CN110807259A - Shale gas well gas testing opportunity determination method - Google Patents

Shale gas well gas testing opportunity determination method Download PDF

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CN110807259A
CN110807259A CN201911072743.9A CN201911072743A CN110807259A CN 110807259 A CN110807259 A CN 110807259A CN 201911072743 A CN201911072743 A CN 201911072743A CN 110807259 A CN110807259 A CN 110807259A
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stress
fracture
shale gas
crack
rock
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袁发勇
邹顺良
杨加祥
倪方杰
褚晓丹
付莹莹
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Sinopec Oilfield Service Corp
Sinopec Jianghan Petroleum Engineering Co Ltd
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Sinopec Oilfield Service Corp
Sinopec Jianghan Petroleum Engineering Co Ltd
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH OR ROCK DRILLING; MINING
    • E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells

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Abstract

The invention discloses a method for determining gas testing time of a shale gas well, which can determine the well opening time and the well closing time of gas testing after the fracturing of the shale gas well through the elastomechanics parameters of rocks, the maximum circumferential stress at the tip of a crack, the well mouth pressure and the like, thereby achieving the purposes of reducing the flowback rate and improving the productivity of the shale gas well, developing the shale gas more effectively and improving the ultimate recovery ratio.

Description

Shale gas well gas testing opportunity determination method
Technical Field
The invention relates to the technical field of gas testing of shale gas wells, in particular to a method for determining gas testing time of a shale gas well.
Background
My rock gas resource, although abundant, was developed late. The shale gas exploration and development are formally carried out in 2009 in China, the first shale gas evaluation well is a Wen 201 well, and the appearance of the well marks the development of the Chinese shale gas exploration and development and draws a sequence. By 2012, the fracturing gas testing engineering technology of China fully refers to some advanced technologies of foreign countries, so that research and application of horizontal well staged fracturing, gas testing processes and the like are completed, and the cross-over development is realized in China, so that powerful technical support is provided for shale gas exploration and development of China.
In the initiative link of obtaining productivity, shale gas testing and production are important links. After shale gas wells are fractured in a large scale, some wells start blowout gas testing immediately after fracturing, and some wells are selected to be closed appropriately and then blowout gas testing is carried out. According to field tests, for normal-pressure shale gas wells, the well is closed for a certain time after fracturing, and then the well is opened for blowout, so that the flowback rate can be reduced, and the well productivity can be improved to a certain extent. The research shows that one of the main reasons for increasing the production is that after the fracturing pump is stopped, the formation fractures do not stop extending immediately, but continue to extend and extend for a period of time under the action of follow current and large liquid volume pressurization, so that the fracture network area and the fracture reconstruction volume are increased. However, at present, no reliable method is available for determining reasonable well closing time, which can only be determined at will by experience, but the well closing time is long, which can affect the gas testing construction efficiency, the well closing time is short, and the better yield increasing effect can not be achieved.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a method for determining a gas testing time of a shale gas well, which can accurately determine the gas testing time of the shale gas.
In order to solve the technical problems, the technical scheme adopted by the invention specifically comprises the following contents:
a method for determining a gas testing opportunity of a shale gas well comprises the following steps:
s1: acquiring elastic mechanical parameters of the rock by utilizing a triaxial and uniaxial rock compression mechanical experiment and a Brazilian cleavage tensile strength experiment;
s2: determining a maximum circumferential stress of the fracture tip;
s3: when the maximum circumferential stress at the tip of the crack is equal to the tensile strength of the rock, calculating the fluid pressure in the critical crack when the crack stops extending and expanding, namely the critical bottom pressure, by using the maximum circumferential stress and the tensile strength of the rock;
s4: calculating actual bottom hole pressure according to the wellhead pressure;
s5: when the actual bottom hole pressure is equal to the critical bottom hole pressure, the time for opening the test gas of the shale gas is obtained;
s6: and determining the gas testing shut-in time of the shale gas by using the bottom hole pressure, the pressure drop rate and the critical bottom hole pressure when the fracturing pump stops pumping.
Preferably, the elastic mechanical parameter comprises rock tensile strength RmFracture initiation angle theta, fracture curvature radius r and rock temporary crack radius rcCrack angle β, maximum horizontal principal stress vhAnd vertical principal stress vc。
As a preferable method of the above scheme, in step S2, the specific method of determining the maximum circumferential stress of the fracture tip is to determine the maximum circumferential stress v of the fracture tip using fracture mechanics theory based on the elasto-mechanical parameters and fluid pressure parameters of the rock, namely:
Figure BDA0002261466600000021
(ii) a Wherein: t is the stress parallel to the fracture face; and N is the stress perpendicular to the crack surface, the calculation formula of the stress T parallel to the crack surface and the stress N perpendicular to the crack surface is as follows:
Figure BDA0002261466600000022
wherein: p is the fluid pressure in the slot, K1、K2The stress intensity factor of the crack tip is calculated by the following formula:
K1＝-τtr1/2+πτna,K2＝τc(πa)1/2wherein: tau istFor normal stress at fracture face, τnFor fracture surface tangential stress, τcThe three stresses are fracture face shear stress, and the calculation formulas of the three stresses are as follows:
preferably, in step S3, when the maximum circumferential stress at the fracture tip is equal to the rock tensile strength, the fluid pressure P in the fracture is the critical bottom hole pressure PCritical point of。
Preferably, in step S4, the actual bottom hole pressure P isPractice ofThe calculation formula of (2) is as follows: pPractice of＝PWell head+25。
Preferably, in step S6, the calculation formula of the test gas shut-in time t of the shale gas is as follows:
Figure BDA0002261466600000031
wherein: pStopping the pumpIs the bottom hole pressure when the fracturing pump is stopped, PCritical point ofAt the critical bottom hole pressure, γ is the drawdown rate.
Compared with the prior art, the invention has the beneficial effects that:
the invention discloses a method for determining a gas testing time of a shale gas well, which can determine the well opening time and the well closing time of the shale gas well through the elastomechanics parameters of rocks, the maximum circumferential stress at the tip of a crack, the well mouth pressure and the like, thereby achieving the purposes of reducing the flowback rate and improving the productivity of the shale gas well, developing the shale gas more effectively and improving the ultimate recovery ratio.
The foregoing description is only an overview of the technical solutions of the present invention, and in order to make the technical means of the present invention more clearly understood, the present invention may be implemented in accordance with the content of the description, and in order to make the above and other objects, features, and advantages of the present invention more clearly understood, the following preferred embodiments are described in detail with reference to the accompanying drawings.
Drawings
Fig. 1 is a schematic flow chart of a method for determining a gas testing opportunity of a shale gas well according to the present invention.
Detailed Description
To further illustrate the technical means and effects of the present invention adopted to achieve the predetermined objects, the following detailed description of the embodiments, structures, features and effects according to the present invention with reference to the accompanying drawings and preferred embodiments is as follows:
as shown in FIG. 1, the invention discloses a method for determining a gas testing opportunity of a shale gas well, and particularly in the invention, taking a certain block of shale gas well as an example, the middle part of a reservoir is 2577m deep, and the pressure P of a well head is obtained after fracturing is finished and a pump is stoppedWell head for stopping pump32MPa, wellbore fluid density 1g/cm3。
S1: and acquiring the elastic mechanical parameters of the rock by utilizing a triaxial and uniaxial rock compression mechanical experiment and a Brazilian cleavage tensile strength experiment.
In the present invention, the elastic mechanical parameters include rock tensile strength RmFracture initiation angle theta, fracture curvature radius r and rock temporary crack radius rcCrack angle β, maximum horizontal principal stress vhAnd vertical principal stress vc。
Specifically, the values of the elastic mechanical parameters are obtained by utilizing a triaxial and uniaxial rock compression mechanical experiment and a Brazilian split tensile strength experiment, and are specifically shown in table 1:
TABLE 1 elastomechanical parameters
Figure BDA0002261466600000041
S2: the maximum circumferential stress at the fracture tip is determined.
Specifically, in step S2, a specific method of determining the maximum circumferential stress of the fracture tip is to determine the maximum circumferential stress v of the fracture tip using fracture mechanics theory based on the elasto-mechanical parameters and fluid pressure parameters of the rock, namely:
Figure BDA0002261466600000042
wherein: t is the stress parallel to the fracture face; and N is the stress perpendicular to the crack surface, the calculation formula of the stress T parallel to the crack surface and the stress N perpendicular to the crack surface is as follows:
Figure BDA0002261466600000043
wherein: p is the fluid pressure in the slot, K1、K2The stress intensity factor of the crack tip is calculated by the following formula:
K1＝-τtr1/2+πτna,K2＝τc(πa)1/2wherein: tau istFor normal stress at fracture face, τnFor fracture surface tangential stress, τcThe three stresses are fracture face shear stress, and the calculation formulas of the three stresses are as follows:
Figure BDA0002261466600000044
s3: and when the maximum circumferential stress at the tip of the fracture is equal to the tensile strength of the rock, calculating the critical fluid pressure in the fracture when the fracture stops extending and expanding, namely the critical bottom hole pressure, by using the maximum circumferential stress and the tensile strength of the rock.
Specifically, in step S3, when the maximum circumferential stress at the fracture tip is equal to the rock tensile strength, the fluid pressure P in the fracture is the critical bottom hole pressure PCritical point of。
In this example, the maximum circumferential stress v due to the fracture tip and the rock tensile strength RmEqual and in this example the rock tensile strength RmWhen the stress v is 5MPa, the maximum circumferential stress v of the crack tip is 5 MPa; then, using the crack tip stress intensity factor K1And K2Fracture surface normal stress tautFracture surface tangential stress taunFracture surface shear stress τcMaximum of fracture tipCircumferential stress v, initiation angle theta, fracture curvature radius r and rock temporary crack radius rcCrack angle β, maximum horizontal principal stress vhAnd vertical principal stress vcThe value of P is obtained by the formulaCritical point of＝43MPa。
S4: the actual bottom hole pressure is calculated from the wellhead pressure.
In step S4, the actual bottom hole pressure PPractice ofThe calculation formula of (2) is as follows: pPractice of＝PWell head+25。
S5: and when the actual bottom hole pressure is equal to the critical bottom hole pressure, the time for opening the test gas of the shale gas is obtained.
In the present example, when P isPractice ofWhen the pressure of the well head is reduced to 43MPa, namely the well head pressure PWell headAnd when the pressure is 18MPa, the gas testing and well opening time of the shale gas well in the example is obtained.
S6: and determining the gas testing shut-in time of the shale gas well by using the bottom hole pressure, the pressure drop rate and the critical bottom hole pressure when the fracturing pump stops pumping.
Specifically, in step S6, the calculation formula of the test gas shut-in time t of the shale gas well is as follows:
Figure BDA0002261466600000051
wherein: pStopping the pumpIs the bottom hole pressure when the fracturing pump is stopped, PCritical point ofFor the critical bottom hole pressure, γ is the pressure drop rate, in this example, γ is 2MPa/d, PStopping the pump＝PWell head for stopping pumpAnd +25 ═ 57MPa, the gas test shut-in time t of the shale gas well is 7d, that is, in the present example, the gas test shut-in time of the shale gas well is 7 d.
The above embodiments are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited thereby, and any insubstantial changes and substitutions made by those skilled in the art based on the present invention are within the protection scope of the present invention.

Claims (6)

1. A method for determining a gas testing opportunity of a shale gas well is characterized by comprising the following steps:
s1: acquiring elastic mechanical parameters of the rock by utilizing a triaxial and uniaxial rock compression mechanical experiment and a Brazilian cleavage tensile strength experiment;
s2: determining a maximum circumferential stress of the fracture tip;
s3: when the maximum circumferential stress at the tip of the crack is equal to the tensile strength of the rock, calculating the fluid pressure in the critical crack when the crack stops extending and expanding, namely the critical bottom pressure, by using the maximum circumferential stress and the tensile strength of the rock;
s4: calculating actual bottom hole pressure according to the wellhead pressure;
s5: when the actual bottom hole pressure is equal to the critical bottom hole pressure, the time for opening the test gas of the shale gas is obtained;
s6: and determining the gas testing shut-in time of the shale gas by using the bottom hole pressure, the pressure drop rate and the critical bottom hole pressure when the fracturing pump stops pumping.
2. The method for determining the testing time of the shale gas well as in claim 1, wherein the elasto-mechanical parameter comprises rock tensile strength RmFracture initiation angle theta, fracture curvature radius r and rock temporary crack radius rcCrack angle β, maximum horizontal principal stress vhAnd vertical principal stress vc。
3. The shale gas well gas testing opportunity determination method as claimed in claim 2, wherein in step S2, the specific method for determining the maximum circumferential stress at the fracture tip is to determine the maximum circumferential stress v at the fracture tip by using fracture mechanics theory based on the elasto-mechanical parameters and the fluid pressure parameters of the rock, namely:
Figure FDA0002261466590000011
(ii) a Wherein: t is the stress parallel to the fracture face; and N is the stress perpendicular to the crack surface, the calculation formula of the stress T parallel to the crack surface and the stress N perpendicular to the crack surface is as follows:
Figure FDA0002261466590000012
wherein: p is the fluid pressure in the slot, K1、K2The stress intensity factor of the crack tip is calculated by the following formula:
K1＝-τtr1/2+πτna,K2＝τc(πa)1/2wherein: tau istFor normal stress at fracture face, τnFor fracture surface tangential stress, τcThe three stresses are fracture face shear stress, and the calculation formulas of the three stresses are as follows:
Figure FDA0002261466590000021
4. the shale gas well gas testing opportunity determination method as claimed in claim 3, wherein step S3 is that when the maximum circumferential stress at the fracture tip is equal to the tensile strength of the rock, the fluid pressure P in the fracture is the critical bottom hole pressure PCritical point of。
5. The shale gas well gas testing opportunity determination method as claimed in claim 4, wherein in step S4, the actual bottom hole pressure PPractice ofThe calculation formula of (2) is as follows: pPractice of＝PWell head+25。
6. The method for determining the gas testing opportunity of the shale gas well as claimed in claim 1, wherein in step S6, the calculation formula of the gas testing shut-in time t of the shale gas is as follows:
Figure FDA0002261466590000022
wherein: pStopping the pumpIs the bottom hole pressure when the fracturing pump is stopped, PCritical point ofAt the critical bottom hole pressure, γ is the drawdown rate.
CN201911072743.9A 2019-11-05 2019-11-05 Shale gas well gas testing opportunity determination method Pending CN110807259A (en)

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Cited By (2)

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Publication number Priority date Publication date Assignee Title
CN112214904A (en) * 2020-10-20 2021-01-12 西南石油大学 Valve chamber pressure drop rate calculation method under suction condition of gas pipeline compressor
CN117057283A (en) * 2023-10-12 2023-11-14 西南石油大学 Method for judging time spent in shale gas horizontal well oil pipe descending

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CN109800523A (en) * 2019-01-28 2019-05-24 西南石油大学 Nonopiate intrinsic fracture opens determination method under the conditions of a kind of hydraulic fracturing is temporarily stifled
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CN109162701A (en) * 2018-09-12 2019-01-08 西南石油大学 A kind of coal seam open hole well Fracturing Pressure Prediction method
CN109359376A (en) * 2018-10-10 2019-02-19 北京科技大学 Hydraulically created fracture sentences knowledge method in the extension of shale reservoir intrinsic fracture interface
CN109800523A (en) * 2019-01-28 2019-05-24 西南石油大学 Nonopiate intrinsic fracture opens determination method under the conditions of a kind of hydraulic fracturing is temporarily stifled
CN109933845A (en) * 2019-01-28 2019-06-25 西南石油大学 A kind of unlatching range computation method of intrinsic fracture when temporarily stifled pressure break

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112214904A (en) * 2020-10-20 2021-01-12 西南石油大学 Valve chamber pressure drop rate calculation method under suction condition of gas pipeline compressor
CN117057283A (en) * 2023-10-12 2023-11-14 西南石油大学 Method for judging time spent in shale gas horizontal well oil pipe descending
CN117057283B (en) * 2023-10-12 2024-01-26 西南石油大学 Method for judging time spent in shale gas horizontal well oil pipe descending

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Application publication date: 20200218