Natural gas reservoir formation pressure field evaluation method

Abstract

The invention discloses a natural gas reservoir formation pressure field evaluation method, and belongs to the technical field of gas reservoir development. According to the method disclosed by the invention, a formation pressure prediction method under the condition of no formation pressure test data is adopted, a formation pressure evaluation system of a gas field (or a block) is perfected, the formation pressure is comprehensively evaluated, and inter-well formation pressure field distribution calculation is realized; in the stable stage of the gas field, the most effective reference is provided for well pattern perfection or encryption potential evaluation; for a newly-put-into-production gas well, the workload of stratum testing can be reduced or even eliminated, and the method has a good application prospect; meanwhile, the method can be used for evaluating the actual use degree and determining the later encryption potential.

Description

Technical Field

[0001] The invention belongs to the technical field of gas reservoir development, and in particular relates to a method for evaluating a formation pressure field of a natural gas reservoir. Background Art

[0002] In the field of gas reservoir development technology, natural gas resources flow from underground through wellbore to the surface through engineering drilling, and then are transported to major cities and gas-using sites. The pressure and production of natural gas wells are direct indicators of the production capacity of gas wells. Similarly, formation pressure is the most direct indicator of gas reservoir dynamics. The dynamic analysis of gas wells (or gas reservoirs) based on pressure and production is the core of gas field development management and runs through the entire gas field development process.

[0003] In actual work, the commonly used methods for evaluating the formation pressure of a gas well include single-point pressure gauge testing, wellhead pressure conversion and theoretical calculation, which can clearly grasp the formation pressure at the gas well location and further calculate the geological reserves of the gas well. For the remaining reserves between two or more natural gas wells, it is realized by calculating the average parameters of formation physical properties or geological model operations, but the actual degree of production cannot be evaluated, the potential for later densification is unclear, and the internal rate of return after densification cannot be guaranteed. Summary of the invention

[0004] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a method for evaluating the formation pressure field of a natural gas reservoir, so as to solve the technical problems that the existing evaluation methods cannot evaluate the actual degree of utilization, the potential for later densification is unclear, and the internal rate of return after densification cannot be guaranteed.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention discloses a method for evaluating a formation pressure field of a natural gas reservoir, comprising the following steps:

[0007] S1: Carry out dynamic analysis and demonstration of connectivity between the exciting wells and the observation wells in the interference test well group to obtain the binomial production capacity equation of the exciting wells;

[0008] S2: Then, the abandoned production capacity equation of the excited well is established according to the binomial production capacity equation of the excited well, and the abandoned formation pressure is calculated;

[0009] S3: Calculate the interwell pressure between the exciting well and the observation well when the exciting well is abandoned based on the abandoned formation pressure.

[0010] Further, in S1, the binomial production capacity equation of the exciting well is as follows:

[0011]

[0012] in:

[0013]

[0014]

[0015] P wf P is the production flow pressure of the exciting well; r is the formation pressure; q is the production of the excitation well; A and B are the coefficients of the binomial production capacity equation of the excitation well; D is the transition parameter;

[0016] is the gas deviation factor; T is the bottom hole temperature; k is the interpreted permeability of the interference test well group; h is the formation thickness of the exciting well; μ g is the gas viscosity; r w is the wellbore radius; is the average porosity of the excited well; q g is the production of the excited well; q is the conventional production.

[0017] Furthermore, in S2, the process of establishing the abandoned production capacity equation of the excited well according to the binomial production capacity equation of the excited well is as follows:

[0018] If the reservoir properties do not change during the production process, the seepage equation shows that at any stage, the coefficients A and B of the binomial production equation of the excited well are only related to the deviation factor and viscosity, and the following formula is obtained:

[0019]

[0020] Right now,

[0021] Among them: A 废弃 A is the binomial capacity coefficient when abandoned; B 废弃 is the binomial capacity coefficient B when abandoned; μ g is the gas viscosity; is the gas deviation factor; P 废弃 is the abandoned formation pressure; q 废弃 The yield at the time of abandonment; is the gas viscosity at the time of disposal.

[0022] Furthermore, the reservoir properties include temperature, formation coefficient and skin coefficient.

[0023] Furthermore, in S2, the abandoned formation pressure is calculated by the following formula:

[0024]

[0025] Among them, P 废弃 is the abandoned formation pressure; P wf废弃 is the flow pressure at the time of disposal.

[0026] Furthermore, in S3, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated based on the abandoned formation pressure, including two cases: not considering interference and considering interference.

[0027] Further, when the interference is not considered, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated according to the abandoned formation pressure, including the following steps:

[0028] According to the gas differential equation, the pressure expression at any point between wells is:

[0029]

[0030] Where: P is the interwell pressure between the exciting well and the observation well when the exciting well is abandoned; P e is the formation boundary pressure; P ω is the bottom flow pressure of the abandoned well; r w is the wellbore radius; r e is the formation leakage radius.

[0031] Furthermore, when interference is taken into account, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated based on the superposition principle.

[0032] Further, according to the superposition principle, the following steps are included to calculate:

[0033] When the observation well and the exciting well are producing at the same time, the pressure drop at any point between the wells is equal to the sum of the pressure drops at that location when the two wells are producing separately.

[0034] Furthermore, in S1, the interference test well group preferably statically confirms that there is a possibility of formation connectivity and the well network is regular and complete.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] The present invention discloses a method for evaluating the formation pressure field of a natural gas reservoir. By adopting a formation pressure prediction method without formation pressure test data, the formation pressure evaluation system of the gas field (or block) is improved, all-round evaluation of formation pressure is achieved, and calculation of the distribution of formation pressure field between wells is realized. In the stable stage of the gas field, the most effective reference is provided for the improvement of the well network or the evaluation of the infill potential. For newly-commissioned gas wells, the workload of formation testing can be reduced or even eliminated, and the method has good application prospects. At the same time, the method can be used to evaluate the actual production degree and clarify the potential for later infilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the formation pressure profile between wells X1 and X2 in Example 1;

[0038] Figure 2 Schematic diagram of the formation pressure profile between wells X1 and X2 at different production rates in Example 2. DETAILED DESCRIPTION

[0039] In order to enable those skilled in the art to understand the characteristics and effects of the present invention, the following is a general description and definition of the terms and expressions mentioned in the specification and claims. Unless otherwise specified, all technical and scientific terms used in the text are the common meanings understood by those skilled in the art for the present invention. In the event of a conflict, the definition in this specification shall prevail.

[0040] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0041] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0042] The present invention provides a method for evaluating the formation pressure field of a natural gas reservoir, which specifically comprises the following steps:

[0043] 1) Prefer statically confirming the possibility of formation connectivity, regular well pattern and perfect blocks, setting interference test well groups; tracking and observing well pressure changes;

[0044] 2) Carry out dynamic analysis and demonstration of connectivity between the exciting wells and the observation wells in the well group;

[0045] 3) Obtaining binomial production capacity equation of the excited well;

[0046] A: For connected well groups, the average permeability between wells is interpreted using interference well tests;

[0047] B: According to the average permeability between wells calculated in A, calculate B and A in the binomial productivity equation of the excited wells in the well group, and then obtain the binomial productivity equation of the excited wells:

[0048]

[0049]

[0050]

[0051]

[0052] Pwf P is the production flow pressure of the exciting well; r is the formation pressure; q is the production of the excitation well; A and B are the coefficients of the binomial production capacity equation of the excitation well respectively;

[0053] μ g is the gas viscosity; is the gas deviation factor; T is the bottom hole temperature; k is the interpreted permeability of the interference test well group; h is the formation thickness of the exciting well; μ is the gas viscosity; r w is the wellbore radius; is the average porosity of the excited well; q g To stimulate well production.

[0054] 4) Obtaining binomial production capacity equation of the excited well;

[0055] A. Use the vertical pipe flow method, combined with the wellhead oil pressure, to calculate the abandoned flow pressure of the gas well;

[0056] B. Determine the waste capacity equation;

[0057] Assuming that the reservoir properties (temperature, formation coefficient, skin coefficient) do not change during the production process, it can be seen from the seepage equation that at any stage, the A and B values ​​of its production capacity equation are only related to the deviation factor and viscosity.

[0058]

[0059] Right now,

[0060] Among them: A 废弃 A is the binomial capacity coefficient when abandoned; B 废弃 is the binomial capacity coefficient B when abandoned; μ g is the gas viscosity; is the gas deviation factor; P 废弃 is the abandoned formation pressure; q 废弃 The yield at the time of abandonment; is the gas viscosity at the time of disposal;

[0061] C. Calculate the pressure of abandoned formations

[0062] After obtaining the abandonment equation, the abandoned formation pressure is calculated according to the abandoned production capacity equation:

[0063]

[0064] Where P 废弃 is the abandoned formation pressure; P wf废弃 is the flow pressure at the time of disposal;

[0065] 5) Calculate the interwell pressure (interwell pressure drop funnel) between the exciting well and the observation well when the exciting well is abandoned;

[0066] A. Don’t consider interference

[0067] According to the gas differential equation (steady flow), the pressure expression at any point is:

[0068]

[0069] Where: P is the interwell pressure between the exciting well and the observation well when the exciting well is abandoned; P e is the formation boundary pressure; P ω is the bottom flow pressure of the abandoned well; r w is the wellbore radius; r e is the formation leakage radius;

[0070] B. When interference is considered, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated based on the abandoned formation pressure, including the following steps:

[0071] According to the superposition principle, when the observation well and the exciting well are producing at the same time, the pressure drop at any point between the wells is equal to the sum of the pressure drops at that location when the two wells are producing separately.

[0072] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0073] Example 1

[0074] For a gas zone with boundary restrictions, when the pressure change reaches the boundary, or when the formation pressure change enters a quasi-stable state, the relationship between the pressure difference and the production is expressed as:

[0075]

[0076] For a closed reservoir, when the production well produces at a constant rate to a plane radial flow, the pressure P at a distance r from the wellbore satisfies the following formula:

[0077]

[0078] Divide formula (1-1) by formula (1-2) to obtain the following formula:

[0079]

[0080]

[0081] S a It is usually obtained through system well testing. It can be regarded as a variable value during the research process.a The pressure distribution of the value is compared with the interference well test results to determine:

[0082] X1 well measured pressure: 9.10MPa;

[0083] X2 well measured pressure: 22.26MPa;

[0084] With S a When is equal to 0.8, the simulated pressure distribution among wells is similar.

[0085] In actual production, the exciting well and the producing well are usually produced at the same time. At this time, the pressure drop at any point (R) between the wells is equivalent to the sum of the pressure drops of the two wells producing separately at that location, P1+P2.

[0086]

[0087]

[0088] The schematic diagram of the inter-well pressure profile between X1 and X2 is shown in Figure 1 shown.

[0089] Example 2

[0090] Taking well X1 as an example, the formation pressure under different production rates of the well is simulated and calculated. 4 m 3 / d, 0.08*10 4 m 3 / d, 0.10*10 4 m 3 / d, 0.20*10 4 m 3 / d, 0.30*10 4 m 3 / d production to abandonment, the abandonment pressure is shown in Table 1. According to the simulation of different production rates, the formation pressure profile between wells X1-X2 is as follows Figure 2 shown.

[0091] Table 1 Abandonment pressure values ​​from production to disposal at different outputs

[0092] <![CDATA[Q(10 4 m 3 / d)]]> pr(MPa) <![CDATA[A new (MPa 2 / (10 4 m 3 / d))]]> <![CDATA[(B new (MPa 2 ) / (10 4 m 3 / d)2]]> 0.05 5.129 266.891 0.139 0.08 5.860 267.302 0.139 0.10 6.278 264.491 0.137 0.20 8.160 268.132 0.136 0.30 9.725 271.996 0.136

[0093] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating formation pressure field of a natural gas reservoir, characterized in that: The following steps are involved: S1: Carry out dynamic analysis and demonstration of connectivity between the exciting wells and the observation wells in the interference test well group to obtain the binomial production capacity equation of the exciting wells; S2: Then, the abandoned production capacity equation of the excited well is established according to the binomial production capacity equation of the excited well, and the abandoned formation pressure is calculated; S3: Calculate the interwell pressure between the exciting well and the observation well when the exciting well is abandoned based on the abandoned formation pressure.

2. A method for evaluating formation pressure field of a natural gas reservoir according to claim 1, characterized in that: In S1, the binomial production capacity equation of the exciting well is as follows: in: P wf P is the production flow pressure of the exciting well; r is the formation pressure; q is the production of the excitation well; A and B are the coefficients of the binomial production capacity equation of the excitation well; D is the transition parameter; is the gas deviation factor; T is the bottom hole temperature; k is the interpreted permeability of the interference test well group; h is the formation thickness of the exciting well; μ g is the gas viscosity; r w is the wellbore radius; is the average porosity of the excited well; q g is the production of the excited well; q is the conventional production.

3. A method for evaluating formation pressure field of a natural gas reservoir according to claim 2, characterized in that: In S2, the process of establishing the abandoned production capacity equation of the excited well according to the binomial production capacity equation of the excited well is as follows: If the reservoir properties do not change during the production process, the seepage equation shows that at any stage, the coefficients A and B of the binomial production equation of the excited well are only related to the deviation factor and viscosity, and the following formula is obtained: Right now, Among them: A 废弃 A is the binomial capacity coefficient when abandoned; B 废弃 is the binomial capacity coefficient B at the time of abandonment; μ g is the gas viscosity; is the gas deviation factor; P 废弃 is the abandoned formation pressure; q 废弃 The yield at the time of abandonment; is the gas viscosity at the time of disposal.

4. A method for evaluating formation pressure field of a natural gas reservoir according to claim 3, characterized in that: The reservoir properties include temperature, formation coefficient and skin coefficient.

5. A method for evaluating formation pressure field of a natural gas reservoir according to claim 3, characterized in that: In S2, the abandoned formation pressure is calculated by the following formula: Among them, P 废弃 is the abandoned formation pressure; P wf废弃 is the flow pressure at the time of disposal.

6. A method for evaluating formation pressure field of a natural gas reservoir according to claim 5, characterized in that: In S3, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated according to the abandoned formation pressure, including two cases of not considering interference and considering interference.

7. A method for evaluating formation pressure field of a natural gas reservoir according to claim 6, characterized in that: When interference is not considered, the interwell pressure between the exciting well and the observation well when the exciting well is abandoned is calculated according to the abandoned formation pressure, including the following steps: According to the gas differential equation, the pressure expression at any point between wells is: Where: P is the interwell pressure between the exciting well and the observation well when the exciting well is abandoned; P e is the formation boundary pressure; P ω is the bottom flow pressure of the abandoned well; r w is the wellbore radius; r e is the formation leakage radius.

8. A method for evaluating formation pressure field of a natural gas reservoir according to claim 6, characterized in that: When interference is taken into account, the interwell pressure between the exciting well and the observation well is calculated based on the superposition principle when the exciting well is abandoned.

9. A method for evaluating formation pressure field of a natural gas reservoir according to claim 8, characterized in that: According to the superposition principle, the calculation includes the following steps: When the observation well and the exciting well are producing at the same time, the pressure drop at any point between the wells is equal to the sum of the pressure drops at that location when the two wells are producing separately.

10. A method for evaluating formation pressure field of a natural gas reservoir according to claim 1, characterized in that: In S1, the interference test well group is preferably a block where the possibility of formation connectivity is confirmed statically and the well pattern is regular and complete.

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