CN108959687B - Evaluation method for repeated fracturing of shale gas horizontal well - Google Patents
Evaluation method for repeated fracturing of shale gas horizontal well Download PDFInfo
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- CN108959687B CN108959687B CN201810345231.4A CN201810345231A CN108959687B CN 108959687 B CN108959687 B CN 108959687B CN 201810345231 A CN201810345231 A CN 201810345231A CN 108959687 B CN108959687 B CN 108959687B
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/20—Design optimisation, verification or simulation
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- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP 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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- E21B43/26—Methods for stimulating production by forming crevices or fractures
Abstract
The invention discloses an evaluation method for shale gas horizontal well repeated fracturing, and belongs to the technical field of yield increase of oil and gas reservoirs. The method comprises the following steps: respectively determining the value of the evaluation index of each well to be evaluated in the n wells to be evaluated; the well to be evaluated is a fractured shale gas horizontal well, and the evaluation indexes comprise the reservoir quality, the well completion quality and the production dynamics of the well to be evaluated; calculating a normalized value of the evaluation index of each well to be evaluated; according to the formula
Calculating a repeated fracturing evaluation value of each well to be evaluated; RF (radio frequency)iEvaluation of repeated fractures for the ith well under evaluation, RiValue of reservoir quality for the ith well to be evaluated, CiValue of completion quality for the ith well to be evaluated, PiFor the value of the production dynamics of the ith well to be evaluated,
and
are each Ri、CiAnd PiI is an integer, i is more than or equal to 1 and less than or equal to n, and 2 is more than or equal to n. The method can quantitatively evaluate the repeated fracturing of the shale gas horizontal well, and effectively overcomes the defect of high subjectivity of an evaluation result caused by setting the weight according to experience.
Description
Technical Field
The invention relates to the technical field of yield increase of oil and gas reservoirs, in particular to an evaluation method for repeated fracturing of a shale gas horizontal well.
Background
At present, a horizontal well and volume fracturing technology is a key technology for efficiently developing shale gas. Along with the multi-batch production of the fractured shale gas horizontal well, the production effects of the fractured wells under the same geological condition show great difference. The foreign shale gas development experience shows that repeated fracturing is an effective means for improving the production effect for the fracturing well with poor production effect. Re-fracturing is a way to perform fracturing operations again or multiple times on the basis of the original fractured well. One important factor in determining the ability of a fractured well to successfully increase production after repeated fracturing is the condition of the fractured well prior to repeated fracturing. It can be said that selecting an appropriate frac well for re-fracturing is the first step in the success of re-fracturing.
The existing well selection method generally adopts a fuzzy evaluation method, and the method comprises the following steps.
Firstly, determining a plurality of evaluation factors capable of measuring the condition of the fractured well, and setting the weight of each evaluation factor. For example, the evaluation factors may include 8 parameters of permeability, porosity, water saturation, skin factor, effective thickness, formation pressure, daily production and differential production pressure of the fractured well, and the evaluation factors are weighted by 0.18, 0.12, 0.09, 0.14 and 0.12 in sequence.
Secondly, n fracture wells m to be selected are determined1、m2、…、mn-1And mnAnd obtain eachThe value of the evaluation factor of each fracturing well to be selected.
Thirdly, calculating the relative membership degree of the evaluation factors according to a fuzzy mathematical theory.
Then, the relative membership degree of the evaluation factors is corrected according to the set weight. The correction formula is as followsij＝wij*aij(i-1, 2, …, n-1 or n, j-1, 2, …, 7 or 8). a isijIs the relative membership, w, of the jth evaluation factor of the ith candidate fracturing wellijThe weight of the jth evaluation factor of the ith candidate fracturing well, bijAnd the corrected value of the relative membership of the j evaluation factor of the ith selected fracturing well.
And finally, adding the relative membership degrees of the corrected evaluation factors contained in each fracturing well to be selected to obtain the comprehensive membership degree of each fracturing well, and judging the quality of each fracturing well according to the magnitude of the comprehensive membership degree.
In the process of implementing the invention, the inventor finds that the prior art has at least the following problems: the weight of the evaluation factor is manually set according to experience, so that the evaluation factor has obvious subjectivity, influences the evaluation result and has certain limitation in application.
Disclosure of Invention
In order to solve the problem that in the prior art, due to the fact that the weight of evaluation factors is artificially set, the evaluation result is influenced, and the application of the evaluation method is limited, the embodiment of the invention provides an evaluation method for shale gas horizontal well repeated fracturing. The technical scheme is as follows:
respectively determining the value of the evaluation index of each well to be evaluated in n wells to be evaluated; the well to be evaluated is a fractured shale gas horizontal well, and the evaluation indexes comprise reservoir quality, completion quality and production dynamics of the well to be evaluated;
calculating a normalized value of the evaluation index of each well to be evaluated;
calculating the repeated fracturing evaluation value of each well to be evaluated according to the following formula;
wherein, RFiA repeated fracture evaluation value R for the ith well to be evaluatediValue of reservoir quality for the ith well under evaluation, CiIs the value of the completion quality of the ith well to be evaluated, PiFor the value of the production dynamics of the ith well under evaluation,
and
are respectively the RiThe C isiAnd said PiI is an integer, i is more than or equal to 1 and less than or equal to n, and 2 is more than or equal to n.
Preferably, the determining the value of the evaluation index of each well to be evaluated includes:
determining a value of a dependent sub-metric for each of the evaluation metrics; the subordinate sub-indexes of the reservoir quality comprise a target body position and a good-quality reservoir drilling length of a well to be evaluated, the subordinate sub-indexes of the well completion quality comprise a primary fracturing non-fractured section length, a primary fracturing sand adding strength and a primary fracturing fluid strength, and the subordinate sub-indexes of the production dynamics comprise a current accumulated gas production rate, a predicted final recoverable reserve, a current pressure level and a current yield level;
and calculating to obtain the value of the evaluation index of each well to be evaluated according to the determined value of the subordinate sub-index of each evaluation index.
Preferably, the reservoir quality of the ith well to be evaluated is calculated by adopting the following formula:
wherein RLiFor the value of the premium reservoir drilling length, RP, of the ith well to be evaluatediThe value of the target body position of the ith well to be evaluated.
Preferably, the completion quality of the ith well to be evaluated is calculated by adopting the following formula:
wherein, CLiFor the value of the initial fracture uncrushed section length, CS, of the ith well to be evaluatediFor the value of the primary fracture sand addition intensity, CW, of the ith well to be evaluatediAnd the value of the strength of the primary fracturing fluid of the ith well to be evaluated.
Preferably, the production dynamics of the ith well to be evaluated is calculated by adopting the following formula:
wherein, PCiFor the value of the cumulative gas production of the ith well to be evaluated, PEiFor the predicted final recoverable reserve value, PP, for the ith said well under evaluationiFor the value of the current pressure level of the ith well to be evaluated, PGiThe value of the current production level of the well to be evaluated is the ith well to be evaluated.
Preferably, the determining the value of the subordinate sub-metric of each of the evaluation metrics includes:
collecting the actual value of the subordinate sub-index of each well to be evaluated;
preprocessing the acquired actual values of the subordinate sub-indexes to obtain corrected values of the subordinate sub-indexes of each well to be evaluated; the correction value of each of the dependent sub-indices is not less than 0 and not more than 1.
Preferably, the preprocessing the collected actual values of the dependent sub-indicators includes:
when min (x)ij) And max (x)ij) When the j (th) subordinate sub-index is not equal and is the first subordinate sub-index, the j (th) subordinate sub-index is the first subordinate sub-index according to a formula
For the jth slavePreprocessing the actual values of the sub-indexes; the first subordinate sub-indicator comprises the target body position, the premium reservoir drilling length, the primary fracture unpressurized section length and the current pressure level;
when min (x)ij) And max (x)ij) When the j (th) subordinate sub-index is not equal and the j (th) subordinate sub-index is not the first subordinate sub-index, according to a formula
Preprocessing the actual value of the jth subordinate sub-index;
when min (x)ij) And max (x)ij) When the j sub indexes are equal, setting the correction values of the j sub indexes of all the wells to be evaluated as 0;
wherein x isijThe actual value y of the j-th subordinate sub index of the ith well to be evaluatedijA corrected value, max (x), of the jth subordinate sub-index of the ith well to be evaluatedij) The maximum value of the j actual values of the subordinate sub indexes of all the wells to be evaluated; min (x)ij) The minimum value is the actual value of the jth subordinate sub-index of all the wells to be evaluated.
Preferably, the acquiring of the actual value of the target body position of each well to be evaluated comprises:
and acquiring the passing proportion of the horizontal section of the well to be evaluated in the optimal target body as an actual value of the position of the target body.
Preferably, the normalized value of the reservoir quality of the ith well to be evaluated adopts a formula
The calculation results in that,
the normalized value of the completion quality of the ith well to be evaluated adopts a formula
The calculation results in that,
the normalized value of the production dynamics of the ith well to be evaluated adopts a formula
The calculation results in that,
wherein max (r) is the maximum value among the reservoir qualities of all the wells to be evaluated, min (r) is the minimum value among the reservoir qualities of all the wells to be evaluated, max (c) is the maximum value among the completion qualities of all the wells to be evaluated, min (c) is the minimum value among the completion qualities of all the wells to be evaluated, max (p) is the maximum value among the production dynamics of all the wells to be evaluated, and min (p) is the minimum value among the production dynamics of all the wells to be evaluated.
Preferably, the method further comprises:
selecting at least one well to be evaluated for repeated fracturing; and the selected at least one repeated fracture evaluation value of the well to be evaluated is higher than the repeated fracture evaluation values of the unselected wells to be evaluated.
The technical scheme provided by the embodiment of the invention has the following beneficial effects:
determining the value of an evaluation index of each well to be evaluated; calculating a normalized value of the evaluation index of each well to be evaluated; according to the formula
Calculating a repeated fracturing evaluation value of each well to be evaluated; the formula is obtained based on a mutation theory, has certain scientific guidance, can quantitatively evaluate the repeated fracturing of the shale gas horizontal well, and effectively overcomes the defect of high subjectivity of an evaluation result caused by setting weight according to experience when evaluating the repeated fracturing.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a method for evaluating shale gas horizontal well re-fracturing provided by an embodiment of the present invention;
FIG. 2 is a flow chart of yet another method for evaluating shale gas horizontal well re-fracturing provided by embodiments of the present invention;
FIG. 3 is a flow chart of another method for evaluating shale gas horizontal well repeated fracturing provided by embodiments of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Fig. 1 illustrates an evaluation method for shale gas horizontal well repeated fracturing provided by an embodiment of the invention, and the method comprises the following steps.
Step 101: and respectively determining the value of the evaluation index of each well to be evaluated in the n wells to be evaluated.
Wherein the well to be evaluated is a shale gas horizontal well which is fractured. For example, the well to be evaluated may be a shale gas horizontal well that has been fractured once.
The evaluation indexes comprise reservoir quality, well completion quality and production dynamics of the well to be evaluated. The reservoir quality may refer to the reservoir innate basic conditions of the well to be evaluated, the completion quality may refer to the reformation effect of the primary fracturing of the well to be evaluated, and the production dynamics may refer to the current production situation of the well to be evaluated.
Step 102: and calculating the normalized value of the evaluation index of each well to be evaluated.
Optionally, the normalized value of the evaluation index k of the ith well to be evaluated may be a ratio of k of the ith well to be evaluated to the sum of k of all wells to be evaluated. k is reservoir quality, completion quality or production dynamics. i is an integer, i is more than or equal to 1 and less than or equal to n, and 2 and less than or equal to n. For example, assuming a total of 6 wells to be evaluated, the completion quality of the 6 wells to be evaluated has values of 0.680, 0.644, 0.317, 0.643, 0.511, and 0.578 in this order. Then, the sum of the completion quality of the 6 wells to be evaluated is 3.193-0.680 +0.644+0.317+0.643+0.511+0.578, the normalized value of the completion quality of the 1 st well to be evaluated is 0.213-0.680/3.193, and the 2 nd well to be evaluated isThe normalized value of completion quality of (a) is 0.202-0.644/3.193, and so on. It should be noted that, in the embodiment of the present invention, the normalization manner of Ri, Ci, and Pi is not limited, and the foregoing normalization manner is only used for illustration, and other normalization manners may also be used to calculate
And
step 103: and (3) calculating the repeated fracture evaluation value of each well to be evaluated according to the formula (1).
Wherein, RFiEvaluation of repeated fractures for the ith well under evaluation, RiValue of reservoir quality for the ith well to be evaluated, CiValue of completion quality for the ith well to be evaluated, PiFor the value of the production dynamics of the ith well to be evaluated,
and
are each Ri、CiAnd PiThe normalized value of (a).
The formula (1) is obtained based on a mutation theory, and the mutation theory can predict the system behavior of mutation and has scientific guidance. Specifically, since the number of evaluation indexes is 3, a dovetail mutation model involving prediction of a 3-variable system can be selected. Further, after the dovetail mutation model is selected, the influence degree of 3 evaluation indexes on the repeated fracture evaluation value needs to be determined, so that the influence degree of each variable in the dovetail mutation model on the future system behavior is determined. The reservoir quality is a prerequisite, the reserve basis of a single well is determined, and the reservoir quality is the most important index required to be considered for the repeated fracturing evaluation; the well completion quality represents whether the primary fracturing reformation of the reservoir is sufficient or not, reflects the potential of improving the yield of a single well by repeated fracturing, and is a secondary important index required to be considered for repeated fracturing evaluation. Thus, the specific formula (1) is obtained by determining the influence degrees of the 3 evaluation indexes from high to low, namely the reservoir quality, the well completion quality and the production dynamics. Therefore, the repeated fracture evaluation value calculated according to the formula (1) meets the actual evaluation requirement, and the accuracy is very high.
Wherein, the larger the repeated fracture evaluation value of a certain well to be evaluated is, the more suitable the well to be evaluated is for repeated fracturing.
The method comprises the steps of determining the value of an evaluation index of each well to be evaluated; calculating a normalized value of the evaluation index of each well to be evaluated; according to the formula
Calculating a repeated fracturing evaluation value of each well to be evaluated; the formula is obtained based on a mutation theory, has certain scientific guidance, can quantitatively evaluate the repeated fracturing of the shale gas horizontal well, and effectively overcomes the defect of high subjectivity of an evaluation result caused by setting weight according to experience when evaluating the repeated fracturing.
FIG. 2 illustrates another evaluation method for shale gas horizontal well repeated fracturing provided by the embodiment of the invention. In contrast to the evaluation method shown in fig. 1, the evaluation method shown in fig. 2 will describe how to obtain the value of the evaluation index for each well to be evaluated, and provide yet another normalization of Ri, Ci, and Pi. Referring to fig. 2, the method includes the following steps.
Step 201: the values of the subordinate sub-indices of each evaluation index are determined.
The subordinate sub-indexes of the reservoir quality comprise the target body position of the well to be evaluated and the drilling length of the high-quality reservoir. The position of the target body and the drilling length of the high-quality reservoir jointly determine the basic geological condition of a single well, and the target body and the drilling length of the high-quality reservoir are important influence factors of gas well productivity.
Subordinate sub-indicators of completion quality include primary frac uncrushed length, primary frac sanded strength, and primary frac fluid strength. The initial fracturing uncrushed section length is the section length of the uncrushed part abandoned for various reasons during the initial fracturing. Specifically, the initial fracture unpressurized section length of the well to be evaluated may be a difference between the horizontal section length of the well to be evaluated and the initial fracture reformed section length. This portion of the interval contributes substantially no to production and can be effectively used if the modification of this portion of the interval is effected by repeated fracturing.
The primary fracturing sand adding strength of the well to be evaluated can be the ratio of the using amount of the proppant to the length of the primary fracturing modification section during primary fracturing of the well to be evaluated. The strength of the primary fracturing fluid of the well to be evaluated can be the ratio of the amount of the fracturing fluid used in primary fracturing of the well to be evaluated to the length of the primary fracturing reconstruction section. The well with lower strength of the primary fracturing fluid and lower strength of the primary fracturing sand adding can also enlarge the transformation range and improve the fracture conductivity in the area by improving the transformation strength, thereby improving the yield of a single well.
Dependent sub-indicators of production dynamics include current accumulated gas production, predicted final recoverable Reserves (EUR), current pressure level and current production level. The current accumulated gas production rate and the current EUR respectively represent the production degree of the gas well in the current state and the final production degree. Repeated fracturing primarily selects wells with lower current production to reduce risk; in addition, in order to effectively carry out flowback and production in the later period, sufficient energy of a gas reservoir must be ensured, so that a well with low pressure is not suitable for repeated fracturing.
Step 202: and calculating to obtain the value of the evaluation index of each well to be evaluated according to the determined value of the subordinate sub-index of each evaluation index.
And (3) calculating the reservoir quality of the ith well to be evaluated by adopting a formula (2).
Wherein RLiValue of the length of the premium reservoir drilling for the ith well to be evaluated, RPiIs the value of the target body position of the ith well to be evaluated.
Wherein, the formula (2) is obtained based on a cusp mutation model. The cusp mutation model can predict the system behavior of two variables. From the formula (2), the value of the drilling length of the high-quality reservoir has a larger influence on the value of the reservoir quality, and the value of the target body position has a smaller influence on the value of the reservoir quality. The quality of the single-well reservoir is directly determined by the drilling length of the high-quality reservoir, and the reservoir quality can be better reflected compared with the position of a target body.
And (4) calculating the completion quality of the ith well to be evaluated by adopting a formula (3).
Wherein, CLiValue of initial fracture uncrushed section length, CS, for the ith well to be evaluatediValue of primary fracture sand addition intensity, CW, for the ith well to be evaluatediIs the value of the primary fracturing fluid strength of the ith well to be evaluated.
Equation (3) is based on the dovetail mutation model. The dovetail mutation model can predict the system behavior of 3 variables. As can be seen from equation (3), the magnitude of the value of the initial fracture uncrushed section length has the greatest effect on the value of the completion quality, and the magnitude of the value of the initial fracturing fluid strength has the least effect on the value of the completion quality. This is because the initial frac virgin zone is a major reconstruction zone of the repeated frac, and the reconstruction can be used to recover the reserves, so the length of the initial frac virgin zone is important. Secondly, earlier researches show that compared with the strength of the primary fracturing fluid, the primary fracturing sand adding strength has stronger correlation with the yield of a gas well and has larger influence on the productivity of the gas well, so that the primary fracturing sand adding strength is arranged before the strength of the primary fracturing fluid in importance ranking.
And (4) calculating the production dynamics of the ith well to be evaluated by adopting a formula (4).
Wherein, PCiFor the value of the cumulative gas production of the ith well to be evaluated, PEiValue of EUR for the ith well to be evaluated, PPiFor the value of the current pressure level of the ith well to be evaluated, PGiThe value of the current production level of the well to be evaluated, which is the ith well to be evaluated.
The formula (4) is obtained based on the butterfly mutation model. The butterfly mutation model can predict the system behavior of 4 variables. It can be seen from formula (4) that the current values of the accumulated gas production, the EUR, the current pressure level and the current production level have smaller influence on the value of the production dynamics in turn, because the current accumulated gas production and the EUR represent the current and predicted final production degree respectively, the production dynamics can be reflected better, and the pressure level is an important reflection of the formation energy and can also reflect the production dynamics to a certain extent.
Step 203: and calculating the normalized value of the evaluation index of each well to be evaluated.
The reservoir quality normalization value of the ith well to be evaluated is obtained by calculation according to a formula (7), the well completion quality normalization value of the ith well to be evaluated is obtained by calculation according to a formula (8), and the production dynamic normalization value of the ith well to be evaluated is obtained by calculation according to a formula (9).
Wherein max (r) is the maximum value among the reservoir qualities of all the wells to be evaluated, min (r) is the minimum value among the reservoir qualities of all the wells to be evaluated, max (c) is the maximum value among the completion qualities of all the wells to be evaluated, min (c) is the minimum value among the completion qualities of all the wells to be evaluated, max (p) is the maximum value among the production dynamics of all the wells to be evaluated, and min (p) is the minimum value among the production dynamics of all the wells to be evaluated.
Step 204: and (3) calculating the repeated fracture evaluation value of each well to be evaluated according to the formula (1).
Step 204 may be the same as step 103 shown in fig. 1, and is not described herein again.
Fig. 3 illustrates another evaluation method for shale gas horizontal well repeated fracturing provided by the embodiment of the invention, and compared with the evaluation method illustrated in fig. 2, the evaluation method illustrated in fig. 3 will describe how to obtain the value of the dependent sub-indicator of each well to be evaluated. Referring to fig. 3, the method includes the following steps.
Step 301: and collecting the actual value of the subordinate sub-index of each well to be evaluated.
In particular, the actual values of the dependent sub-indices of reservoir quality are mainly obtained from the basic geological evaluation results. The basic geological evaluation result is specifically a reservoir classification evaluation result and a horizontal well logging interpretation result. The 'drilling length of the high-quality reservoir' can be directly obtained from reservoir classification evaluation results and horizontal well logging interpretation results. The "target position" is actually a range of formation thicknesses, and in shale gas horizontal well drilling, the optimal target position is typically designed to be a small layer or a few small layers, for example, the target position for a Changning shale gas field is designed to be 1+2 small layers. In order to quantitatively evaluate the position of the target body, the method can be characterized by the passing proportion of the horizontal section in the optimal target body, and the range of the passing proportion is 0-100%. The method comprises the steps of collecting the actual value of the target body position of each well to be evaluated, wherein the step of collecting the passing proportion of the horizontal section of the well to be evaluated in the optimal target body is used as the actual value of the target body position.
In particular, the actual values of the sub-indicators of dependency of the completion quality may be obtained from the basic parameters and the fracturing construction parameters of the shale gas horizontal well.
Specifically, the actual values of the dependent sub-indicators of the production dynamics mainly come from the daily production dynamic parameters of the shale gas horizontal well, wherein the current production level, the current pressure level and the current accumulated gas production can be directly read, and the EUR can be obtained through prediction on the basis of descending analysis.
Step 302: and preprocessing the acquired actual values of the subordinate sub-indexes to obtain the corrected values of the subordinate sub-indexes of each well to be evaluated.
Wherein, the correction value of each dependent sub-index is not less than 0 and not more than 1.
Since the units of the subordinate sub-indexes are different, the numerical values of the subordinate sub-indexes may have large difference in magnitude, and in order to avoid the possibility that the large number annihilates the small number when calculating the value of the evaluation index, the actual values of the subordinate sub-indexes must be processed, the subordinate sub-indexes are dimensionless, and the values of the subordinate sub-indexes are mapped into the range of [0, 1], so that the subordinate sub-indexes are guaranteed to be values between 0 and 1.
Preferably, the pretreatment mode comprises:
when min (x)ij) And max (x)ij) When the j sub-index is not equal and the j sub-index is the first sub-index, preprocessing the actual value of the j sub-index according to a formula (5); the first subordinate sub-index comprises a target body position, a high-quality reservoir drilling length, a primary fracturing unpressurized section length and a current pressure level.
When min (x)ij) And max (x)ij) And when the j-th dependent sub-index is not equal and is not the first dependent sub-index, preprocessing the actual value of the j-th dependent sub-index according to the formula (6).
When min (x)ij) And max (x)ij) And when the j-th sub-indexes are equal, setting the correction values of the j-th sub-indexes of all the wells to be evaluated to be 0.
Wherein x isijIs the actual value, y, of the j-th dependent sub-index of the ith well to be evaluatedijFor the ith well to be evaluatedCorrection value of jth dependent sub-index, max (x)ij) The maximum value of the actual values of the j-th subordinate sub-indexes of all the wells to be evaluated; min (x)ij) The minimum value of the actual values of the j-th dependent sub-index of all the wells to be evaluated.
Step 303: and calculating to obtain the value of the evaluation index of each well to be evaluated according to the corrected value of the subordinate sub-index of each well to be evaluated.
This step 303 may be the same as step 202 shown in fig. 2, and is not described herein again.
Step 304: and calculating the normalized value of the evaluation index of each well to be evaluated.
This step 303 may be the same as step 203 shown in fig. 2, or may be the same as step 102 shown in fig. 1, and is not described herein again.
Step 305: and (3) calculating the repeated fracture evaluation value of each well to be evaluated according to the formula (1).
This step 303 may be the same as step 204 shown in fig. 2, and is not described again here.
Step 306: and sequencing the wells to be evaluated according to the size sequence of the repeated fracture evaluation values.
Specifically, the wells to be evaluated may be ranked in order of the repeated fracture evaluation values from large to small.
Step 307: and selecting at least one well to be evaluated for repeated fracturing based on the sequence of the sequenced wells to be evaluated.
And the selected at least one well to be evaluated has a higher repeated fracture evaluation value than the non-selected well to be evaluated.
Specifically, when the order of the wells to be evaluated is arranged in the order of the repeated fracture evaluation values from large to small, the front well to be evaluated may be selected for repeated fracturing because the repeated fracture evaluation value of the front well to be evaluated is the highest and is more suitable for repeated fracturing.
The evaluation method for shale gas horizontal well repeated fracturing provided by the embodiment of the invention is described in detail below by taking the Changning shale gas field volume fractured horizontal well as an example and combining the evaluation methods shown in fig. 2 and fig. 3.
The Changning shale gas field is located in the southwest of Sichuan basin and spans the provinces of Changning county, Davidia county, Xingwen county and Yun Lian county, which are Yibin city of Sichuan province. The temperature of the regional inner layer is 87.02-110.60 ℃, the pressure coefficient is basically more than 1.20, and the whole body belongs to a normal-temperature overpressure gas reservoir; the produced fluid hydrocarbon is mainly methane (more than 98 percent on average), does not contain hydrogen sulfide and has low carbon dioxide content. And the shale gas horizontal wells in the region are subjected to volume fracturing modification and then flow back for production.
Taking the shale gas reservoir fracturing horizontal wells H1-H14 with 14 wells as an example, the evaluation process of repeated fracturing is explained.
Step 1): and collecting and sorting to obtain actual values of 9 subordinate sub-indexes including the drilling length of a high-quality reservoir, the position of a target body, the length of a primary fracturing non-fractured section, the primary fracturing sand adding strength, the strength of a primary fracturing liquid, the current accumulated gas yield, the EUR, the current pressure level and the current yield level. The actual values of the subordinate sub-indices of H1-H14 are shown in Table 1. It should be noted that, according to the development experience of the Changning shale gas field, the optimal target position is Longyi1 1One to one dragon1 2And the small layer, therefore, the index of '1 +2 small layer drilling encounter ratio' is used for quantitatively representing the quality of the target body position.
TABLE 1
Step 2): the dependent sub-indicators are pre-processed according to step 302 shown in fig. 3. The corrected values of the dependent sub-indices obtained after the pre-processing are shown in table 2.
TABLE 2
Step 3): and calculating the value of the evaluation index of each well to be evaluated according to the step 303 shown in fig. 3.
Step 4): and calculating to obtain a normalized value of the evaluation index of each well to be evaluated according to the step 203 shown in fig. 2.
Step 5): and calculating the repeated fracture evaluation value of each well to be evaluated according to the step 305 shown in fig. 3, and sequencing the wells to be evaluated according to the sequence of the repeated fracture evaluation values from large to small. Table 3 shows the replicate fracture estimates and sequence numbers for each well under evaluation.
TABLE 3
It will be understood by those skilled in the art that all or part of the steps for implementing the above embodiments may be implemented by hardware, or may be implemented by a program instructing relevant hardware, where the program may be stored in a computer-readable storage medium, and the above-mentioned storage medium may be a read-only memory, a magnetic disk or an optical disk, etc.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (5)
1. A method for evaluating repeated fracturing of a shale gas horizontal well, the method comprising:
acquiring actual values of subordinate sub-indexes of the evaluation indexes of each well to be evaluated; the well to be evaluated is a fractured shale gas horizontal well, and the evaluation indexes comprise reservoir quality, completion quality and production dynamics of the well to be evaluated; the subordinate sub-indexes of the reservoir quality comprise a target body position and a good-quality reservoir drilling length of a well to be evaluated, the subordinate sub-indexes of the well completion quality comprise a primary fracturing non-fractured section length, a primary fracturing sand adding strength and a primary fracturing fluid strength, and the subordinate sub-indexes of the production dynamics comprise a current accumulated gas production rate, a predicted final recoverable reserve, a current pressure level and a current yield level;
preprocessing the acquired actual values of the subordinate sub-indexes to obtain corrected values of the subordinate sub-indexes of each well to be evaluated; the correction value of each subordinate sub-index is not less than 0 and not more than 1;
calculating to obtain the value of the evaluation index of each well to be evaluated according to the determined correction value of the subordinate sub-index of each evaluation index;
calculating a normalized value of the evaluation index of each well to be evaluated;
calculating the repeated fracturing evaluation value of each well to be evaluated according to the following formula;
wherein, RFiA repeated fracture evaluation value R for the ith well to be evaluatediValue of reservoir quality for the ith well under evaluation, CiIs the value of the completion quality of the ith well to be evaluated, PiFor the value of the production dynamics of the ith well under evaluation,
and
are respectively the RiThe C isiAnd said PiI is an integer, i is more than or equal to 1 and less than or equal to n, 2 and less than or equal to n, and n represents the number of the wells to be evaluated;
the reservoir quality of the ith well to be evaluated is calculated by adopting the following formula:
wherein RLiFor the ith saidEvaluating a value for a premium reservoir run-length, RP, of a welliThe value of the target body position of the ith well to be evaluated;
the completion quality of the ith well to be evaluated is calculated by adopting the following formula:
wherein, CLiFor the value of the initial fracture uncrushed section length, CS, of the ith well to be evaluatediFor the value of the primary fracture sand addition intensity, CW, of the ith well to be evaluatediThe value of the strength of the primary fracturing fluid of the ith well to be evaluated;
the production dynamics of the ith well to be evaluated is calculated by adopting the following formula:
wherein, PCiFor the value of the current gas production accumulated for the ith well to be evaluated, PEiFor the predicted final recoverable reserve value, PP, for the ith said well under evaluationiFor the value of the current pressure level of the ith well to be evaluated, PGiThe value of the current production level of the well to be evaluated is the ith well to be evaluated.
2. The method according to claim 1, wherein the preprocessing of the actual values of the collected dependent sub-indicators comprises:
when min (x)ij) And max (x)ij) When the j (th) subordinate sub-index is not equal and is the first subordinate sub-index, the j (th) subordinate sub-index is the first subordinate sub-index according to a formula
Preprocessing the actual value of the jth subordinate sub-index; the first subordinate sub-index comprises the target body position, the premium reservoir drilling length and the placeThe primary fracture uncrushed section length and the current pressure level;
when min (x)ij) And max (x)ij) When the j (th) subordinate sub-index is not equal and the j (th) subordinate sub-index is not the first subordinate sub-index, according to a formula
Preprocessing the actual value of the jth subordinate sub-index;
when min (x)ij) And max (x)ij) When the j sub indexes are equal, setting the correction values of the j sub indexes of all the wells to be evaluated as 0;
wherein x isijThe actual value y of the j-th subordinate sub index of the ith well to be evaluatedijA corrected value, max (x), of the jth subordinate sub-index of the ith well to be evaluatedij) The maximum value of the j actual values of the subordinate sub indexes of all the wells to be evaluated; min (x)ij) The minimum value is the actual value of the jth subordinate sub-index of all the wells to be evaluated.
3. The method of claim 1, wherein collecting actual values of target body position for each of the wells under evaluation comprises:
and acquiring the passing proportion of the horizontal section of the well to be evaluated in the optimal target body as an actual value of the position of the target body.
4. The method of claim 1,
the normalized value of the reservoir quality of the ith well to be evaluated adopts a formula
The calculation results in that,
the normalized value of the completion quality of the ith well to be evaluated adopts a formula
The calculation results in that,
the normalized value of the production dynamics of the ith well to be evaluated adopts a formula
The calculation results in that,
wherein max (r) is the maximum value among the reservoir qualities of all the wells to be evaluated, min (r) is the minimum value among the reservoir qualities of all the wells to be evaluated, max (c) is the maximum value among the completion qualities of all the wells to be evaluated, min (c) is the minimum value among the completion qualities of all the wells to be evaluated, max (p) is the maximum value among the production dynamics of all the wells to be evaluated, and min (p) is the minimum value among the production dynamics of all the wells to be evaluated.
5. The method according to any one of claims 1 to 4, further comprising:
selecting at least one well to be evaluated for repeated fracturing; and the selected at least one repeated fracture evaluation value of the well to be evaluated is higher than the repeated fracture evaluation values of the unselected wells to be evaluated.
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| CN113266328A (en) * | 2020-02-17 | 2021-08-17 | 中国石油天然气股份有限公司 | Method and device for evaluating fracturing effect of shale reservoir |
| CN112228052B (en) * | 2020-10-30 | 2023-07-25 | 中国石油天然气股份有限公司 | Shale and tight rock oil gas productivity prediction method, evaluation method and system |
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