Reconstruction fracturing transformation method for dynamic chemical temporary plugging shaft of old well

Abstract

The invention discloses an old well dynamic chemical temporary plugging shaft reconstruction fracturing transformation method which comprises the following steps: analyzing a fractured exploitation block, and screening old wells meeting multi-gas commingling exploitation conditions; a degradable temporary plugging material is used for dynamic chemical plugging, and shaft reconstruction is achieved; after the upper fractured layer section is smoothly plugged, fracturing transformation is conducted on the lower reservoir; and degrading the temporary plugging material of the plugged layer section, recovering the gas production of the production layer, and discharging and mining together with the lower production layer. According to the method, the existing low-yield and low-efficiency well and old wellbay can be fully utilized to develop a new layer while efficient utilization of coal-series gas resources is assisted, and a new scientific strategic decision basis is provided for multi-gas collaborative development.

Description

Technical Field

[0001] The invention relates to the field of production enhancement and transformation of multi-lithology superimposed coal-measure gas reservoirs, and in particular to a method for dynamic chemical temporary plugging of wellbore and reconstruction and fracturing of old wells. Background Art

[0002] Coal-measure gas belongs to unconventional gas reservoirs and is an important development direction for increasing reserves and production of natural gas resources in my country. It refers to various natural gases stored in coal-bearing strata, including coalbed methane, tight sandstone gas, coal-measure shale gas and natural gas hydrates from coal-type gas sources. It is an efficient and clean energy source. Among them, coalbed methane, tight sandstone gas and coal-measure shale gas are usually referred to as "three coal-measure gases" or "coal-measure unconventional natural gas", which have the characteristics of "co-existence and multi-layer coexistence". Coal-measure gas superimposed reservoirs refer to multiple coal-measure gas symbiotic reservoirs that are continuously accumulated in the strata. With the continuous deepening of exploration and development, the production time of gas fields has increased, and the number of exhausted wells and low-yield and low-efficiency wells has increased year by year. For such unconventional natural gas reservoirs with a high degree of vertical multi-gas-containing systems superimposed on each other, new gas-containing systems can be opened in the old wellbore to contribute synergistically with the original production layer to achieve the improvement of the production capacity of the old wells.

[0003] Taking the Ordos Basin as an example, coalbed methane, tight sandstone gas and shale gas reservoirs are characterized by superposition vertically. Based on the principle of exhaustion of the previously mined layer and connection of the new gas-bearing system, chemical temporary plugging technology is used to temporarily seal the upper sandstone / shale / coal rock producing layers of the mined old wells, and wellbore reconstruction is implemented. Subsequently, a large-volume pressure is applied to open the lower new layer for three-dimensional comprehensive development. This can make full use of existing low-yield and inefficient wells and old well platforms, realize coordinated exploitation of multiple gases, effectively save exploration costs, increase the output and economic benefits of single wells, and provide a new idea for activating the production capacity of old wells.

[0004] The existing wellbore reconstruction technology mainly adopts mechanical plugging methods, such as casing patching technology, tubing + packer technology, etc., which gradually expose some shortcomings during the on-site construction process. For example, the casing patching technology has a low one-time operation success rate (only 68%), construction difficulties, limited pressure bearing (the maximum pressure bearing after the patching is 50MPa, and the pressure test is unstable in multiple well operations), affecting subsequent operations (metering equipment cannot enter the well, and multiple wells are blocked after the patching), and poor economic benefits of the patching (multiple perforation sections require multiple patching operations, and it is impossible to achieve combined production of new and old layers). The use of tubing + packer technology can achieve the combined production of two gases after construction, but the construction displacement is limited (≤6m 3 / min), the fracturing transformation effect is limited; and the operation risk is high, the RTTS packer is difficult to release, and the string is easy to get stuck, causing downhole accidents. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for dynamic chemical temporary plugging and wellbore reconstruction and fracturing transformation of old wells. The method is based on chemical temporary plugging technology and large-scale fracturing technology, which is conducive to the efficient utilization of coal-bearing gas resources.

[0006] The present invention is achieved by adopting the following technical solutions.

[0007] A method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, comprising the following steps:

[0008] S1: Analyze the fracturing production blocks and select old wells that meet the conditions for multi-gas co-production;

[0009] S2: Dynamic chemical plugging using degradable temporary plugging materials to achieve wellbore reconstruction;

[0010] S3: After successfully plugging the upper fractured layer, the lower reservoir is fractured;

[0011] S4: Degrade the temporary plugging materials of the blocked layer, restore gas production in the production layer, and produce gas together with the lower production layer.

[0012] Furthermore, in step S1, the production layer of the old well is a layer that has been fractured in the early stage, and the formation temperature is 50-60° C., which belongs to the category of low-temperature wells.

[0013] Furthermore, the specific method of step S2 is as follows:

[0014] a. Prepare the wellbore for flushing, requiring that there is no fallen objects or foreign matter left in the well and that it is clean;

[0015] b. Test the pressure, and after the pressure stabilizes, pump in 70 / 140 mesh quartz sand for sand filling. If the pressure rises suddenly, stop the pump and prepare to pump in temporary plugging materials;

[0016] c. Pump in 70 / 140 mesh quartz sand and powder and granular composite temporary plugging materials, and observe the changes in construction pressure. If the pressure rises rapidly and then drops, and then rises again and drops to a certain pressure and becomes stable, stop the pump and prepare for plugging again;

[0017] d. Pump in 40 / 70 mesh quartz sand and powder, granules, and knot composite temporary plugging materials for composite temporary plugging, and observe the changes in construction pressure. If the pressure rises significantly, or decreases slightly, and then rises again until it reaches 60MPa, stop the pump;

[0018] e. Conduct a test squeeze: Start the pump again. If the pressure rises quickly to 60MPa, stop the pump and start the pump again for a pressure test. If the pressure rises to 60MPa after three consecutive fracturing operations, it proves that plugging has been successfully achieved. If the pressure drops midway and does not meet the requirement, repeat step d until the pressure rises to 60MPa again.

[0019] Furthermore, the temporary plugging material is a polyvinyl alcohol-based chemical temporary plugging agent for fracturing. According to the required pressure and plugging time, the dissolution time is controlled by controlling the amount of the agent, the composition of the ingredients, and the particle size. The temporary plugging material can eventually be completely degraded into carbon dioxide and water, without causing damage to the formation and pollution to the environment.

[0020] Furthermore, the temporary plugging material is composed of a combination of different types and sizes, mainly including powders, granules, and knots.

[0021] Furthermore, the particle size of the powder type temporary plugging material is 100 mesh, the particle size of the granular temporary plugging material is 1.0-2.0mm, 3.0-4.0mm, and the size of the temporary plugging knot is 22mm, 26mm, and 32mm.

[0022] Furthermore, the powder and granular temporary plugging materials are mixed by the sand mixer and then carried by the fracturing fluid and pumped into the formation. The rope knot is directly pumped into the fracturing manifold with a pumping displacement of 1.0 to 1.5 m 3 / min.

[0023] Furthermore, the temporary plugging material meets the requirements of bearing pressure above 35MPa, not dissolving within 5 days at formation temperature, and completely dissolving within 5 days after adding sodium hydroxide solution. Specifically, the temporary plugging material is placed in the designed steel core, loaded into the core displacement device, and water injection displacement is started with annular pressure. Liquid may flow out at the beginning of the injection stage. When the liquid no longer flows out, the displacement pressure is gradually increased until the pressure of the liquid out again is the pressure that the temporary plugging agent can withstand. Indoor experiments have determined that the temporary plugging material used has no leakage at a pressure of 35MPa, which meets the requirements of on-site construction. The temporary plugging material is placed in a clean water ground-mouth bottle, placed in a constant temperature water bath at 50℃±1℃, and the timing is started. The dissolution of various temporary plugging materials at the formation temperature is observed. The experiment shows that the temporary plugging material is completely dissolved within 5 days after adding sodium hydroxide solution, and the solution is uniform, which meets the requirements of complete dissolution before fracturing and production, and will not affect the tools and tubing in the wellbore.

[0024] Furthermore, tracers are injected simultaneously during the temporary plugging material pumping process to monitor the degradation effect of the temporary plugging material at a later stage.

[0025] Furthermore, in step S3, the cementing quality of the lower fracturing target layer and the upper and lower 50 m layers thereof are both excellent or qualified, and can meet the requirements of the fracturing construction.

[0026] Furthermore, in step S3, the lower layer can be subjected to large-scale fracturing stimulation using bare casing + variable viscosity and slippery water, with a designed construction displacement of 16-18m 3 / min, during on-site fracturing, the construction parameters can be adjusted in time according to the changes in construction pressure. In order to prevent the high fracturing construction pressure and the failure to open the formation, the resistance reduction rate of viscous and slippery water is required to be greater than 70%.

[0027] Furthermore, in step S3, the fracturing of the lower layer can use high-viscosity liquid as the front fluid to form the main fracture, and alternately use low-viscosity liquid to carry 70 / 140 mesh quartz sand for grinding to reduce friction and filtration, and use medium-viscosity liquid as the sand-carrying fluid to form a volume fracture network. The main body uses a combination of 70 / 140 mesh quartz sand and 40 / 70 mesh quartz sand as a proppant, and 30 / 50 mesh quartz sand is used to seal the tail.

[0028] This application has the following beneficial effects.

[0029] (1) The dynamic chemical temporary plugging wellbore reconstruction and fracturing transformation method provided by the present invention is suitable for coal-measure gas reservoirs with superimposed occurrence characteristics such as coalbed methane, tight sandstone gas, and shale gas in the vertical direction;

[0030] (2) The post-fracturing reconstruction technology of the wellbore of the present invention not only helps to efficiently utilize the resources of multi-layer superimposed reservoirs, but also continues to release the production capacity of the original production layer, and is expected to provide a new scientific strategic decision-making basis for the coordinated development of multiple gas reservoirs;

[0031] (3) The method provided by the present invention uses temporary plugging materials of different types and combinations to temporarily plug the blastholes and near-wellbore fractures in the fractured layer, which can achieve precise temporary plugging between layers and create feasibility for repeated fracturing of old wells. Moreover, the plugging materials provided by the present invention can achieve 100% degradation after plugging, allowing the production layer of the old well to resume production. In addition, the process is simple, practical, low-cost, and the wellbore is full-diameter, which does not affect the later downhole operations. The temporary plugging materials used are eventually completely dissolved, realizing the release of reservoir production capacity again, and will not cause pollution to the environment.

[0032] (4) The present invention combines the advantages of chemical temporary plugging technology and large-scale fracturing process technology, which can not only realize the fracturing transformation of the new layer and the coordinated exploitation with the existing operating layer in the later stage, but also can be combined with well temperature logging and tracer monitoring technology to realize dynamic plugging effect monitoring and evaluation, and further verify the liquid inflow situation of the original layer after fracturing construction and the height of the new layer fracturing crack. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing of an old well according to Example 1 of the present invention;

[0034] Figure 2 It is a strength curve diagram of the temporary plugging material system of the present invention in the indoor pressure bearing test;

[0035] Figure 3 This is the construction curve of the field application of the dynamic chemical temporary plugging wellbore reconstruction method for old wells in Example 1 of the present invention. DETAILED DESCRIPTION

[0036] The present patent application is further described below in conjunction with embodiments.

[0037] Example 1

[0038] A method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, comprising the following steps:

[0039] (1) Analyze the production capacity of old wells that have been fractured in the block, and select old wells that can be used for multi-gas coordinated production, wherein the new production layer of the old well is located below the production layer that has been fractured and transformed in the early stage;

[0040] (2) Prepare the wellbore for flushing, requiring that there is no fallen objects or foreign matter left in the well and that it is clean;

[0041] (3) Pressure test: after the pressure stabilizes, pump in 70 / 140 mesh quartz sand for sand filling. If the pressure rises suddenly, stop the pump and prepare to pump in temporary plugging materials, where the temporary plugging materials are polyvinyl alcohol-based chemical temporary plugging materials for fracturing;

[0042] (4) Pump in 70 / 140 mesh quartz sand and powdered and granular composite temporary plugging materials, and inject tracers at the same time. If the pressure rises and the subsequent construction pressure gradually decreases and then stabilizes, stop the pump and prepare for plugging again;

[0043] (5) Pump in 70 / 140 mesh quartz sand and powder and granular composite temporary plugging materials again, along with tracer injection, and observe the changes in construction pressure. If the pressure rises rapidly and then drops, continue pumping and observe the pressure changes. If it rises again and then drops to a certain pressure and tends to stabilize, it means that the temporary plugging material has worked but has not achieved complete plugging. Stop the pump and prepare for plugging again.

[0044] (6) Pump in 40 / 70 mesh quartz sand and powder, granules, and knot composite temporary plugging materials for composite temporary plugging, and inject tracers at the same time to observe the changes in construction pressure. Among them, large-size particles bridge to form a skeleton, medium-size particles further fill, small-size powder temporary plugging materials adaptively plug pores, and knots temporarily plug the wellbore blastholes to improve the pressure bearing strength. Multiple temporary plugging materials work together. If the pressure rises significantly, or decreases slightly, and then rises again until 60MPa, stop the pump and enter the trial extrusion stage;

[0045] In steps (4), (5) and (6), the temporary plugging materials of powder (100 mesh) and granules (1.0-2.0 mm, 3.0-4.0 mm) are added by a sand mixer, stirred and pumped, and the rope knots (22-26 mm) are directly pumped from the fracturing manifold with a displacement of 1.0-1.5 m 3 / min;

[0046] (7) Test extrusion. Start the pump again. If the pressure rises quickly to 60 MPa, stop the pump and start the pump again to test the pressure. If the pressure rises to 60 MPa three times in a row, it proves that effective plugging has been successfully achieved. If the pressure drops midway and does not meet the requirement, repeat step (6) until the pressure rises to 60 MPa again.

[0047] (8) Perforation, followed by large-scale fracturing of the lower production layer with bare casing + variable viscous and slippery water. Among them, the variable viscous and slippery water uses the HaiLoong HVFR-1 variable viscous and slippery water system, with high-viscosity liquid used as the pre-flushing fluid to create the main fracture, and alternating low-viscosity liquid carrying 70 / 140 mesh quartz sand for grinding and reducing friction and filtration. The sand-carrying fluid uses medium-viscosity liquid to create a volume fracture network to increase the effective transformation area. Considering the improvement of the conductivity of fractures of different scales, the main body uses a combination of 70 / 140 mesh quartz sand and 40 / 70 mesh quartz sand as proppant, and the tail is 30 / 50 mesh quartz sand for sealing;

[0048] Table 1 shows the variable viscosity slippery water system used for fracturing reconstruction after dynamic chemical temporary plugging of old wells. The variable viscosity slippery water system can achieve mixing-free construction. The integrated variable viscosity agent, bactericide, and clay stabilizer are injected into the mixing tank of the sand mixer through the LAS liquid addition system according to construction requirements to achieve online mixing. During the construction process, the amount of integrated variable viscosity agent can be adjusted in real time according to the construction pressure and sand ratio to ensure construction safety.

[0049] Table 1 Slippery water system

[0050]

[0051] (9) The temporary plugging material in the upper plugging layer is completely dissolved, and the degradation effect of the plugging layer is verified based on the tracer monitoring results. The original production layer recovers its production capacity and achieves joint production with the lower newly fractured layer.

[0052] Figure 1 This is a schematic diagram of the method for dynamic chemical temporary plugging of old wells and reconstruction of fracturing. Temporary plugging materials of different types and sizes are used to achieve dynamic chemical temporary plugging of the target layer, and can be combined with well temperature logging technology to further verify the liquid inflow of the original layer after fracturing construction and the height of the new layer fracturing cracks.

[0053] Figure 3 This is the on-site application construction curve of the dynamic chemical temporary plugging wellbore reconstruction method for old wells described in Example 1 of the present invention. After successful plugging, the extrusion pressure increased to 60 MPa for three consecutive tests, proving that the scheme of the present invention can successfully achieve effective plugging.

[0054] The embodiments of this specific implementation method are all preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Therefore, all equivalent changes made based on the structure, shape, and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for dynamic chemical temporary plugging of wellbore reconstruction and fracturing of old wells, characterized by: The following steps are involved: S1: Analyze the fracturing production blocks and select old wells that meet the conditions for multi-gas co-production; S2: Dynamic chemical plugging using degradable temporary plugging materials to achieve wellbore reconstruction; S3: After successfully plugging the upper fractured layer, the lower reservoir is fractured; S4: Degrade the temporary plugging materials of the blocked layer, restore gas production in the production layer, and produce gas together with the lower production layer.

2. According to claim 1, a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, characterized in that: The specific method of step S2 is as follows: a. Prepare the wellbore for flushing, requiring that there is no fallen objects or foreign matter left in the well and that it is clean; b. Test the pressure, and after the pressure stabilizes, pump in 70 / 140 mesh quartz sand for sand filling. If the pressure rises suddenly, stop the pump and prepare to pump in temporary plugging materials; c. Pump in 70 / 140 mesh quartz sand and powder and granular composite temporary plugging materials, and observe the changes in construction pressure. If the pressure rises rapidly and then drops, and then rises again and drops to a certain pressure and becomes stable, stop the pump and prepare for plugging again; d. Pump in 40 / 70 mesh quartz sand and powder, granules, and knot composite temporary plugging materials for composite temporary plugging, and observe the changes in construction pressure. If the pressure rises significantly, or decreases slightly, and then rises again until it reaches 60MPa, stop the pump; e. Conduct a test squeeze: Start the pump again. If the pressure rises quickly to 60MPa, stop the pump and start the pump again for a pressure test. If the pressure rises to 60MPa after three consecutive fracturing operations, it proves that plugging has been successfully achieved. If the pressure drops midway and does not meet the requirement, repeat step d until the pressure rises to 60MPa again.

3. According to claim 1 or 2, a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, characterized in that: The temporary plugging material controls the dissolution time by controlling the applied dosage, component composition and particle size according to the required pressure and plugging time.

4. According to claim 1 or 2, a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, characterized in that: Temporary plugging materials are composed of different types and sizes, mainly including powders, granules and knots.

5. According to claim 1 or 2, a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, characterized in that: The powder and granular temporary plugging materials are mixed by the sand mixer and then carried by the fracturing fluid and pumped into the formation. The rope knot is directly pumped into the fracturing manifold with a pumping displacement of 1.0-1.5m 3 / min.

6. The method for dynamic chemical temporary plugging and wellbore reconstruction and fracturing transformation of an old well according to claim 1 or 2, characterized in that: The temporary plugging material was finally completely dissolved and the indoor test pressure was above 35MPa.

7. The method for dynamic chemical temporary plugging and wellbore reconstruction and fracturing transformation of an old well according to claim 1 or 2, characterized in that: During the pumping process of temporary plugging materials, tracers are injected simultaneously to monitor the degradation effect of temporary plugging materials at a later stage.

8. According to claim 1, a method for dynamic chemical temporary plugging of an old well and reconstruction and fracturing, characterized in that: In step S3, the fracturing pre-fluid of the lower layer uses a high-viscosity liquid to form the main fracture, and the low-viscosity liquid carries 70 / 140 mesh quartz sand for grinding and reducing friction and filtration. The sand-carrying fluid uses a medium-viscosity liquid to form a volume fracture network. The main body uses a combination of 70 / 140 mesh quartz sand and 40 / 70 mesh quartz sand as a proppant, and 30 / 50 mesh quartz sand is used to seal the tail.

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