Same-layer synchronous fracturing method for local well and adjacent well

Abstract

The invention belongs to the technical field of petroleum geology development, and discloses a same-layer synchronous fracturing method for a local well and an adjacent well. Comprising the steps of establishing historical fracturing data, establishing a relation curve of the well depth and the pump stopping pressure of the same layer section, drawing a fitting graph of the relation curve of the pump stopping pressure and the pressure channeling of all fractured wells in an area, and establishing a half-fracture length relation curve template suitable for different well pattern and well spacing conditions based on different prepad fluid fracture forming conditions in the area. In the fracturing process, the risk of safety and environmental protection caused by east-west oil well channeling of the adjacent well can be effectively avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of petroleum geological development, and in particular relates to a method for judging the possibility of impending well breakout during vertical well fracturing in an extremely high water-cut development period and for performing synchronous interference fracturing in the same layer. Background Art

[0002] For the old Fuyu oilfield in the Songliao Basin, which has been developed by water injection for more than 60 years, water injection development has entered the period of extremely high water content development, and the distribution characteristics of residual oil have changed. It is currently present in the low permeability parts of the layer, between oil and water wells, and in the poor water drive position. As the distribution characteristics of the remaining oil have changed, the previous fracturing technology for old wells has become unsuitable, and the fracturing effect and benefits have stagnated. Therefore, in view of the current situation of poor fracturing effect, the research has tackled the fracturing technology of increasing the pre-fluid to create long cracks, the fracturing technology of increasing the displacement, the fracturing technology of variable displacement, and the temporary plugging fracturing technology. Although good results have been achieved, due to the dense well network and the characteristics of artificial fractures mainly in the east-west direction, there is a risk of oil wells running during the fracturing process, which is easy to cause safety and environmental risks. According to the analysis data of China's modern tectonic stress field, Northeast my country is mainly affected by the subduction of the Pacific Plate, with weak compressive shear stress as the main effect, and the main compressive stress direction is close to the east-west direction. The field monitoring data of hydraulic fracturing also proves this point. The direction of the fracture extension is along the direction of the maximum principal stress, that is, close to the east-west direction. Since the fracturing cracks in Fuyu Oilfield are mainly east-west cracks, and the distance between oil wells is between 80 meters and 150 meters, it is easy to cause east-west well channeling during fracturing. In addition, the remaining oil is distributed in the blind areas between oil wells and the areas not affected by water wells, so the fracturing effect of a single well is poor. Therefore, it is urgent to study a technical method that can avoid channeling and improve the fracturing effect under the same layer fracturing conditions. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides a method for synchronous fracturing of the well in the same layer. For oil reservoirs with artificially transformed fractures mainly in the east-west direction under dense well network conditions, in the process of well and layer selection, the planar distribution characteristics of the reservoir and the distribution characteristics of the same layer section on the plane, especially in the east-west direction, are analyzed.

[0004] The above object of the present invention is achieved through the following technical scheme: a method for fracturing the well in the same layer synchronously with the well adjacent to the well, the steps are:

[0005] S1. Establish historical fracturing data: Establish the construction parameters, pump stop pressure, and depth of all fracturing wells in the same layer in the geological unit to be inspected;

[0006] S2. Establishing a relationship curve between the well depth and the pump-off pressure in the same layer: Establishing a relationship curve between the well depth and the pump-off pressure in the same layer based on the historical fracturing data of step S1, and fitting the relevant parameters using the least squares method to obtain a relationship curve between the pump-off pressure and the well depth;

[0007] S3. Draw a fitting curve of the relationship between pump stop pressure and pressure channeling of all fracturing wells in the region based on the relationship curve obtained in step S2;

[0008] S4. Establishing a curve template for the relationship between the length of the semi-cracks under different well-pattern and well-spacing conditions based on different pre-fluid fracture conditions in the region: Using the relationship curve in step S2 and the fitting diagram in step S3, establishing a curve template for the length of the semi-cracks under different well-pattern and well-spacing conditions based on different pre-fluid fracture conditions in the region, firstly, establishing a geostress curve template under formation parameters based on the well logging data of the single well of the geological unit, establishing a data template based on the characteristics of the geostress curve combined with the data of the length, height, width and other data of the fracture under different displacements, analyzing and proposing the best construction parameters for preventing well channeling; for the layers where the remaining oil is located between wells and at the edge of the structure according to geological knowledge and the remaining potential between wells needs to be tapped, using the fracture morphology established in the region as a template, designing an appropriate amount of pre-fluid for the target layer according to the stress characteristics of the well pattern and the reservoir barrier layer, and designing the fracture penetration ratio to be 50-65%, so as to ensure that the fracture control area of ​​the single well is expanded to the middle area between the two wells and that no channeling can be achieved;

[0009] S5. Analyze the template created in step S4.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: during the fracturing process, east-west oil well channeling in adjacent wells can be effectively avoided to cause safety and environmental protection risks. On the other hand, by simultaneously fracturing the same layer section of the well and the adjacent well, channeling is prevented and the fracturing effect is improved; 5 groups of 8 wells are synchronously interfered with the well row. Compared with conventional repeated fracturing, the application of this fracturing technology increases the average daily fluid increase of a single well from 4.2t to 5.6t, and the daily oil increase from 0.3t to 0.45t. The effectiveness of the measure is increased to 92%. The water drive development effect of the fractured well area is good, and the water content increase rate is effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0012] Figure 1 It is a scatter plot of the relationship between the pump-off pressure of the geological unit and the pressure-channeling well;

[0013] Figure 2 It is a template diagram of the maximum and minimum principal stress relationship curve of the measured oil field block;

[0014] Figure 3 It is a simulation diagram of fracture morphology under different pre-fluid conditions of typical wells in the measured oil field block;

[0015] Figure 4 is the change diagram of fracture morphology under different pre-fluid conditions;

[0016] Figure 5 It is the interference cloud diagram of the middle position of the cracks when two wells are fracturing the same layer at the same time;

[0017] Figure 6 This is a schematic diagram of the number of fracturing and crack distribution of the five sub-layers in the measured oil field;

[0018] Figure 7 This is a schematic diagram of simultaneous interference fracturing in the same layer;

[0019] Figure 8 It is the well location map of the layer synchronous interference fracturing well;

[0020] Fig. 9 This is the synchronous fracturing construction curve of the same layer in Dongzhong+13-08.1 well and Dongzhong+13-08.1 well. DETAILED DESCRIPTION

[0021] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0022] Example 1

[0023] For oil reservoirs with artificially stimulated fractures mainly in the east-west direction under dense well network conditions, during the fracturing process, the fractures extend in the near east-west direction; secondly, under the influence of residual distribution characteristics under the conditions of ultra-high water-cut development period, the fracturing technology with the purpose of creating long fractures + multiple diversions to tap the potential of residual oil is prone to cause pressure channeling of nearby oil wells in the same row near the east and west, resulting in safety and environmental incidents in the nearby wells. At the same time, the post-fracturing effect of the well is deteriorated due to the channeling, and the residual oil cannot be effectively tapped. In view of the above problems, in the process of selecting wells and layers, the planar distribution characteristics of the reservoir and the distribution characteristics of the same layer section on the plane, especially in the east-west direction, are analyzed. Secondly, the distribution characteristics of the remaining oil are understood. For the east-west wells with the risk of channeling, the same layer section is adopted in terms of engineering technology. Two groups of fracturing vehicles are adopted. Synchronous construction is carried out on the basis of synchronization of displacement and fracturing construction parameters. The same layer, displacement, sand addition amount and sand addition speed are synchronized. In the process of fracture extension along the near east-west direction, interference may be generated. In the process of extension, fractures from different directions collide and resonate, and then a fracture network is generated, which can cause the fracture to turn and form new fractures, increase the range of fractures in the plane and vertical direction, and effectively improve the degree of reservoir utilization. At the same time, artificial fractures can extend vertically (equivalent to longitudinal waves). At the same time, the method of changing displacement at the same time is adopted during the construction process, which is conducive to the lateral extension of fractures (equivalent to transverse waves). Changing displacement is equivalent to applying forces of different frequencies to an object, and the molecules of the object move, which can generate vibration.

[0024] Under the conditions of dense well network and the geological requirements of the target formation for fracturing, a curve template and relationship between pump stop pressure and formation depth are established for all wells in the selected well block that have been fractured in this layer. Predictive manual intervention is carried out for wells whose pump stop pressure is lower than the average pump stop pressure in the area. When selecting geological wells, engineers propose to give priority to east-west wells adjacent to the wells for simultaneous interference to avoid pressure channeling. It can be clearly seen that the pump stop pressure of the wells with pressure channeling is lower than the pressure in the area during fracturing in this layer. Due to the well channeling during fracturing, a pressure relief channel is formed, resulting in rapid release of pressure after fracturing. The wellhead shows the characteristics of low pump stop pressure. The method and steps for judging pressure channeling caused by predictability, at the same time, for the wells that have been pressure channeled in the past or may be pressure channeled, a method for synchronous fracturing of adjacent wells in the same layer is invented.

[0025] Step 1: Establish historical fracturing data. Technical personnel establish the construction parameters, pump-off pressure (the most critical factor), and depth of all fracturing wells in the same layer in all different geological units (Table 1).

[0026] Step 2: Establish the relationship curve between the well depth and the pump-off pressure in the same layer section, and use the least squares method to fit the relevant parameters to obtain the relationship curve between the pump-off pressure and the well depth.

[0027] P=2.36+0.0063h+ρgh / 1000000......(1)(Different formulas in different blocks)

[0028] Step 3: Draw a curve fitting diagram of the relationship between pump stop pressure and pressure channeling for all fracturing wells in the area

[0029] Table 1 Relationship between the depth of fractured wells in XX geological units and the pump stop pressure of each well

[0030]

[0031] pass Figure 1 It can be clearly seen that the pump stop pressure of the pressure channeling wells in this area is below 2.6 MPa. Therefore, when selecting wells for fracturing again for this type of pressure channeling well geology, it is necessary to adopt the anti-pressure channeling synchronous interference fracturing technology. If the pump stop pressure is lower than or close to this value, it is very easy to cause pressure channeling after increasing the construction scale during the second fracturing. When formulating a plan, it is necessary to adopt the synchronous interference fracturing mode in the same layer of the adjacent wells of this well.

[0032] Step 4: The wells that did not undergo fracturing during the last pump-stopping fracturing cannot be used as the basis for determining whether the wells undergo fracturing during the second fracturing. A half-crack length relationship curve template suitable for different well patterns and well spacing conditions based on different forefill fluid fracture conditions in the region was invented.

[0033] Firstly, based on the single well logging data of geological units, a template of geostress curve under formation parameters was established. According to the characteristics of geostress curve and the data of fracture length, height, width and other data of fracture morphology under different displacement, a data template was established and analyzed to propose the optimal construction parameters for preventing well channeling ( Figure 2-Figure 5 ). For the geological knowledge that the remaining oil is located between wells and at the edge of the structure, it is necessary to tap the potential of the remaining layer between wells. The fracture morphology established in this area is used as a template. According to the stress characteristics of the well pattern and reservoir barrier, an appropriate amount of pre-fluid is designed for the target layer. The fracture penetration ratio is designed to be 50-65% to ensure that the single well fracture control area is expanded to the middle area between the two wells and that pressure channeling cannot be prevented.

[0034] Step 5: Through numerical simulation calculation, it is found that when the adjacent wells in the same layer are fracturing at the same time, the cracks interfere with each other during the extension process, forming complex cracks. On the one hand, the cracks in one well are prevented from extending in the east-west direction. On the other hand, the two main cracks interfere with each other during the extension process and prevent each other from extending. The cracks extend rapidly to the surroundings at the contact surface, forming complex cracks, thereby achieving the effect of multi-directional and multi-angle cracks. By adding proppants, the purpose of effectively supporting complex cracks can be achieved ( Figure 5 ).

[0035] The method includes: when designing, the penetration ratio is 50% of the distance between the two oil wells, and complex fractures can be formed while interfering. The design optimization parameters can be seen in Appendix 2. When designing, for the same layer, the same fracturing parameters are adopted, including pre-fluid volume, displacement, step length, sand adding speed, sand adding volume, and post-fluid volume. (Specific design intervals are shown in Table 2).

[0036] Table 2: Design parameters of synchronous fracturing in the same layer of Dongzhong+13-08.11 well and Dongzhong+13-08.1 well

[0037]

[0038] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for fracturing a well in the same layer and simultaneously with the well adjacent to the well. It is characterized in that The steps are: S1. Establish historical fracturing data; S2. Establish the relationship curve between the well depth and the pump stop pressure in the same layer section; S3. Draw a fitting curve of the relationship between pump stop pressure and pressure channeling of all fracturing wells in the region based on the relationship curve obtained in step S2; S4. Establish a half-fracture length relationship curve template suitable for different well patterns and spacing conditions under different pre-fluid fracture conditions in the region.

2. The method for fracturing the adjacent wells in the same layer synchronously according to claim 1, It is characterized in that The step S1 specifically includes: establishing the construction parameters, pump stop pressure, and depth of all the fracturing wells in the same layer in the geological unit to be inspected.

3. The method for fracturing the adjacent wells in the same layer synchronously according to claim 1, It is characterized in that The step S2 specifically includes: establishing a relationship curve between the well depth and the pump-off pressure in the same layer section according to the historical fracturing data of step S1, and fitting relevant parameters using the least square method to obtain a relationship curve between the pump-off pressure and the well depth.

4. The method for fracturing the adjacent wells in the same layer synchronously according to claim 1, It is characterized in that The step S4 is specifically as follows: using the relationship curve in step S2 and the fitting diagram in step S3 to establish a half-crack length relationship curve template suitable for different well patterns and well spacing conditions under different pre-fluid fracture conditions in the region, firstly based on the single well logging data of the geological unit, a ground stress curve template under the formation parameters is established, and according to the characteristics of the ground stress curve combined with the data of the length, height, width and other data of the fracture morphology under different displacements, a data template is established, and analysis is performed to propose the best construction parameters for preventing well channeling; for the layers where the remaining oil is located between wells and at the edge of the structure according to geological knowledge and the remaining potential between wells needs to be tapped, the fracture morphology established in the area is used as a template, and according to the stress characteristics of the well pattern and the reservoir barrier layer, an appropriate amount of pre-fluid is designed for the target layer, and the fracture penetration ratio is designed to be 50-65%, so as to ensure that the fracture control area of ​​the single well is expanded to the middle area between the two wells and that channeling is impossible.

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