Method for determining optimal fracturing displacement based on control of multiple interlayers

Abstract

The invention relates to a method for determining optimal fracturing displacement based on control of multiple interlayers, and belongs to the technical field of petroleum fracturing. The method specifically comprises the following steps: understanding an electrical logging curve of a fractured target layer to obtain the reservoir permeability of each opening layer under the control of an interlayer; knowing the number of interlayer layers of a target layer; the most reasonable displacement of a fracturing target layer is determined through a dynamic method; and the net pressure calculation method verifies the optimal displacement determined by the stepped lift displacement. Compared with the prior art, the permeability of a plurality of oil-containing parts under the control of interlayers is known and analyzed, so that similar permeability layers are classified and divided, the optimal displacement is optimized according to the change trend of net pressure, the problem of insufficient transformation under the condition of multi-interlayer distribution characteristics caused by low displacement in the prior art is avoided, and the yield is increased.

Description

Technical Field

[0001] The present invention relates to a method for determining the optimal displacement in fracturing under the control of multiple interlayers, belonging to the technical field of oil fracturing. Background Art

[0002] In the oil field, fracturing is an important means of reforming oil reservoirs in oil development. Fracturing artificially creates fractures in the formation to improve the underground flow environment of oil, increase the production of oil wells, and play an important role in improving the bottom-hole flow conditions of oil wells, reducing interlayer interference, and improving the utilization of oil reservoirs. The net pressure in the fracture of an oil and gas well is the driving force for the extension of the fracturing fracture, and is directly related to the fracture volume formed by fracturing, the complexity of the fracture, the filtration of the fracturing fluid, the possibility of sand plugging, etc. It is a crucial parameter affecting fracturing construction. Therefore, the analysis of the net pressure in the fracturing fracture is a very important analysis method in the fracturing process. The net pressure in the fracture can reflect the formation conditions during the fracturing construction for real-time adjustment of construction measures, and can also be used to evaluate the construction effect after the fracturing construction.

[0003] For the selected fracturing interval in geology, what displacement can fracture multiple interlayers and fully exploit the remaining oil in the low-permeability and low-water-cut parts under the control of interlayers. Currently, the general determination methods are numerical simulation methods or empirical value methods. For old oil fields that have been developed for many years, especially high-water-cut oil fields with a water cut above 90%, these methods have large errors and a low coincidence rate with the actual situation on site, resulting in an unclear effect when re-fracturing or multi-fracturing the target layer of old wells during the ultra-high water cut development period. Regarding the distribution characteristics of the remaining oil under the control of multiple interlayers, the remaining oil is mainly concentrated in the low-permeability parts. Data statistics and test data show that under the control of multiple interlayers in the same fracturing interval, most of the fracturing support fractures will extend and be supported along the parts with high permeability and good physical properties. Affected by multiple factors such as formation closure pressure and proppant performance, the production will show a decreasing trend after fracturing. As time goes by, the production will drop significantly to the low point of profitable production. At this time, the layer is generally refractured. The previous practice was to increase the sand addition per meter by 5%-15% on the basis of the first fracturing under the same displacement for such reservoirs, and keep the displacement unchanged. This will only cause the original fracture to be re-fractured and extended, but the low-permeability and low-water-cut parts affected by the interlayers still cannot be effectively utilized, resulting in a poor effect. The current general practice is to increase the net formation pressure by injecting high-pressure temporary plugging agents while keeping the displacement unchanged. However, it can be found from the actual construction curves on site that, such as Figure 1As shown, after injecting the high-pressure temporary plugging agent, at the same displacement, the construction pressure generally rises by 0.5 - 2 MPa, the net pressure increases, and new parts are mobilized vertically. After 2 - 3 minutes, the pressure returns to the previous level, no new net pressure is generated, and the new parts are not effectively mobilized and supported. Therefore, for the second or more fracturing operations, adopting the above two methods does not yield satisfactory results.

[0004] There is an urgent need to develop a method for conducting secondary or multiple fracturing in old wells and optimizing the displacement to effectively mobilize the low-permeability and low-water-cut parts affected by multiple interbeds vertically. Summary of the Invention

[0005] Aiming at the problems of insufficient mobilization of remaining oil at low displacement during fracturing under the control of interbeds and how to determine the optimal displacement for fracturing under the control of multiple interbeds, the present invention provides a method for determining the optimal displacement for fracturing under the control of multiple interbeds. Before the fracturing construction, the net pressure values at different displacements are dynamically calculated by applying a stepwise increasing displacement to the fracturing interval, and at the same time, the curve of the net pressure change value at different displacements is plotted. The best displacement is selected through the trend of the net pressure change, avoiding the problem of insufficient transformation under the condition of multi-interbed distribution characteristics at low displacement in the past and increasing the production.

[0006] The technical solution adopted by the present invention is a method for determining the optimal displacement for fracturing under the control of multiple interbeds, specifically as follows:

[0007] Step 1: Understand the electric logging curves of the fracturing target layer to obtain the reservoir permeability of each open layer under the control of interbeds.

[0008] Step 2: Identify the number of interbeds in the target layer and classify them according to the reservoir permeability in Step 1.

[0009] Step 3: Determine the most reasonable displacement of the fracturing target layer by the dynamic method.

[0010] Step 4: Verify the optimal displacement determined by the stepwise increasing displacement by the net pressure calculation method.

[0011] Further, the reservoir permeability classification criteria in Step 1 are as follows: for the first-class open layer, the permeability is greater than 120 md; for the second-class open layer: 100 - 120 md; for the third-class open layer: 80 - 100 md; for the fourth-class open layer: 60 - 80 md; for the fifth-class open layer: 40 - 60 md; for the sixth-class open layer: 20 - 40 md; for the seventh-class open layer: 5 - 20 md; for the eighth-class open layer: 0.1 - 5 md.

[0012] Further, in Step 2, the interbeds are divided into interlayer interbeds and intra-layer interbeds, where the interlayer interbeds are the interbeds between layers; the intra-layer interbeds are the interbeds between single sand bodies within the layer.

[0013] Further, Step 3 specifically includes determining the minimum displacement, interval displacement, and maximum displacement. Before the formal fracturing, the fracturing equipment is used to construct in a manner of stepwise increasing displacement.

[0014] Further, the construction in the manner of stepwise increasing displacement using the fracturing equipment in Step 3 specifically means starting from the minimum displacement of the previous fracturing, determining the number of levels of stepwise increasing displacement, and gradually increasing the displacement to the maximum displacement, where the maximum displacement is the displacement when the increase amplitude of the pump shutdown pressure is the smallest, or there is no change, or it decreases.

[0015] Further, the interval displacement in Step 3 is incremented at an interval with an increment value of 2m 3 / min.

[0016] Further, the number of levels of stepwise increasing displacement in Step 3 is based on the maximum value among the permeability division standard and the number of interbeds.

[0017] Further, Step 4 specifically includes continuously monitoring the pump shutdown pressure after the pump is shut down, calculating the net pressure corresponding to each displacement, obtaining the change in the net pressure after fracturing this layer. When the net pressure between adjacent displacements does not increase or the increase amplitude is the smallest, the displacement corresponding to the weighted average is the optimal displacement, where the net pressure = pump shutdown pressure + static liquid column pressure - bottom hole closure pressure.

[0018] The present invention discloses a method for determining the optimal displacement in fracturing under the control of multiple interbeds. The beneficial effect is that compared with the prior art, the present invention recognizes and analyzes the permeabilities of multiple oil-bearing parts under the control of interbeds, thereby classifying and dividing similar permeability layers, and optimizing the best displacement through the change trend of the net pressure, avoiding the problem of insufficient transformation under the condition of multi-interbed distribution characteristics at low displacements in the past, and increasing the production. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following-described drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It shows a schematic diagram of the fracturing construction curve of XX layer in XX well;

[0021] Figure 2 It shows a schematic diagram of the relationship curve between the permeability of different reservoirs and the compressive strength;

[0022] Figure 3 It shows a schematic diagram of the curve of the net pressure changing with the displacement in Embodiment 1.

[0023] Specific implementation method

[0024] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part rather than all of the embodiments of the present invention. The description of at least one exemplary embodiment below is actually only illustrative and in no way restricts the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0025] To further understand the content of the present invention, the following further elaborates on this technical solution in combination with specific implementation manners.

[0026] Embodiment 1:

[0027] This embodiment provides a method for determining the optimal displacement during fracturing based on the control of multiple interbeds, specifically as follows:

[0028] Step 1: Understand the electric logging curves of the fracturing target layer to obtain the reservoir permeability of each opened layer under the control of interbeds. Through research, it is found that, as Figure 2 shown, within the same large interval, the layers with higher permeability are preferentially opened as the first-opened layers, and the layers with lower or much lower permeability are opened weakly or not opened. In the figure, the X-axis represents permeability and the Y-axis represents compressive strength. Under the condition of a pressure of 10 MPa, y = 75.443x -0.1467 , the correlation coefficient R 2 = 0.8318; under the condition of a pressure of 5 MPa, y = 57.717x -0.165 , the correlation coefficient R 2 = 0.8564; as Figure 2 shown, within the same interval, the fracturing layers are affected by interbeds and have different permeabilities. During fracturing, at the same displacement, the high-permeability layers are opened first, while the low-permeability layers are not opened. Then, it is necessary to increase the displacement to open the low-permeability layers. The reservoir permeability classification standard is as follows: for the first-class opened layers, the permeability is greater than 120 md; for the second-class opened layers: 100 - 120 md; for the third-class opened layers: 80 - 100 md; for the fourth-class opened layers: 60 - 80 md; for the fifth-class opened layers: 40 - 60 md; for the sixth-class opened layers: 20 - 40 md; for the seventh-class opened layers: 5 - 20 md; for the eighth-class opened layers: 0.1 - 5 md.

[0029] Step 2: Understanding the number of interlayers in the target layer, classifying according to the reservoir permeability in Step 1; the interlayers are divided into interlayer barriers and intra-layer interlayers. Among them, the interlayer barrier is the barrier between layers; the intra-layer interlayer is the interlayer between single sand bodies within the layer, with a thickness > 0.4m, and it is a shale or calcareous interlayer. The fracturing target layer is divided according to the reservoir permeability standard in Step 1. Under the control of interlayers, the permeability of each small reservoir is statistically analyzed, and the permeability levels within the same range are classified into one category.

[0030] Step 3: Generally, when designing fracturing parameters, the most important thing is to design the displacement. Generally, it is determined by software simulation based on the characteristics of the reservoir, the stress difference between reservoir interlayers, the thickness of the target layer, the well pattern characteristics, etc. For the development of old oilfields, the coincidence with the actual situation on site is relatively low, which is caused by the superposition of factors such as the long development time of old oilfields, the large number of fracturing operations on the target layer, and water injection interference. Therefore, the dynamic method is used to determine the most reasonable displacement of the fracturing target layer; specifically, the minimum displacement, interval displacement, and maximum displacement are determined. Before formal fracturing, the fracturing equipment is used to construct in a way of stepwise increasing displacement. Specifically, starting from the minimum displacement of the previous fracturing, the number of stepwise increasing displacement levels is determined, and the displacement is gradually increased to the maximum displacement. Among them, the maximum displacement is the displacement when the increase in the pump stop pressure is relatively low or there is no change or a decrease. The number of stepwise increasing displacement levels is based on the maximum value of the permeability classification standard and the number of interlayers. For example, if there are 3 interlayers and they are divided into two categories in total, then the number of stepwise increasing displacement levels is defined as 3 times. The interval of stepwise increasing displacement is generally 2m 3 / min as the increment. For example, the first fracturing starts at 2m 3 / min, with an interval of 2m 3 / min to design the stepwise increasing displacement construction plan before formal fracturing, as shown in Table 1.

[0031] Table 1 Dynamic fracturing construction displacement design

[0032]

[0033] Starting from the lowest displacement, after each construction for 2 - 5 minutes (specifically determined according to the on-site construction conditions), stop the pump and continuously monitor the pressure for 2 minutes to record the pressure change value after stopping the pump. And so on, until the increase in the pump-stopping pressure corresponding to the last two recorded displacements is relatively low or does not change or decreases. Record the values well. The weighted average of the last two recorded displacements is the maximum displacement during the formal fracturing construction. During the process of increasing the displacement, generally, the pump-stopping pressure also rises. However, if there is cross-layer fracturing or it exceeds the thickness of the current target layer, the pressure will no longer rise. Instead, when increasing the displacement, the pressure does not rise, or rises slowly or decreases. That is to say, there is cross-layer fracturing of the target layer or damage to the casing. When the displacement is greater than a certain value, increasing the displacement results in a relatively small increase in the net pressure, indicating that increasing the displacement has little effect on the net pressure. Increasing the displacement requires increasing the water horsepower and increasing the construction cost. In addition, from Table 2 showing the pressure change values under the stepped increase in displacement on-site, it can be seen that as the displacement increases, the pump-stopping pressure increases. After the increase, it indicates that a new layer or new part has been opened, the interlayer has been fractured, and the low-permeability part has been effectively supported. When increasing the displacement, if the pump-stopping pressure does not increase, it indicates cross-layer fracturing of the target layer and a higher net pressure cannot be established. Therefore, the maximum displacement is designed as the weighted average of the two displacements corresponding to the point where the increase in the pump-stopping pressure is relatively slow; it should be noted that the interval displacement is determined according to the actual situation.

[0034] Table 2 Pump-stopping pressures corresponding to different displacements under the stepped increase in displacement

[0035]

[0036] Step 4, verify the optimal displacement determined by the stepped increase in displacement using the net pressure calculation method. Specifically, continuously monitor the pump-stopping pressure after stopping the pump, and calculate the net pressure corresponding to each displacement. As shown in Table 3, obtain the change in the net pressure after fracturing this layer. When the net pressure between adjacent displacements does not rise or the rise amplitude is the smallest, the corresponding displacement is the optimal displacement, where the net pressure = pump-stopping pressure + static liquid column pressure - bottom-hole closure pressure. It can be seen from Table 3 that when the displacement is 4 m 3 / min, the calculated net pressure is 0.31 Mpa. Compared with the displacement of 2 m 3 / min, the pressure rises by 0.12 Mpa. When comparing 6 m 3 / min with 4 m 3 / min, the pressure rise amplitude is 0.1 Mpa. However, when the displacement rises to 8 m 3 / min, the net pressure only rises by 0.01 Mpa. The increase in displacement does not play a key role in the increase in the net pressure. When the net pressure does not rise or the rise amplitude is relatively small, the transformation of the target layer corresponding to this displacement has nearly reached the maximum. Therefore, the displacement determined according to the pump-stopping pressure is correct. As Figure 2 shown, it can be seen from the pump-stopping pressure that the displacement is 6 - 8 m 3Under the condition of / min, the increase in the pump shutdown pressure is very small. Therefore, it can be seen that the optimal displacement of this interval is (6 + 8) / 2 = 7 m 3 / min.

[0037] Table 3 Net pressure corresponding to different displacements at stepped increasing displacements

[0038]

[0039] The dynamic method is used to determine the optimal displacement according to different reservoir permeabilities and the number of interbeds and interlayers, so as to mobilize the parts to be mobilized required under the optimal displacement. Since 2022, this method has been applied internally in an oilfield to optimize the design displacement of 54 wells for testing. The average daily oil increase per well is 0.42 t, and the water cut has decreased by 3 percentage points. Among them, 24 wells were fractured in 2023, with an effective rate of 92%. The initial daily oil increase per well is 0.34 t. After implementation, the water cut has decreased significantly, the low-water-cut parts have been activated, the production of the first-line wells is stable, the liquid production and oil production have increased, and the water cut is stable; it has no impact on the injection wells and adjacent wells in the injection well group, and the production of the well group is stable.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for determining the optimal displacement in hydraulic fracturing based on the control of multiple interbeds, characterized in that, Specifically: Step 1: Understand the electric logging curves of the fracturing target layer to obtain the reservoir permeability of each open layer under the control of interbeds and interlayers; Step 2: Identify the number of interbeds and interlayers in the target layer and classify them according to the reservoir permeability in Step 1; Step 3: Determine the most reasonable displacement of the fracturing target layer by the dynamic method; Step 4: Verify the optimal displacement determined by the stepped-up displacement using the net pressure calculation method.

2. The method for determining the optimal displacement during hydraulic fracturing based on multiple interlayers according to claim 1, wherein The reservoir permeability classification criteria in Step 1 are as follows: for Class I open layers, the permeability is greater than 120 md; for Class II open layers: 100 - 120 md; for Class III open layers: 80 - 100 md; for Class IV open layers: 60 - 80 md; for Class V open layers: 40 - 60 md; for Class VI open layers: 20 - 40 md; for Class VII open layers: 5 - 20 md; for Class VIII open layers: 0.1 - 5 md.

3. The method for determining the optimal displacement in hydraulic fracturing based on the control of multiple interlayers according to claim 2, wherein In Step 2, the interbeds and interlayers are divided into interlayer interbeds and intra-layer interbeds. Among them, the interlayer interbeds are the interbeds between layers; the intra-layer interbeds are the interbeds between single sand bodies within the layer.

4. The method for determining the optimal displacement in hydraulic fracturing based on multiple interlayers according to claim 3, wherein Step 3 specifically involves determining the minimum displacement, interval displacement, and maximum displacement. Before formal fracturing, the fracturing equipment is used to construct in the way of stepped-up displacement.

5. A method for determining the optimal displacement in hydraulic fracturing based on the control of multiple interlayers as claimed in claim 4, wherein, In Step 3, the construction of stepped-up displacement using the fracturing equipment specifically starts from the minimum displacement of the previous fracturing as the starting point, determines the number of stepped-up displacement levels, and gradually increases the displacement to the maximum displacement. The maximum displacement is the displacement when the increase in the pump shut-off pressure is the lowest, or there is no change, or it decreases.

6. A method for determining the optimal displacement in hydraulic fracturing based on the control of multiple interlayers as claimed in claim 5, wherein In Step 3, the number of stepped-up displacement levels is based on the maximum value in the permeability classification criteria and the number of interbeds and interlayers.

7. A method for determining the optimal displacement in hydraulic fracturing based on the control of multiple interlayers according to claim 6, characterized in that In step 3, the intermittent displacement increases incrementally at an increment of 2 m 3 / min.

8. A method for determining the optimal displacement in fracturing based on the control of multiple interlayers according to claim 7, characterized in that, Step 4 specifically involves continuously monitoring the pump shut-off pressure after the pump is stopped, calculating the net pressure corresponding to each displacement, obtaining the change in the net pressure after fracturing of this layer. When the net pressure between adjacent displacements does not increase or the increase is the smallest, the displacement corresponding to the weighted average is the optimal displacement. Among them, the net pressure = pump shut-off pressure + static liquid column pressure - bottom hole closure pressure.

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