Blockage removal process method

Abstract

The invention belongs to the field of oil exploitation, and discloses a plug removal process method, which comprises the following steps of: firstly, injecting a strong plug removal agent into a polymer flooding well to exert the strong effect of the strong plug removal agent on removing polymer plug, degrading wound polymer stickers step by step, greatly reducing the injection pressure, and laying a foundation for subsequently injecting a weak plug removal agent; and secondly, calculating the pollution volume of the polymer in combination with the blocking time of the polymer, namely the time when the injection pressure has an inflection point and rises quickly, injecting steam larger than the pollution volume, gradually degrading the weak blocking polymer at the edge at high temperature, and meanwhile, removing residual oil on pores of stratum rocks to avoid secondary blocking after recovery of polymer injection. And finally, an organic-inorganic composite blocking remover is injected, pollutants on the surface of reservoir rock are further cleaned, the wettability of the reservoir rock is changed, and better conditions are created for recovering polymer flooding and reducing re-blocking. The invention provides an effective solution for solving the blocking problem in the polymer flooding process.

Description

Technical Field

[0001] The present invention belongs to the field of oil exploitation, and relates to a plugging removal process method, specifically, a plugging removal process method for polymer plugging during the polymer flooding process in sandstone reservoirs. Background Art

[0002] In the Shusan District of Shuguang Oilfield, water flooding development is adopted. With the extension of the development time, it shows the characteristics of "double high" development, that is, the recovery degree of recoverable reserves reaches 81.0%, and the comprehensive water cut is 81.6%. The remaining oil between wells is scattered, and the thickness of medium and strong water flooded layers encountered by new wells in secondary development accounts for 59.8%. The water cuts of 14 new wells in the main flooded areas are all above 85% after production. After long-term water flooding development, the reservoir heterogeneity is aggravated, the dominant water flow channels are developed, and the three major contradictions of plane, interlayer and intrawell are prominent. It is difficult to further improve the recovery rate simply by water flooding development. Therefore, in combination with the reservoir characteristics and the remaining oil distribution characteristics, a polymer flooding technology test to improve the recovery rate is carried out. A pilot test of 11 well groups is carried out in the middle Du 18 well area. After the conversion to polymer flooding, the daily oil production is 72 tons, which is nearly 3 times that before the conversion. The comprehensive water cut is 74.7%, a decrease of 16.2% compared with water flooding. The annual oil production reached 22,000 tons in 2022, and the cumulative incremental oil in the stage was 36,000 tons. The effective proportion of chemical flooding oil wells reached 100%, an increase of 38% compared with water flooding. The multi-directional effective proportion reached 44%. Compared with the blank water flooding, the longitudinal utilization degree of injection wells increased from 45.2% to 72.9%, an increase of 27.7%. According to the current effect prediction, the ultimate recovery rate can reach 46.6%, an increase of 12.6% compared with water flooding and an increase of 2.3% compared with the design of the scheme.

[0003] However, with the in-depth progress of chemical flooding, some polymer injection wells have problems of sharp increase in injection pressure. Taking the well Shuguang 3-7-Geng 6 as an example, the initial injection pressure of polymer was 10 MPa. After 13 months, the injection pressure increased sharply to 17.3 MPa until injection could not continue and injection was stopped. Another example is the well Shuguang 3-5-504. The initial injection pressure of polymer was 10.5 MPa. After 15 months, the injection pressure rapidly climbed to 18.4 MPa, and then injection could not continue and injection was stopped. Therefore, it is urgent to study a plugging removal process method to solve the problem that the polymer plugging during the polymer flooding process causes the rapid increase in injection pressure of polymer injection and even injection failure.

[0004] Patent CN116218499A discloses a targeted breaker for oilfields and its preparation method; Patent CN112195018A discloses a non-oxidizing environmentally friendly and highly efficient plugging removal and depolymerization fluid; Patent CN106634915A discloses a polymer plugging removal agent for heavy oil wells; Patent CN105985759A discloses an oil well composite plugging removal agent and its preparation method; Patent CN101928557A discloses a plugging removal agent for polymer gel profile control agents. "Fault-Block Oil & Gas Field", No. 3, 2021, Development and Application of a High-Efficiency Composite Plugging Removal System in High Shaly Polymer Injection Areas; "Oil Drilling & Production Technology", No. 3, 2011, Causes of Plugging in Polymer Injection Wells and Plugging Removal Technologies; "Complex Hydrocarbon Reservoirs", No. 3, 2010, Development and Performance Evaluation of SYJ-1 Type Polymer Composite Plugging Removal Agent; "Inner Mongolia Petrochemical Industry", No. 4, 2014, Application of Two-Stage Plugging Removal and Pressure Reduction Process of Polymer in Gudong Oilfield.

[0005] The polymer plugging removal process methods mentioned in the above patents and articles involve removing polymer plugs by means of oxidative chain-breaking depolymerizing agents or non-oxidative depolymerizing agents. Some also use physical plugging removal methods or two-stage plugging removal methods, which have certain construction safety hazards, or the depolymerization effect is not ideal, the effective period is short, etc., affecting the implementation effect and promotion scale. Summary of the Invention

[0006] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a plugging removal process method for polymer plugs that is technically feasible, simple in construction, and has good measure effects.

[0007] The technical solution of the process method provided by the present invention is as follows:

[0008] Organically combine polymer plugging removal and polymer anti-plugging, and adopt the technical idea of "removing strong plugs in the center + removing weak plugs at the edge + changing wettability to prevent plugging" to form a polymer plugging prevention and removal technology, giving play to the advantages of triple plugging removal technologies and achieving the "two goals without relaxation" of plugging removal and anti-plugging. First, inject a strong plugging removal agent into the polymer flooding well to exert its strong effect of removing polymer plugs, gradually degrade the entangled polymer adhesives, and at the same time greatly reduce the injection pressure, laying a foundation for the subsequent injection of weak plugging removal agents. Second, combine the polymer plugging time, that is, starting from the time when the injection pressure shows an inflection point and rises rapidly, calculate the polymer pollution volume, and inject steam greater than the pollution volume to gradually degrade the weak plugging polymer at the edge at high temperature, and at the same time remove the residual oil on the pores of the formation rock to avoid secondary plugging after the resumption of polymer injection. Finally, inject an organic-inorganic composite plugging removal agent to further clean the pollutants on the surface of the reservoir rock and change its wettability, creating better conditions for the resumption of polymer flooding and reducing re-plugging.

[0009] The implementation steps of the plugging removal process method for the polymer plug are as follows:

[0010] 1. Removing strong central blockage: Inject a strong blockage remover into the polymer flooding well to exert its powerful depolymerizing agent effect and remove the polymer micelles entangled in the center. Its specific composition includes 0.3-8% depolymerizing agent + 3-5% clay stabilizer + 0.3-0.5% iron ion stabilizer + 0.3-0.6% corrosion inhibitor + 1-3% fungicide + 3-5% enhancer + the balance of water;

[0011] The depolymerizing agent includes one or more of sodium persulfate, potassium dichromate, ammonium persulfate, sodium dichromate, potassium permanganate, and sodium peroxodisulfate.

[0012] The enhancer includes one or more of hydrochloric acid, hydrofluoric acid, and fluoroboric acid.

[0013] The injection volume is calculated according to the following formula:

[0014]

[0015] Where V1 is the injection volume of strong plugging remover, unit is m 3 ; k is the maximum permeability of the oil layer, unit is mμm 2 ; P2 is the maximum value to which the pressure rises after polymer injection, unit: MPa; P1 is the pressure value before the pressure surge during polymer injection, unit: MPa; t is the time required for the pressure rise process, unit: month; h is the thickness of the main oil layer, unit: m.

[0016] The injection volume is generally 30-50m 3 , injection displacement is controlled at 0.2-0.4m 3 / min. If the construction team allows, try to reduce the displacement.

[0017] 2. Remove weak blockage at the edge: Use weak blockage remover to inject into polymer flooding wells. Its composition is high-temperature and high-pressure steam with a dryness of 70-75%. It can exert its high-temperature physical blockage removal effect and gradually degrade the weak blockage polymer at the edge at high temperature, thereby removing the weak blockage polymer at the edge.

[0018] The injection volume is calculated according to the following formula:

[0019]

[0020] Where V2 is the injection volume of weak plugging remover, unit: m 3 ; k is the maximum permeability of the oil layer, unit is mμm 2 ; P2 is the maximum value to which the pressure rises after polymer injection, unit: MPa; P0 is the pressure reference value before polymer injection, unit: MPa; t is the time required for the pressure rise process, unit: month.

[0021] The injection volume is generally 700-1000m 3, the injection displacement is controlled at 10 - 15 m 3 / h, and when permitted by the construction vehicle group, the displacement should be adjusted as large as possible.

[0022] 3. Transform wettability to prevent plugging. By using a transform wettability anti - plugging agent, further clean the pollutants on the surface of reservoir rocks and change their wettability, creating better conditions for restoring polymer flooding and reducing re - plugging. Its specific composition includes 3 - 5% HCl + 5 - 8% organic diacid + 3 - 5% organic polymer carboxylic acid + 5 - 8% fluoride salt + the balance of water;

[0023] Among them, the organic diacid includes one or more of adipic acid, oxalic acid, malonic acid, succinic acid, phenylacetic acid, phthalic acid, terephthalic acid, etc.

[0024] The organic polymer carboxylic acid includes one or more of polyacrylic acid, polymethacrylic acid, modified polyacrylic acid, polyepoxysuccinic acid, polyaspartic acid.

[0025] The fluoride salt includes one or more of potassium fluoride, sodium fluoride, potassium hydrogen fluoride, ammonium hydrogen fluoride, fluoboric acid, etc.

[0026] The injection volume is calculated according to the following formula:

[0027]

[0028] In the formula, V3 is the injection volume of the transform wettability anti - plugging agent, with the unit of m 3 ; a is the correction coefficient, which is positively correlated with the pressure value P1 before the sudden increase in pressure during the injection of polymer, and the value is P1 / 3; k is the highest permeability of the oil layer, with the unit of mμm 2 ; P2 is the highest value of the pressure after the injection of polymer, with the unit of MPa; P1 is the pressure value before the sudden increase in pressure during the injection of polymer, with the unit of MPa; t is the time required for the pressure to rise, with the unit of month; h is the thickness of the main oil layer, with the unit of m.

[0029] The injection volume is generally 90 - 150 m 3 , and the injection displacement is controlled at 0.2 - 0.4 m 3 / min, and when permitted by the construction vehicle group, the displacement should be adjusted as small as possible.

[0030] Compared with the prior art, the beneficial effects of the present invention are:

[0031] The present invention is reasonably designed and based on reliable grounds. Compared with the previous process method of solely injecting a polymer to relieve polymer plugging, it has three - fold plugging - removal technical advantages. It can relieve the strong plugging formed by the entanglement of polymer adhesives, the weak plugging formed by the bonding of polymer molecular chains with the formation, and at the same time clean the surface of reservoir rocks to prevent secondary plugging. It provides an effective solution to the plugging problem in the process of polymer flooding. Detailed implementation mode

[0032] The implementation of the present invention is given by the following examples. 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.

[0033] The following percentages are by mass.

[0034] Example 1

[0035] The polymer plugging and prevention combination technology for Well 3-5-04C in a certain oilfield. The construction is designed according to the above implementation steps:

[0036] In the first step, a strong plugging and plug removal agent is injected into the polymer flooding well. Its specific composition includes 3% ammonium persulfate + 2% sodium dichromate + 3% clay stabilizer + 0.3% iron ion stabilizer + 0.3% corrosion inhibitor + 1% bactericide + 3% hydrochloric acid + the balance of water. The injection volume is 45 cubic meters, and the injection pressure drops from 16 MPa to 9 MPa;

[0037] In the second step, a weak plugging and plug removal agent is injected into the polymer flooding well. Its composition is high-temperature and high-pressure steam with a dryness of 70 - 75%. The injection volume is 700 cubic meters, and the injection pressure is 15.5 MPa; In the third step, a wetting conversion and anti-plugging agent is used. Its specific composition includes 3% HCl + 5% oxalic acid + 3% phenylacetic acid + 3% polymethacrylic acid + 3.5% potassium fluoride + 2.5% fluoboric acid + the balance of water. The injection volume is 150 cubic meters, and the injection pressure is 8 MPa.

[0038] Before the measures, the polymer injection pressure of this well reached 16 MPa, which could not meet the requirement of the injection volume of 80 cubic meters, and only 30 cubic meters could be injected; after the measures, the polymer injection pressure of this well dropped to 9 MPa, meeting the requirement of the injection volume of 80 cubic meters, and the effective period has lasted for more than 1 year.

[0039] Example 2

[0040] The polymer plugging and prevention combination technology for Well 35504 in a certain oilfield. The construction is designed according to the above implementation steps:

[0041] In the first step, a strong plugging and plug removal agent is injected into the polymer flooding well. Its specific composition includes 3% sodium persulfate + 2% potassium dichromate + 4% clay stabilizer + 0.4% iron ion stabilizer + 0.5% corrosion inhibitor + 1.5% bactericide + 5% hydrofluoric acid + the balance of water. The injection volume is 50 cubic meters, and the injection pressure drops from 19 MPa to 13 MPa;

[0042] In the second step, a weak plugging removal agent is injected into the polymer flooding well. Its composition is high-temperature and high-pressure steam with a dryness of 70 - 75%, the injection volume is 950 cubic meters, and the injection pressure is 16.5 MPa. In the third step, a wetting transformation anti-plugging agent is used. Its specific composition includes 5% HCl + 5% malonic acid + 3% phthalic acid + 5% polyacrylic acid + 3% sodium fluoride + 5% fluoboric acid + the balance of water. The injection volume is 150 cubic meters, and the injection pressure is 11 MPa.

[0043] Before the measures, the polymer injection pressure of this well reached 18.4 MPa, resulting in the suspension of polymer injection due to the inability to inject. After the measures, the polymer injection pressure of this well dropped to 11 MPa, meeting the requirement of the injection volume of 80 cubic meters, and the effective period has lasted for more than 10 months.

[0044] The above has schematically described the present invention and its implementation manners, and this description is not restrictive. Therefore, if those of ordinary skill in the art are inspired by it and, without departing from the gist of the present invention, design similar structural manners and embodiments to this technical solution without creative efforts, they shall fall within the protection scope of the present invention.

Claims

1. A plugging removal process method, characterized in that, The following steps are involved: (1) Removing strong central blockage: injecting a strong blockage remover into the polymer flooding well, wherein the strong blockage remover comprises, by mass, 0.3-8% depolymerizer + 3-5% clay stabilizer + 0.3-0.5% iron ion stabilizer + 0.3-0.6% corrosion inhibitor + 1-3% bactericide + 3-5% enhancer + the balance of water; (2) Removing marginal weak blockage: injecting a weak blockage remover into the polymer flooding well, wherein the weak blockage remover comprises high-temperature and high-pressure steam with a dryness of 70-75% by mass; (3) Transformation wetting and anti-clogging: a transformation wetting and anti-clogging agent is used to further clean the surface pollutants of the reservoir rock. The transformation wetting and anti-clogging agent includes 3-5% HCl + 5-8% organic diacid + 3-5% organic polymer carboxylic acid + 5-8% fluoride salt + the balance water by mass.

2. The plugging removal process method according to claim 1, characterized in that, The depolymerizing agent includes one or more of sodium persulfate, potassium dichromate, ammonium persulfate, sodium dichromate, potassium permanganate, and sodium peroxodisulfate.

3. The plugging removal process method according to claim 1, wherein The enhancer includes one or more of hydrochloric acid, hydrofluoric acid, and fluoroboric acid.

4. The plugging removal process method according to claim 1, characterized in that The injection amount of strong plugging remover is calculated according to the following formula: Wherein, V1 is the injection volume of the strong plugging removal agent, unit: m 3 ; k is the maximum permeability of the oil reservoir, unit: mμm 2 ; P2 is the maximum value to which the pressure rises after injecting the polymer, unit: MPa; P1 is the pressure value before the sudden rise in pressure during the injection of the polymer, unit: MPa; t is the time required for the pressure to rise, unit: month; h is the thickness of the main oil reservoir, unit: m.

5. The plugging removal process method according to claim 1, characterized in that, The injection volume of the strong plugging removal agent is 30 - 50 m 3 , and the injection displacement is controlled at 0.2 - 0.4 m 3 / min.

6. The plugging removal process method according to claim 1, wherein, The injection amount of weak blockage remover is calculated according to the following formula: Wherein, V2 is the injection volume of the weak plugging and plug removal agent, with the unit of m 3 ; k is the maximum permeability of the oil reservoir, with the unit of mμm 2 ; P2 is the maximum value to which the pressure rises after polymer injection, in MPa; P0 is the pressure reference value before polymer injection, in MPa; t is the time required for the pressure rise process, in months.

7. The plugging removal process method according to claim 1, characterized in that, The injection volume of the weak plugging removal agent is 700 - 1000 m 3 , and the injection displacement is controlled at 10 - 15 m 3 / h.

8. The plugging removal process method according to claim 1, characterized in that, The organic diacid includes one or more of adipic acid, oxalic acid, malonic acid, succinic acid, phenylacetic acid, phthalic acid, terephthalic acid and the like.

9. The plugging removal process method according to claim 1, characterized in that, The organic polymeric carboxylic acid includes one or more of polyacrylic acid, polymethacrylic acid, modified polyacrylic acid, polyepoxysuccinic acid, and polyaspartic acid.

10. The plugging removal process method according to claim 1, characterized in that, Fluoride salts include one or more of potassium fluoride, sodium fluoride, potassium bifluoride, ammonium bifluoride, fluoroboric acid, and the like.

11. The plugging removal process method according to claim 1, characterized in that, The injection amount of transition wetting and anti-clogging agent is calculated according to the following formula: Wherein, V3 is the injection volume of the conversion wetting anti-blocking agent, with the unit of m 3 ; a is the correction coefficient, which is positively correlated with the pressure value P1 before the sudden increase in pressure during the polymer injection, and the value is P1 / 3; k is the highest permeability of the oil reservoir, with the unit of mμm 2 ; P2 is the maximum value to which the pressure rises after polymer injection, in MPa; P1 is the pressure value before the pressure surge during polymer injection, in MPa; t is the time required for the pressure rise process, in months; h is the thickness of the main oil layer, unit is m.

12. The plugging removal process method according to claim 1, characterized in that, The injection volume of the conversion wetting anti-blocking agent is generally 90 - 150 m 3 , and the injection displacement is controlled at 0.2 - 0.4 m 3 / min.

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