of steps of a method for evaluating a raw geological reserve of a fractured gas reservoir natural gas in accordance with an embodiment of the invention;
FIG. 2 schematically illustrates a flowchart of step S10 in a method for evaluating a natural gas original geological reserve of a fractured gas reservoir according to an embodiment of the invention;
FIG. 3 schematically illustrates another flowchart of step S10 in a method for evaluating a natural gas original geological reserve of a fractured gas reservoir according to an embodiment of the invention;
FIG. 4 schematically illustrates a flowchart of step S30 in a method for evaluating a natural gas original geological reserve of a fractured gas reservoir according to an embodiment of the invention;
FIG. 5 is a graph of the cumulative gas production G for a gas reservoir after curve fitting in an embodiment in accordance with the inventionpAnd the equivalent apparent pressure Y.
Detailed Description
The following detailed description of specific embodiments of the invention refers to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative and explanatory of the invention and are not restrictive thereof.
The evaluation method of the original geological reserves of natural gas of the fractured gas reservoir according to the invention is described below with reference to the attached drawings.
Fig. 1 schematically shows a flow chart of steps of an evaluation method of natural gas original geological reserves of a fractured gas reservoir according to an embodiment of the invention, and as shown in fig. 1, the invention provides an evaluation method of natural gas original geological reserves of a fractured gas reservoir, wherein the evaluation method of natural gas original geological reserves of a fractured gas reservoir includes the following steps:
step S10: and acquiring the water volume change rate and the rock pore volume change rate.
Wherein the rock pore volume change rate is defined as the ratio of the rock pore volume change amount of the pressure change from the original formation pressure to the current pressure to the original rock pore volume; the formation water volume change rate is defined as the ratio of the amount of change in formation water volume to the original formation water volume at the change in pressure from the original formation pressure to the current pressure.
Step S20: and calculating the equivalent apparent pressure according to the basic parameters of the gas reservoir, the production dynamic data, the water volume change rate and the rock pore volume change rate.
The equivalent apparent pressure is obtained by converting the pressure in the whole gas reservoir into one apparent pressure when the volume change of rock and the volume change of water are considered. When the pressure in the gas reservoir is converted into the equivalent apparent pressure, the influence caused by the reduction of the average pressure of the stratum due to the exploitation of natural gas is considered, and the influence caused by the reduction of the average stratum pressure, the change of the water volume and the change of the rock pore volume is also considered.
Step S30: and determining a functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production according to the equivalent apparent pressure and the corresponding value of the gas reservoir accumulative gas production, and determining the original geological reserve of the natural gas of the gas reservoir according to the functional relation.
When the method is used for calculating the natural gas original geological reserves of special gas reservoirs with abnormal high pressure, crack property and the like, the corresponding equivalent apparent pressure under the current gas reservoir average formation pressure is calculated by acquiring the water volume change rate and the rock pore volume change rate and combining the basic parameters and the production dynamic data of the gas reservoir, and the natural gas original geological reserves of the special gas reservoirs are calculated by determining the relationship between the equivalent apparent pressure and the gas reservoir accumulated gas production. The method converts the pressure of the whole gas reservoir into the equivalent apparent pressure on the basis of considering the volume change of water and the volume change of rock pores, and achieves the aim of more accurate calculation result when calculating the original geological reserves of the special gas reservoir with abnormal high pressure and crack property by determining the relation between the equivalent apparent pressure and the accumulated gas production.
In the embodiment of the present invention, in step S10: before obtaining the water volume change rate and the rock pore volume change rate, the method also comprises the following steps:
step S00: and (5) counting basic parameters and production dynamic data of the gas reservoir.
The basic parameters of the gas reservoir comprise original formation pressure of the gas reservoir, volume compressibility of water, overburden pressure, water saturation of the original reservoir, pore volume compressibility under zero effective stress and attenuation coefficient of pore pressure changing along with the effective stress; the production dynamic data comprises the current gas reservoir average formation pressure, the current gas compression factor and the gas reservoir accumulated gas production rate. The basic parameters of the gas reservoir can be directly measured by an instrument in an exploration stage, and the production dynamic data is recorded by the instrument in real time in the production process, so that the basic parameters and the production dynamic data of the gas reservoir are both parameters which are very easy to obtain, and the measurement is carried out without an additional instrument, thereby facilitating statistics.
Fig. 2 schematically shows a flowchart of step S10 in the method for evaluating the original geological reserve of natural gas from a fractured gas reservoir according to an embodiment of the invention. As shown in fig. 2, in the embodiment of the present invention, the step of acquiring the water volume change rate includes:
s101: counting the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir and the volume compression coefficient of water;
s102: and calculating the water volume change rate according to the original formation pressure of the gas reservoir, the current average formation pressure of the gas reservoir and the volume compression coefficient of water.
When the water volume change rate is calculated, the corresponding water volume change rate under the current gas reservoir average formation pressure can be calculated only by counting the gas reservoir original formation pressure and the water volume compression coefficient in the basic parameters of the gas reservoir and the current gas reservoir average formation pressure in the production dynamic data, and the method is convenient and rapid.
In the embodiment of the invention, the calculation formula of the water volume change rate is as follows:
wherein epsilonwIs the change rate of the volume of the formation water, and has no dimension; Δ VwIs the volume change of formation water with the unit of 108m3；VwiIs the original formation water volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; cwIs the volume compressibility of water in MPa-1。
Fig. 3 schematically shows another flowchart of step S10 in the method for evaluating the original geological reserve of natural gas from a fractured gas reservoir according to an embodiment of the invention. As shown in fig. 3, in the embodiment of the present invention, obtaining the rock pore volume change rate includes:
s103: counting original formation pressure of the gas reservoir, average formation pressure of the current gas reservoir, overburden pressure, pore volume compression coefficient under zero effective stress and attenuation coefficient of pore pressure changing along with the effective stress;
s104: and calculating the change rate of the rock pore volume according to the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir, the overburden pressure, the pore volume compression coefficient under zero effective stress and the attenuation coefficient of the pore pressure changing along with the effective stress.
When the rock pore volume change rate is calculated, the rock pore volume change rate corresponding to the current gas reservoir average formation pressure can be calculated by only counting the gas reservoir original formation pressure, the overlying pressure, the pore volume compression coefficient under the zero effective stress and the attenuation coefficient of the pore pressure changing along with the effective stress in the basic parameters of the gas reservoir and the current gas reservoir average formation pressure in the production dynamic data, so that the rock pore volume change rate is convenient and quick. It should be noted that, in the embodiment of the present invention, steps S101 to S102 may be executed first, steps S103 to S104 may be executed first, or both steps may be executed at the same time.
In the embodiment of the invention, when the change of the pore volume compression coefficient is considered, the calculation formula of the rock pore volume change rate is as follows:
wherein epsilonpvThe change rate of the rock pore volume is dimensionless; Δ VpIs the volume change of rock pore space, and has the unit of 108m3；VpiIs the original rock pore volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
For some abnormally high-pressure fractured gas reservoirs, the rock pore volume changes unevenly with the pressure due to the fact that the rock pore volume compression coefficient changes greatly in the mining process, and the final calculation result can be more accurate by considering the influence caused by the change of the pore volume compression coefficient.
In the embodiment of the invention, when the change of the pore volume compression coefficient is not considered, the calculation formula of the rock pore volume change rate is as follows:
wherein the content of the first and second substances,
wherein epsilonpcThe change rate of the rock pore volume is dimensionless; cpiThe compression coefficient of the original pore volume of the rock is expressed in MPa-1；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
For some common fractured gas reservoirs, in the mining process, the compression coefficient of the rock pore volume is small, and the change of the compression coefficient is small, namely the rock pore volume can be considered to be uniformly changed along with the change of pressure, so that the influence caused by the change of the compression coefficient of the pore volume can be ignored, the difference between the final calculation result and the calculation result considering the change of the compression coefficient of the pore volume is not very large, and meanwhile, the change of the compression coefficient of the pore volume is not required to be considered, so that the calculation process is simplified, and the calculation is more convenient.
In the embodiment of the present invention, the calculation formula of the equivalent apparent pressure is:
wherein Y is equivalent apparent pressure in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; z is the current gas compression factor and is dimensionless; swiIs the original reservoir water saturation, fraction; epsilonwIs the change rate of the volume of the formation water, and has no dimension; epsilonpThe change rate of the rock pore volume is dimensionless; epsilon when considering the change of the compression coefficient of the rock pore volumep＝εpvEpsilon when neglecting the change of the compression coefficient of the rock pore volumep＝εpc。
Fig. 4 schematically shows a flowchart of step S30 in the method for evaluating original geological reserves of natural gas of a fractured gas reservoir according to an embodiment of the present invention, and as shown in fig. 4, in the embodiment of the present invention, determining a functional relation of the equivalent apparent pressure according to the change of the gas reservoir cumulative gas production according to the equivalent apparent pressure and the corresponding value of the gas reservoir cumulative gas production includes:
s301: calculating values of a plurality of groups of equivalent apparent pressures and counting corresponding values of the gas reservoir accumulative gas production;
s302: and determining a functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production by adopting curve fitting according to the values of the multiple groups of equivalent apparent pressures and the corresponding values of the gas reservoir accumulative gas production.
Namely, a function relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production is determined by a curve fitting method, so that the method is more visual and convenient.
In the embodiment of the invention, the curve fitting can be linear fitting, so that the functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production is a linear function. The linear fitting method is used for determining a linear function of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production, so that the modeling is easy to realize on a computer, meanwhile, the accuracy of a calculation result can be ensured through the linear fitting, and of course, curve fitting in other forms can be performed between the equivalent apparent pressure and the gas reservoir accumulative gas production.
In the embodiment of the invention, the step of determining the original geological reserves of the natural gas reservoir according to the linear function formula comprises the following steps:
calculating the intercept and the slope of the primary function expression;
calculating the original geological reserves of the natural gas of the gas reservoir according to the intercept and the slope of the primary function; the calculation formula of the original geological reserves of the natural gas of the gas reservoir is as follows:
wherein G is the original geological reserves of the natural gas of the gas reservoir, a is the absolute value of the slope, and b is the intercept.
The evaluation process of the method for evaluating the original geological reserves of natural gas of fractured gas reservoirs according to the present invention is described below with reference to the first embodiment, and it should be specifically noted that the data in the first embodiment are only for illustration and are not limited.
Example one
1. And counting the basic parameters and the production dynamic data of the gas reservoir, wherein the counted basic parameters and the production dynamic data of the gas reservoir are shown in a table I and a table II.
Table one: gas reservoir base parameters
Table two: production dynamic data
2. Calculating the change rate of the formation water volume
Compression coefficient of volume C of waterwOriginal formation pressure piSubstituting the average formation pressure p of the gas reservoir into a formula:
and obtaining the water body and change rate data corresponding to the current gas reservoir average formation pressure, wherein the concrete data are shown in the third table.
Table three: water body and change rate corresponding to current gas reservoir average stratum pressure
3. Calculating the change rate of the rock pore volume
The pressure p of the original formationiAverage formation pressure p of gas reservoir, and pore volume compressibility coefficient C under zero effective stressp0Overlying pressure pobAnd substituting attenuation coefficient gamma of pore pressure changing along with effective stress into formula
and calculating the rock pore volume change rate under the current gas reservoir average formation pressure when the rock pore volume compression coefficient is considered to change, wherein the specific data is shown in the fourth table.
Table four: rock pore volume change rate under current gas reservoir average formation pressure when rock pore volume compressibility is considered to change
4. Calculating the equivalent apparent pressure of the current gas reservoir under the average formation pressure
Saturation S of original reservoir waterwiAverage formation pressure p of gas reservoir, current gas compression factor Z and formation water volume change rate epsilonwAnd the rate of change of rock pore volume ∈pSubstituting into the formula
Then calculating the corresponding equivalent apparent pressure Y and the corresponding accumulated gas production G under the current gas reservoir average formation pressurepThe data are shown in Table five.
Table five: equivalent apparent pressure and corresponding cumulative gas production
| Gp/108m3 | Y/ |
| 0 | 45.53161111 |
| 0.11114 | 44.86495397 |
| 0.465005 | 43.79428799 |
| 0.913418 | 42.74867001 |
| 1.206347 | 41.93532569 |
| 1.558371 | 40.90972506 |
| 2.134488 | 39.60465619 |
| 2.477423 | 38.96519977 |
| 2.975813 | 37.59623246 |
| 3.32965 | 36.61711662 |
| 3.62139 | 35.98489594 |
| 4.88805 | 33.14621526 |
| 6.481759 | 28.26707793 |
| 7.969425 | 26.31181386 |
| 9.221587 | 23.39373457 |
| 10.42592 | 20.68876405 |
According to the fifth table, the gas production is accumulated by GpThe horizontal axis and the vertical axis are equivalent visual pressure Y, and G is plottedpAnd fitting the scattered points to a straight line according to the relation graph with the Y relation graph, wherein the fitting result is shown in FIG. 5.
As shown in fig. 5, the fitted straight line relation obtained from the calculated data is:
Y＝-2.0986Gp+44.8429。
5. calculating original geological reserves of natural gas in gas reservoir
The Y intercept b of the line was determined to be 44.8429(MPa) and the absolute value a of the slope of the line was determined to be 2.0986(MPa/(10 MPa)8m3)). And (3) calculating to obtain the original natural gas geological reserve of the gas reservoir when the change of the rock pore volume compressibility is considered by applying the formula (6):
in the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "a plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; may be mechanically coupled, may be electrically coupled or may be in communication with each other; they may be directly connected or indirectly connected through intervening media, or they may be connected internally or in any other suitable relationship, unless expressly stated otherwise. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (10)
1. A method for evaluating the original geological reserves of natural gas of a fractured gas reservoir is characterized by comprising the following steps:
acquiring the water volume change rate and the rock pore volume change rate;
calculating equivalent apparent pressure according to basic parameters of a gas reservoir, production dynamic data, the water volume change rate and the rock pore volume change rate;
and determining a functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production according to the equivalent apparent pressure and the corresponding gas reservoir accumulative gas production, and determining the original geological reserves of the natural gas of the gas reservoir according to the functional relation.
2. The method for evaluating the original geological reserve of natural gas from a fractured gas reservoir according to claim 1, further comprising, before obtaining the water volume change rate and the rock pore volume change rate:
counting basic parameters of the gas reservoir and the production dynamic data;
the basic parameters of the gas reservoir comprise original formation pressure of the gas reservoir, volume compressibility of water, overburden pressure, water saturation of the original reservoir, pore volume compressibility under zero effective stress and attenuation coefficient of pore pressure changing along with the effective stress, and the production dynamic data comprise current average formation pressure of the gas reservoir, current gas compressibility and accumulated gas production rate of the gas reservoir.
3. The method of evaluating a fractured gas reservoir natural gas original geological reserve of claim 2, wherein the obtaining the water volume change rate comprises:
counting the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir and the volume compressibility of the water;
calculating the water volume change rate according to the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir and the volume compressibility of the water;
the calculation formula of the water volume change rate is as follows:
wherein epsilonwIs the change rate of the volume of the formation water, and has no dimension; Δ VwIs the volume change of formation water with the unit of 108m3；VwiIs the original formation water volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; cwIs the volume compressibility of water in MPa-1。
4. The method of evaluating a natural gas original geological reserve of a fractured gas reservoir according to claim 2, wherein obtaining the rock pore volume change rate comprises:
counting the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir, the overburden pressure, the pore volume compression coefficient under the zero effective stress and the attenuation coefficient of the pore pressure changing along with the effective stress;
and calculating the change rate of the rock pore volume according to the original formation pressure of the gas reservoir, the average formation pressure of the current gas reservoir, the overburden pressure, the pore volume compression coefficient under the zero effective stress and the attenuation coefficient of the pore pressure changing along with the effective stress.
5. The method for evaluating the original geological reserve of natural gas of a fractured gas reservoir according to claim 4, wherein when the change of the pore volume compressibility is considered, the calculation formula of the change rate of the rock pore volume is as follows:
wherein epsilonpvThe change rate of the rock pore volume is dimensionless; Δ VpIs the volume change of rock pore space, and has the unit of 108m3；VpiIs the original rock pore volume, and has a unit of 108m3；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
6. The method for evaluating the original geological reserve of natural gas of a fractured gas reservoir according to claim 4, wherein when the change of the pore volume compressibility is not considered, the calculation formula of the change rate of the rock pore volume is as follows:
wherein the content of the first and second substances,
wherein epsilonpcThe change rate of the rock pore volume is dimensionless;Cpithe compression coefficient of the original pore volume of the rock is expressed in MPa-1；piThe original formation pressure of the gas reservoir is expressed in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; p is a radical ofobIs the overburden pressure in MPa; cp0Is the pore volume compression coefficient under zero effective stress and has the unit of MPa-1(ii) a Gamma is the attenuation coefficient of pore pressure changing along with effective stress, and is dimensionless.
7. The method for evaluating the original geological reserve of natural gas from a fractured gas reservoir according to claim 2, wherein the calculation formula of the equivalent apparent pressure is as follows:
wherein Y is equivalent apparent pressure in MPa; p is the current average formation pressure of the gas reservoir, and the unit is MPa; z is the current gas compression factor and is dimensionless; swiIs the original reservoir water saturation, fraction; epsilonwIs the change rate of the volume of the formation water, and has no dimension; epsilonpThe change rate of the rock pore volume is dimensionless.
8. The method for evaluating the original geological reserve of natural gas from a fractured gas reservoir according to any one of claims 1 to 7, wherein the step of determining the functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulated gas production according to the equivalent apparent pressure and the corresponding gas reservoir accumulated gas production comprises the following steps:
calculating a plurality of groups of values of the equivalent apparent pressure and counting corresponding values of the gas reservoir accumulative gas production;
and determining the functional relation of the equivalent apparent pressure along with the change of the gas reservoir accumulative gas production by adopting a curve fitting method according to the plurality of groups of values of the equivalent apparent pressure and the corresponding values of the gas reservoir accumulative gas production.
9. The method of claim 8, wherein the curve fit is a linear fit and the functional relationship of the equivalent apparent pressure as a function of the cumulative gas production from the gas reservoir is a linear function.
10. The method of claim 9, wherein determining the reservoir natural gas original geological reserve according to the first order function comprises:
calculating the intercept and the slope of the primary function;
calculating the original geological reserves of the natural gas of the gas reservoir according to the intercept and the slope of the first-order function; the calculation formula of the original geological reserves of the natural gas of the gas reservoir is as follows:
wherein G is the original geological reserves of the natural gas of the gas reservoir, a is the absolute value of the slope, and b is the intercept.
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| CN117929238B (en) * | 2024-03-19 | 2024-05-28 | 西南石油大学 | Method for testing pore volume compression coefficient of hypotonic rock based on gaseous medium |
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