Method for evaluating fracturing effect based on fracturing construction pressure and pump stopping pressure

Abstract

The invention discloses a method for evaluating a fracturing effect based on fracturing construction pressure and pump stopping pressure. The method comprises the following steps that S1, logging, fracturing and after-fracturing extraction data of a to-be-evaluated well are collected; s2, the perforation middle vertical depth of the target well section is extracted, and the fracturing construction pressure, the pump stopping pressure and the yield of the stable yield stage are counted; s3, calculating the bottom hole pressure P after the target well is processed; s4, calculating the bottom hole pressure gradient G after the target well is processed; s5, calculating the pump stopping pressure gradient G1 of the target well; s6, compiling and generating a pressure gradient ratio diagram according to the pressure gradient; s7, marking the well number and yield division of the corresponding target well on the pressure gradient ratio diagram.The method is suitable for the technical field of oil and gas reservoir development, the pressure data in fracturing construction are effectively compared, the ratio diagram is compiled, the fracturing effect and the relation between the pressure and the daily output are visually evaluated, and the method has the advantages of being high in practicability and easy to popularize. And the fracturing effect of the whole area can be reflected more effectively.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir development, and in particular is a method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure. Background Art

[0002] As an unconventional natural gas in coal seams, deep-seated coalbed methane is mainly composed of methane (CH4), which is mainly stored in coal seams in an adsorbed state. At present, the main production increase measure is fracturing. For coal seams with poor physical properties, fracturing must be used to achieve the purpose of production, so the evaluation of fracturing effect is particularly important.

[0003] At present, the main fracturing evaluation methods include fracturing diagram technology, complex microseismic measurement technology, and pressure analysis before or after fracturing. Fracturing diagram technology (such as tracers and electromagnetic measurements) can more intuitively display the backflow situation after fracturing and infer the development of fractures, but its disadvantages are also obvious, and it has certain periodicity and limitations; complex microseismic measurement has a limited observation range, expensive instruments, and high cost of use.

[0004] Compared with fracturing diagram technology and microseismic measurement technology, pressure analysis before or after fracturing is the main method for evaluating the effect of fracturing construction, and is widely used in the evaluation of fracturing effect in oil and gas fields. For example: before fracturing, simulation software is used to simulate the fracturing scale (such as Cater model, KGD two-dimensional fracture extension model, PKN model, etc.); after fracturing, the double logarithmic curve of net pressure and time and the G function curve are used to analyze the fracturing effect.

[0005] Existing evaluation methods are almost all based on the analysis of models and dynamic pressure to evaluate the overall fracturing effect, which often have certain restrictions and limitations and are often inconsistent with the actual fracturing effect. Summary of the invention

[0006] The purpose of the present invention is to overcome the defects of the prior art and provide a method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure.

[0007] To achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure comprises the following steps:

[0009] Step S1, collecting well logging, fracturing and post-fracturing drainage data of the well to be evaluated;

[0010] Step S2, extracting the vertical depth of the middle part of the perforation of the target well section, and calculating the fracturing operation pressure, pump stop pressure and the production in the stable production stage;

[0011] Step S3, calculating the bottom hole pressure P of the target well after treatment;

[0012] Step S4, calculating the bottom hole pressure gradient G of the target well after treatment;

[0013] Step S5, calculating the pump-off pressure gradient G1 of the target well;

[0014] Step S6, generating a pressure gradient ratio map according to the pressure gradient;

[0015] Step S7, marking the corresponding target well number and production classification on the pressure gradient ratio map.

[0016] Preferably, in step S1, according to the actual situation of the study area, the well deviation data table, fracturing operation parameters and daily gas production in the production stage of the well to be evaluated are collected.

[0017] Preferably, in step S2, the construction pressure is used to reflect the pressure level of the entire fracturing construction;

[0018] The pump-off pressure is the pressure at the first moment after the water hammer effect stabilizes.

[0019] The production in the stable production stage is the daily gas production of the target well with stable production for more than 3 months under the same drainage and production system.

[0020] Preferably, in step S3, the static pressure P2 of the liquid column and the friction P3 of the wellbore are calculated based on the data collected in step S1, and the bottom hole pressure P=P1+P2-P3.

[0021] Preferably, in step S3, the liquid column static pressure formula is: P2 = ρgh

[0022] Where P2 represents the pressure of the liquid, ρ represents the density of the liquid, g represents the acceleration due to gravity, and h represents the height of the liquid.

[0023] Preferably, in step S3, the wellbore friction formula is:

[0024]

[0025] Among them, P3 is the friction resistance of the clean water pipe string, A is a constant of 1.3866, D is the inner diameter of the pipe string, Q is the displacement, and L is the length of the pipe string.

[0026] Preferably, in step S4, the bottom hole pressure gradient G after the target well is processed is P / TVD1;

[0027] Among them, P is the bottom hole pressure after treatment, and TVD1 is the vertical depth of the middle of the perforation section.

[0028] Preferably, in step S5, the target well pump stop pressure gradient G1=(P4+P2) / TVD1;

[0029] Among them, P4 is the pump stop pressure, P2 is the static pressure of the liquid column, and TVD1 is the vertical depth in the middle of the perforation section.

[0030] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0031] In the present invention, by effectively comparing the pressure data in the fracturing construction and compiling a ratio diagram, a method for intuitively evaluating the fracturing effect and the relationship between pressure and daily production is achieved. After obtaining the pressure data of a large number of production wells in the region, the gradient ratio ratio diagram compiled can more effectively reflect the fracturing effect of the entire region. The method also improves the understanding of the production scale of the entire region, the parameter selection is intuitive and reliable, the operation is simple, and the overall fracturing effect evaluation in the block is enhanced. Only simple calculations are required, which greatly improves the effect evaluation speed of regional fracturing and the timely correction of the fracturing construction plan, and improves the convenience and objectivity of the fracturing effect evaluation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a flow chart of a method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure according to an embodiment of the present invention;

[0033] Figure 2 is a diagram showing the ratio of the pressure gradient after treatment to the pump-off pressure gradient according to an embodiment of the present invention;

[0034] Figure 3 A diagram showing the ratio of the pressure gradient after treatment of a vertical well (inclined well) and the pressure gradient when the pump is stopped according to an embodiment of the present invention;

[0035] Figure 4 1 is a diagram showing the pressure gradient of each section of a horizontal well after treatment and the ratio of the pump-off pressure gradient according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are described in detail below.

[0037] The "range" disclosed in the present invention is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 10 to 50 is listed for a specific parameter, it is understood that the range of 10 to 40 and 20 to 50 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In this application, unless otherwise specified, the range of values ​​"a to b" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the range of values ​​"0 to 5" means that all real numbers between "0 to 5" have been fully listed in this article, and "0 to 5" is only an abbreviation of these numerical combinations.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0040] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0041] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0042] Unless otherwise specified, the reaction is carried out at room temperature and pressure.

[0043] Unless otherwise specified, all parts or percentages are by weight.

[0044] In the present invention, all substances used are known substances and can be purchased or synthesized by known methods.

[0045] In the present invention, the devices or equipment used are all conventional devices or equipment known in the art and are commercially available.

[0046] The following is a further description of the specific implementation of the method for evaluating the fracturing effect based on the fracturing operation pressure and the pump-off pressure of the present invention in conjunction with the embodiments. The method for evaluating the fracturing effect based on the fracturing operation pressure and the pump-off pressure of the present invention is not limited to the description of the following embodiments.

[0047] The fracturing construction curve is formed by real-time data collection at the fracturing construction site. The construction pressure and pump-off pressure are important components of the fracturing construction curve, important parameters for guiding fracturing construction, and important indicators for evaluating the formation of formation fracture networks. The construction pressure and pump-off pressure have practical significance for evaluating the fracturing construction effect and the gas production after fracturing. In order to eliminate the influence of well depth on the pressure value, the pressure gradient method is selected for drawing, and a relationship diagram with gas production is established to evaluate the fracturing construction effect. Based on the evaluation of the fracturing effect by dynamic pressure changes, the present invention uses previous pressure data and current gas production to evaluate the gas production of producing wells and the fracturing effect, as well as predict the production of new wells.

[0048] like Figure 1 As shown, the method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure of the embodiment of the present invention comprises the following steps:

[0049] Step S1, collecting logging, fracturing and post-fracturing drainage data of the well to be evaluated.

[0050] According to the actual situation of the study area, the main collection is the well deviation data table, fracturing construction parameters and daily gas production in the production stage of the wells to be evaluated.

[0051] Step S2, extracting the vertical depth of the middle part of the perforation of the target well section, and calculating the fracturing operation pressure, pump stop pressure and production in the stable production stage.

[0052] Specifically, the construction pressure is the main evaluation parameter, and the present invention fully considers its accuracy and representativeness. The selected construction pressure can fully reflect the pressure level of the entire fracturing construction. When selecting the pump stop pressure, the present invention considers the influence of the water hammer effect caused by instantaneous pump stop, and selects the first time pressure after the water hammer effect stabilizes as the pump stop pressure; in order to more accurately and representatively calculate the daily gas production, the present invention selects the daily gas production of the target well with stable production for more than 3 months under the same drainage system.

[0053] Step S3, calculating the bottom hole pressure P of the target well after treatment.

[0054] Specifically, the bottom hole pressure of the target well after treatment is calculated using the formula P = P1 + P2 - P3, where P1 is the construction pressure (MPa), P2 is the static pressure of the liquid column (MPa), and P3 is the wellbore friction (MPa).

[0055] Based on the data collected in step 1, calculate the static pressure P2 of the liquid column and the wellbore friction P3.

[0056] Liquid column static pressure formula:

[0057] P2=ρgh(1);

[0058] Among them, P2 represents the pressure of the liquid, ρ represents the density of the liquid, g represents the acceleration of gravity, and h represents the height of the liquid;

[0059] Wellbore friction formula:

[0060]

[0061] Wherein, P3-friction resistance of clean water pipe MPa, A-constant 1.3866, D-inner diameter of pipe mm, Q-displacement m3 / min, L-length of pipe m.

[0062] It should be noted that the friction resistance of the fracturing fluid with added resistance reducing agent should also be subtracted from the resistance reducing pressure.

[0063] Step S4, calculating the bottom hole pressure gradient G of the target well after treatment, where:

[0064] G = P / TVD1 (3);

[0065] Wherein, P is the bottom hole pressure after treatment (MPa), TVD1 is the vertical depth of the middle of the perforation section (m), and the relevant vertical depth data can be queried in step S1.

[0066] Step S5, calculating the target well pump stop pressure gradient G1, where:

[0067] G1=(P4+P2) / TVD1(4);

[0068] Among them, P4 is the pump stop pressure (MPa), P2 is the static pressure of the liquid column (MPa), and TVD1 is the vertical depth in the middle of the perforation section (m). In step S1, relevant vertical depth data can be queried.

[0069] Step S6, generating a pressure gradient ratio map according to the pressure gradient;

[0070] Figure 2 The pressure gradient ratio diagram after treatment and the pump-off pressure gradient ratio diagram according to an embodiment of the present invention is a scatter plot, with the X-axis being the pump-off pressure gradient (MPa / 100m) and the Y-axis being the pressure gradient after treatment (MPa / 100m).

[0071] Production classification: Square (Class I well): gas production is greater than or equal to 2000m 3 / d; Triangle (Class II well): gas production is greater than or equal to 1000m 3 / d, less than 2000m 3 / d; Circular (Type III well): gas production is less than 1000m 3 / d.

[0072] from Figure 2 The following points can be seen:

[0073] 1. The slope is between A and B, mainly Class I and Class II wells (the slope varies slightly depending on the block);

[0074] 2. The slope is greater than slope A and the treatment pressure gradient is greater than 3.5MPa / 100m, which is mainly Class III wells; the slope is greater than slope A and the pump-off pressure gradient is 3.0-3.5MPa / 100m, which is mainly Class III wells;

[0075] 3. The smaller the processing pressure gradient and the pump stop pressure gradient, the higher the daily gas production.

[0076] Step S7, marking the corresponding target well number and production classification on the pressure gradient ratio map.

[0077] In order to distinguish the distribution characteristics of daily production wells intuitively and quickly, two slope lines A and B are drawn empirically according to different blocks to distinguish the distribution characteristics of daily production wells; the larger the slope A, the higher the construction pressure; the smaller the slope B, the lower the pump stop pressure, and the smaller the minimum resistive stress of the reaction formation.

[0078] The present invention uses the relationship between construction pressure and pump-off pressure to calculate the processed fracturing gradient and pump-off pressure gradient, and then compiles a gradient ratio diagram, and finally marks the relevant well numbers and daily production. The gradient ratio diagram can be used to more intuitively evaluate the fracturing effect and daily production of the entire area.

[0079] The following is a further detailed description in conjunction with the accompanying drawings and examples of the present invention, but the examples should not be used as a limitation of the present invention. Taking the deep coalbed methane in the Yushe-Wuxiang block of the Qinshui coalfield in Shanxi Province as an example, the following steps are included:

[0080] (1) Collect logging, fracturing and production data of several (theoretically the more the better) gas producing wells in the study area and proceed to step (2);

[0081] (2) Count the vertical depth (m) of the middle part of the perforation of the target layer, the fracturing operation pressure (MPa), and the pump stop pressure (MPa) (Table 1, Table 2), and proceed to step (3);

[0082] (3) Calculate P2 using the liquid column static pressure formula and P3 using the wellbore friction formula through fracturing related parameters, calculate the processed bottom hole pressure P according to the calculation formula in step (3), and proceed to step (4);

[0083] (4) Using the processed bottom hole pressure P and the vertical depth data of the middle part of the perforation in step (2), the processed bottom hole pressure gradient G is calculated by the calculation formula in step (4), and then proceeding to step (5);

[0084] (5) Using the pump-off pressure P in step (2), the vertical depth data of the middle part of the perforation in step (2), and the static pressure P2 of the liquid column calculated in step (3), the pump-off pressure gradient G1 is calculated by the calculation formula in step (5), and the process proceeds to step (6);

[0085] (6) Calculate and compile a pressure gradient ratio diagram based on the pressure gradient ( Figure 2 , Figure 3 ), go to step (7);

[0086] (7) Mark the corresponding target well number on the pressure gradient ratio map.

[0087] (8) Figure 3 Table 1 is the evaluation and verification of the fracturing effect of vertical wells (inclined wells). Table 1 is the relevant processing data and daily gas production statistics of vertical wells (inclined wells).

[0088]

[0089] Table 1 (vertical well / inclined well)

[0090] Figure 3 The figure is the ratio of the pressure gradient after treatment and the pressure gradient when the pump is stopped. The X axis is the pressure gradient when the pump is stopped, and the Y axis is the pressure gradient after treatment. Square (Class I well): gas production is greater than or equal to 2000m 3 / d; Triangle (Class II well): gas production is greater than or equal to 1000m 3 / d, less than 2000m 3 / d; Circular (Type III well): gas production is less than 1000m 3 / d; Diamond (new fracturing): no gas wells found. The dotted lines are slope lines with slopes of 1.14 and 0.9 respectively.

[0091] 1. From Figure 3 It can be found that the new wells such as ZJ-21, ZJ-23 and ZJ-26 are all in the slope range of 0.9-1.14. A preliminary evaluation was conducted based on the on-site casing pressure and liquid production, which is basically consistent.

[0092] 2. From Figure 3It can be seen that Well ZJ-24, Well ZJ-27 and Well ZJ-29 are outside the slope. A preliminary evaluation was conducted based on the on-site casing pressure and liquid production. It was found that parameters such as liquid production were significantly lower than those of other wells. Based on this, a more detailed comprehensive re-evaluation of the geological conditions, fracturing scale, perforation method, etc. of the well can be carried out to optimize the fracturing process.

[0093] (9) Figure 4 Table 2 Evaluation and verification of horizontal well fracturing effect. Table 2 is the relevant processing data and daily gas production statistics of horizontal wells.

[0094]

[0095] Figure 4 The pressure gradient of each section of the horizontal well after treatment and the pressure gradient when the pump is stopped are compared; the X-axis is the pressure gradient when the pump is stopped, and the Y-axis is the pressure gradient after treatment. The square and diamond are in the producing well, with a daily gas production of 14000m 3 / d and 20000m 3 / d high-yield well; the three red dotted lines are: 1. Slope 1.8 line; 2. Slope 0.8 line; 3. Processing pressure gradient 3.5MPa / 100m line.

[0096] from Figure 4 The gradient ratios of each section of the medium horizontal well are mainly in the triangular area formed by the three dotted lines. The first and second sections of the SP1-H1 well, the first section of the SP2-H3 well, and the third section of the SP3-H1 well are outside the triangular area. Through research, it is found that the perforation positions of the first section of the SP1-H1 well and the first section of the SP2-H3 well are both in the mudstone layer, which is difficult to construct. The comprehensive evaluation shows that the gas production contribution rate of these two sections is not high; the selection of perforation positions of the second section of the SP1-H1 well and the third section of the SP3-H1 well needs to be optimized.

[0097] The method for evaluating the fracturing effect based on the fracturing construction pressure and the pump-off pressure proposed in the present invention is a method for intuitively evaluating the fracturing effect and the production distribution by simply processing the fracturing and drainage data of the production wells in the block and compiling the corresponding pressure gradient ratio diagram. The present invention can make a quick evaluation of the fracturing effect in a relatively simple and direct manner; make a simple prediction of the gas production after fracturing; and timely correct the fracturing construction parameters to optimize the process.

[0098] The method for understanding the fracturing effect based on the relationship between the construction pressure and the pump stop pressure provided by the embodiment of the present invention has the following effects:

[0099] (1) The present invention is a method for intuitively evaluating the fracturing effect and the relationship between pressure and daily production by effectively comparing the pressure data during fracturing construction and compiling a ratio diagram. After obtaining the pressure data of a large number of production wells in the region, the gradient ratio ratio diagram compiled can more effectively reflect the fracturing effect of the entire region. The method also improves the understanding of the production scale of the entire region.

[0100] (2) The parameter selection of the present invention is intuitive and reliable, and the operation is simple. It enhances the overall fracturing effect evaluation in the block. Only simple calculations are required, which greatly improves the speed of regional fracturing effect evaluation and timely correction of fracturing construction plans, and improves the convenience and objectivity of fracturing effect evaluation.

[0101] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the protection scope of the present invention.

Claims

1. A method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure, characterized in that: The following steps are involved: Step S1, collecting logging, fracturing and post-fracturing drainage data of the well to be evaluated; Step S2, extracting the vertical depth of the middle part of the perforation of the target well section, and calculating the fracturing operation pressure, pump stop pressure and production in the stable production stage; Step S3, calculating the bottom hole pressure P of the target well after treatment; Step S4, calculating the bottom hole pressure gradient G of the target well after treatment; Step S5, calculating the pump-off pressure gradient G1 of the target well; Step S6, generating a pressure gradient ratio map according to the pressure gradient; Step S7, marking the corresponding target well number and production classification on the pressure gradient ratio map.

2. A method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure as claimed in claim 1, characterized in that: In the step S1, according to the actual situation of the study area, the well deviation data table, fracturing operation parameters and daily gas production in the production stage of the well to be evaluated are collected.

3. The method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure according to claim 1, characterized in that: In the step S2, the construction pressure is used to reflect the pressure level of the entire fracturing construction; The pump-off pressure is the pressure at the first moment after the water hammer effect stabilizes. The production in the stable production stage is the daily gas production of the target well with stable production for more than 3 months under the same drainage and production system.

4. The method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure according to claim 1, characterized in that: In step S3, the static pressure P2 of the liquid column and the friction P3 of the wellbore are calculated based on the data collected in step S1, and the bottom hole pressure P=P1+P2-P3.

5. A method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure as claimed in claim 4, characterized in that: In step S3, the liquid column static pressure formula is: P2 = ρgh Where P2 represents the pressure of the liquid, ρ represents the density of the liquid, g represents the acceleration due to gravity, and h represents the height of the liquid.

6. A method for evaluating fracturing effect based on fracturing construction pressure and pump stop pressure as claimed in claim 4, characterized in that: In step S3, the wellbore friction formula is: Among them, P3 is the friction resistance of the clean water pipe string, A is a constant of 1.3866, D is the inner diameter of the pipe string, Q is the displacement, and L is the length of the pipe string.

7. The method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure according to claim 1, characterized in that: In the step S4, the bottom hole pressure gradient G after the target well is processed is P / TVD1; Among them, P is the bottom hole pressure after treatment, and TVD1 is the vertical depth of the middle of the perforation section.

8. The method for evaluating the fracturing effect based on the fracturing construction pressure and the pump stop pressure according to claim 1, characterized in that: In step S5, the target well pump stop pressure gradient G1 = (P4 + P2) / TVD1; Among them, P4 is the pump stop pressure, P2 is the static pressure of the liquid column, and TVD1 is the vertical depth in the middle of the perforation section.

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