A chemical flooding injection and production well unblocking process

Abstract

The present invention belongs to the technical field of oil production engineering blockage removal and discloses a chemical flooding injection and production well blockage removal process. The process includes permeability testing, determining the number of construction operations, fracturing, acidizing, displacement, pressure-release stratum support, temporary blockage, and circulation operations. Applicable to chemical flooding injection wells and water injection wells, the process can effectively reduce the injection pressure of chemical flooding injection wells, meet development and injection requirements, eliminate blockage problems in production wells, and increase production efficiency. The process utilizes a ball-throwing acid fracturing process, the core of which is a layer grading method, variable sand ratio and sand support, design of the number of soluble temporary plugging balls, and on-site operation methods. The process concept and overall construction design demonstrate a certain degree of creativity, reaching the domestic advanced level overall.

Description

Technical Field

[0001] The invention belongs to the technical field of oil production engineering blockage removal, and in particular relates to a chemical flooding injection and production well blockage removal process. Background Art

[0002] As an important non-renewable chemical energy source, petroleum has a significant impact on the national economy and national security. Relying on natural energy consumption for extraction (recovery rate of 5% to 10%) is called primary oil recovery, while artificial water (or gas) injection to maintain reservoir pressure (recovery rate of 30% to 40%) is called secondary oil recovery. However, as oil fields enter the late development stage with high water content, remaining recoverable reserves decrease and oil production declines more and more seriously. The adoption of new tertiary oil recovery methods is an important measure to increase recoverable reserves. Polymer flooding is one of the most important methods for improving oil recovery. During polymer flooding, a certain amount of high molecular weight polyacrylphthalamide or biopolymer xanthan gum is added to the injected water. However, the polymer itself is difficult to decompose. Over time, large amounts of polymer accumulate in the formation, causing formation blockage, resulting in dead wells without fluid production, and seriously affecting production.

[0003] At present, in order to solve the above problems, polymer plugging removers are generally used to degrade the large amount of polymers accumulated in the formation. Most of the existing polymer plugging removers are strong oxidants. The main principle is that strong oxidants can completely oxidize and decompose the main chain of the polymer, break the long chain of the macromolecule into multiple small molecular short chains, reduce the viscosity of the polymer and improve the fluidity of the polymer solution, thereby reducing or removing polymer blockages. However, strong oxidants cause serious damage to the formation and greatly enhance the water flow channel, causing the water content of the oil production to increase rapidly. Another common method is to use strong acid plugging removers. Acidizing plugging removal relies on the chemical dissolution of formation rocks and blockages by inorganic acids and organic acids and the hydraulic effect of acidizing pressure to improve the permeability of the formation. However, after the strong acid plugging remover is used, the strong acid will flow back into the wellbore, causing serious corrosion to the oil casing and lifting equipment.

[0004] At the same time, chemical flooding is an important replacement technology after the light oil block enters the "double high period". Shucai currently has 11 well groups flooded. As the development time prolongs, the contradiction between injection and production intensifies. The average pressure of the injection wells increases by 2.16MPa, showing a trend of injection difficulties. The average polymer content in the production wells is 1020mg / L, and the injection volume does not meet the requirements of the plan, which has a serious impact on the overall displacement effect of the chemical flooding. It is necessary to study a chemical flooding injection and production well unblocking process and operation method to alleviate, optimize and solve the chemical flooding injection and production contradiction. Summary of the Invention

[0005] In order to overcome the shortcomings of existing chemical flooding injection wells, such as increased pressure, injection volume failing to meet the requirements of the plan, and various degrees of pollution and corrosion of oil layers and equipment by unplugging agents, the present invention provides a chemical flooding injection and production well unplugging process. By utilizing the different fracture pressures between layers of the oil well, temporary plugging balls are used for unplugging operations. The unplugging device has a simple structure, safe construction, time-saving and labor-saving, and overcomes the difficulties of poor general fracturing transformation effect and easy blocking of mechanical stratification.

[0006] The above-mentioned object of the present invention is achieved through the following technical solution: a chemical flooding injection and production well unblocking process, the specific steps of which include:

[0007] 1. Detect the permeability of each oil layer in the oil well to be unblocked, and determine the number of operations based on the interlayer permeability ratio. If the ratio is ≤100, perform two operations; if the ratio is 100<ratio≤1000, perform three operations.

[0008] 2. Use guar gum fracturing fluid system to fracture the blocked oil layer, with a displacement of 4-5 cubic meters per minute, and the fracture extension radius is controlled within 1 / 2 of the distance to the oil well to be unblocked;

[0009] 3. Prepare a soil acid system of hydrochloric acid: hydrofluoric acid = 12%: 3%, with the balance being water, to acidify the blocked areas of the oil reservoir. The operation displacement should be the same as the displacement under the maximum wellhead pressure;

[0010] 4. Use guar gum fracturing fluid system to displace the oil reservoir blockage with acid at a displacement of 2 to 3 cubic meters per minute, and the displacement amount is 1 / 3 of the acid amount described in step 3;

[0011] 5. Use 40-70 mesh quartz sand to support the fractured layer produced by the hydraulic fracturing in step 2. The sand addition rate is 2-3 cubic meters per meter. The sand addition method is four-stage continuous. The first stage is 10% sand volume and the sand ratio is 15%. The second stage is 20% sand volume and the sand ratio is 25%. The third stage is 30% sand volume and the sand ratio is 30%. The fourth stage is 35% sand volume and the sand ratio is 35%.

[0012] 6. Use guar gum fracturing fluid to displace the blocked oil layer. The displacement volume is the same as the displacement volume during the sand addition in step 5, and the displacement volume is 1.25 times the wellbore volume;

[0013] 7. Pump temporary plugging balls into the pressure-opening layer described in step 5 for temporary plugging. The diameter of the temporary plugging balls is 1.5 times the diameter of the perforation corresponding to the pressure-opening layer, and the number of temporary plugging balls is 1.25 to 1.5 times the number of perforations in the pressure-opening layer. The temporary plugging balls are continuously pumped in with the guar gum fracturing fluid at a displacement of 4 to 5 cubic meters per minute.

[0014] 8. Change to another oil layer blockage and continue with steps 2 to 7 until the blockage is removed.

[0015] Furthermore, the temporary blocking ball in step 7 is made of polyvinyl alcohol with a density of 1 to 1.03 g / cm 3 , particle size 12 to 20 mm, maximum pressure resistance 65 MPa, water-soluble, effective pressure resistance time 72 hours, and complete degradation after 72 hours.

[0016] Compared with the prior art, the present invention has the following beneficial effects: the pipe string used for unblocking is simple in structure, and the construction is safe, time-saving and labor-saving. It is suitable for layers with poor cementing quality, casing deformation or layers that cannot be isolated with a packer, and is also suitable for oil layer transformation in open hole wells. It overcomes the difficulties of poor effect of general fracturing transformation and easy jamming of mechanical stratification; the chemical flooding injection and production well unblocking process of the present invention solves the contradiction between chemical flooding injection and production, maximizes the displacement effect of the chemical flooding well group, and has low cost and quick effect. After implementation, it is expected to be effective within 1-2 years; the temporary plugging balls used in the unblocking process can be suspended in the clean water displacement fluid. Since the water absorption capacity of the pressure-opened layer is greater than that of the unpressure-opened layer, the temporary plugging balls rely on this effect to embed into the corresponding blasthole of the pressure-opened layer during the displacement process, produce a plugging effect on it, and then perform secondary fracturing. By increasing the displacement and increasing the pressure, the fracturing construction of other oil layers can be achieved. This process is repeated continuously, taking into account the vertical development of the reservoir, to achieve the fracturing and plugging effect of different reservoirs. This application is applicable to chemical flooding injection wells and water injection wells, effectively reducing the injection pressure of chemical flooding injection wells, meeting development and injection requirements, eliminating production well blockage problems, and improving fluid production intensity. The ball-throwing acid fracturing process is centered on the treatment layer classification method, variable sand ratio and sand support, the design of the number of soluble temporary plugging balls, and the on-site operation method. It has a certain degree of creativity in the process concept and overall construction design, and has reached the domestic advanced level. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Figure 1 This is a schematic diagram of the use process of the guar gum fracturing fluid system of the present invention;

[0019] Figure 2 It is a schematic diagram of the degradation degree of the temporary blocking ball of the present invention over time. DETAILED DESCRIPTION

[0020] The present invention is described in detail below by specific examples, but the scope of protection of the present invention is not limited. Unless otherwise specified, the experimental methods adopted in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0021] Example 1

[0022] A chemical flooding injection and production well unblocking process, the specific steps are as follows:

[0023] A. Detect the permeability of each oil layer in the oil well to be unblocked, and determine the number of operations based on the interlayer permeability ratio;

[0024] B. Use guar gum fracturing fluid system (such as Figure 1 ) Fracturing the blocked oil layer with a displacement of 4 to 5 cubic meters per minute, and the fracture extension radius is controlled within 1 / 2 of the distance to the oil well to be unblocked;

[0025] C. Prepare a soil acid system of hydrochloric acid: hydrofluoric acid = 12%: 3%, with the balance being water, to acidify the blocked oil reservoir. The operation displacement should be the same as the displacement at the maximum wellhead pressure;

[0026] D. Use guar gum fracturing fluid system to carry out acid displacement, the construction displacement is 3 cubic meters / minute, and the displacement amount is 1 / 3 of the acid amount described in step C;

[0027] E. Use 40-70 mesh quartz sand to support the fractured layer produced by the hydraulic fracturing in step B. The sand addition rate is 3 cubic meters per meter. The sand addition method is four-stage continuous sand addition. The first stage is 10% sand volume and the sand ratio is 15%. The second stage is 20% sand volume and the sand ratio is 25%. The third stage is 30% sand volume and the sand ratio is 30%. The fourth stage is 35% sand volume and the sand ratio is 35%.

[0028] F. using guar gum fracturing fluid for displacement, the displacement volume is the same as the displacement volume during the sand addition in step E, and the displacement volume is 1.25 times the wellbore volume;

[0029] G. Use the guar gum fracturing fluid system to pump temporary plugging balls into the pressure-opening layer described in step E for temporary plugging. The diameter of the temporary plugging balls is 1.5 times the diameter of the perforation corresponding to the pressure-opening layer, and the number of temporary plugging balls is 1.25 times the number of perforations in the pressure-opening layer. The pumping method is to continuously pump the guar gum fracturing fluid at a displacement of 5 cubic meters per minute. The temporary plugging balls are made of polyvinyl alcohol with a density of 1g / cm 3 , particle size 20mm, maximum pressure resistance 65MPa, water-soluble substance, effective pressure resistance time 72 hours, completely degraded after 72 hours (such as Figure 2 );

[0030] H. Change to another oil layer blockage and continue with steps B to G until the blockage removal operation is completed.

[0031] Example 2

[0032] The Shu 3-5-504 well in the Du 18 block was selected for chemical flooding injection and production well unblocking operation.

[0033] In 2017, Well Shu 3-5-504 in Block Du-18 switched to chemical flooding. The displacement section was 1343.9-1407.4 meters, with a 25.6-meter per 13-layer structure and a daily injection rate of 48 cubic meters. The initial injection pressure was 12.5 MPa, but later rose to 20 MPa, preventing injection. Well A underwent temporary plugging and acidizing to deblock the section 1343.9-1387.7 meters deep. The section was 43.8 meters thick, with a perforation depth of 23 meters per 11 layers, reaching a medium depth of 1365.8 meters. This reservoir is a medium- to low-permeability tight sandstone reservoir.

[0034] Parameters of Shu 3-5-504 well in Du 18 block

[0035]

[0036] The specific steps for chemical flooding injection and production well unblocking operation are as follows:

[0037] Step 1: Pull out the tubing in the well and use clean water treated with the produced fluid in this block to flush the sand to the bottom of the artificial well.

[0038] Step 2: Use appropriate well clearing gauge to clear the well, and scrape the pipe 30 meters up and down 2-3 times at the pre-seating position of the fracturing packer, scraping and washing until clear water returns to the wellhead.

[0039] Step 3: Run the fracturing string, use the Y341 fracturing packer, set the seal at 30 meters above the top of the oil layer, avoiding the casing coupling, use the N80 external thickened fracturing tubing, the tubing specifications are selected according to the wellbore structure, and the fracturing wellhead uses the KL65-70 fracturing wellhead.

[0040] Step 4: After the wellhead is installed and the pressure test is passed, the unblocking process described in Example 1 is used to carry out unblocking construction.

[0041] Step 5: Start to blow out the pressure 4 hours after construction. Use a 3mm nozzle for blowout when the pressure is above 10MPa and a 5mm nozzle for blowout when the pressure is below 10MPa until the wellhead pressure reaches 0.

[0042] Step 6: Pull out the fracturing string in the well, use clean water treated with the produced fluid in this block to flush the sand to the bottom of the artificial well, and then lower the injection string or production string.

[0043] After temporary plugging and fracturing with acidizing agents to remove the blockage in Well A, four new water-absorbing zones were added, the injection pressure was reduced by 2 MPa, and 6,360 cubic meters of injection were injected, resulting in an increase in oil production of 402 tons per well group. This measure was highly effective, demonstrating the effectiveness of temporary plugging and fracturing with acidizing agents in removing blockages in chemical flooding injection-production wells.

[0044] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A chemical flooding injection and production well unblocking process, characterized in that: The following steps are involved: S1. Detect the permeability of each oil layer in the oil well to be unblocked. The number of operations is determined by the interlayer permeability ratio. If the ratio is ≤100, two operations are required. If the ratio is 100<ratio≤1000, three operations are required. S2. Fracturing the oil reservoir blockage using a guar gum fracturing fluid system, with the fracture extension radius controlled within 1 / 2 of the distance from the well to be unblocked; S3. Prepare a soil acid system to acidify the oil reservoir blockage. The operation rate is the same as the rate at the maximum wellhead pressure. S4. Use guar gum fracturing fluid system to displace the oil reservoir blockage with acid, displacing 1 / 3 of the amount of acid in step S3; S5. Quartz sand is used to support the pressure-opened layer produced by the fracturing in step S2. The sand addition rate is 2 to 3 cubic meters per meter. The sand addition method is four-stage continuous sand addition: the first stage is 10% sand, with a sand ratio of 15%, the second stage is 20% sand, with a sand ratio of 25%, the third stage is 30% sand, with a sand ratio of 30%, and the fourth stage is 35% sand, with a sand ratio of 35%; S6. Use guar gum fracturing fluid to displace the oil reservoir blockage, displacing the same displacement as during the step S5 sand addition, displacing an amount of 1.25 times the wellbore volume; S7. Pump temporary plugging balls into the pressure-opening layer described in step S5 for temporary plugging. The temporary plugging ball diameter is 1.5 times the diameter of the perforation corresponding to the pressure-opening layer, and the number of temporary plugging balls is 1.25 to 1.5 times the number of perforations in the pressure-opening layer. The pumping method is to continuously pump in guar gum fracturing fluid at a rate of 4 to 5 cubic meters per minute. S8. Change to another oil layer blockage and continue with steps S2 to S7 until the unblocking operation is completed.

2. The chemical flooding injection-production well unblocking process according to claim 1, characterized in that: The construction displacement of the guar gum fracturing fluid system in step S2 is 4 to 5 cubic meters per minute.

3. The chemical flooding injection-production well unblocking process according to claim 1, characterized in that: In step S3, the composition of the earth acid system is hydrochloric acid: hydrofluoric acid = 12%: 3%, and the balance is water.

4. The chemical flooding injection-production well unblocking process according to claim 1, characterized in that: The construction displacement of the guar gum fracturing fluid system in step S4 is 2 to 3 cubic meters per minute.

5. The chemical flooding injection-production well unblocking process according to claim 1, characterized in that: In step S5, the quartz sand has a mesh size of 40 to 70.

6. The chemical flooding injection-production well unblocking process according to claim 1, characterized in that: The temporary blocking balls used in step S7 are made of polyvinyl alcohol.

7. The chemical flooding injection-production well unblocking process according to claim 6, characterized in that: The density of the temporary blocking balls used in step S7 is 1-1.03 g / cm 3 , particle size 12~20mm, maximum pressure resistance 65MPa.

8. The chemical flooding injection-production well unblocking process according to claim 7, characterized in that: The temporary blocking balls used in step S7 have an effective pressure-resistant time of 72 hours.

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