Method for determining chemical flooding injection intensity and application

Abstract

The present application belongs to the technical field of oil and gas field development, and discloses a method for determining chemical flooding injection intensity and application, and the main steps include: analyzing the change rule of polymer detection concentration output by the production stage of the oil well of the well group and the water content of the well group, drawing the change rule curve, calculating and determining the reasonable limit of the polymer output concentration of the well group according to the trend line formula, analyzing the relationship between the polymer output concentration and the injection intensity, and finally determining the injection intensity of the single well and single layer. After the implementation, the daily oil production of the chemical flooding in Hushan area 3 reaches three times of that before the conversion, the water content reduction reaches more than 15%, the sand production of 1000 square meters of liquid volume is reduced from 3.0 square meters to 2.4 square meters, the pump detection cycle is increased from 213 days to 267 days, the chemical flooding effect is steadily rising, and meanwhile, the present application also provides a reference for the implementation of chemical flooding of similar or similar reservoirs.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, and relates to chemical composite flooding technology for enhanced oil recovery, specifically to a method for determining the injection intensity of chemical flooding and its application. Background Technology

[0002] Chemical flooding is a cutting-edge technology for the conversion and development of light oil. It involves adding chemicals to the injected water to alter the physicochemical properties of the displacing fluid and the interfacial properties between the displacing fluid and the crude oil and rock minerals, thereby improving crude oil production. It mainly includes polymer flooding, surfactant / polymer binary composite flooding, and alkali / surfactant / polymer ternary composite flooding, using agents such as polymers, surfactants, alkalis, and other auxiliary chemicals. Currently, China has the largest scale of chemical flooding operations in the world, placing it at a leading level. However, there are no precedents for large-scale chemical flooding implementation in sands reservoirs, and research on related technologies is still underway.

[0003] The reservoirs in the Shusan Block of Liaohe Oilfield are shallow (950-1700 meters), with poor compaction; the cementation type is mainly porous and contact cementation, resulting in loose cementation; and the clay content is high (13.9%). Affected by these reservoir factors, sand production is common in both oil and water wells, accounting for 93% of all wells. Especially after the implementation of chemical flooding in 2017 (6 injections and 17 productions), statistics on sand production in the polymer flooding area show that sand production in 10 wells has worsened, with the average pump inspection cycle decreasing from 344 days to 213 days, and the equivalent sand production per 10,000 cubic meters of produced fluid decreasing from 1.9 m³ / s. 3 Rise to 3.0m 3 As a result, production wells in well groups face difficulties in increasing fluid production and determining injection intensity, both of which negatively impact the effectiveness of chemical flooding. This study primarily focuses on developing a method to determine the injection intensity for chemical flooding in sand-producing reservoirs, thereby improving the development efficiency of chemical flooding.

[0004] A search of existing patent documents revealed no method for determining the injection intensity of chemical flooding in sandstone reservoirs. In current chemical flooding development, employing appropriate injection well injection intensities can significantly improve the effectiveness of chemical flooding; therefore, the method for determining the injection intensity in this invention is particularly important. Summary of the Invention

[0005] To fill the gap in the existing technology, the purpose of this invention is to address the problems of severe sand production in oil reservoirs, which leads to insufficient production volume in oil wells and unclear injection intensity in injection wells. The invention proposes a method for determining the injection intensity of chemical flooding, which is particularly suitable for chemical flooding in sand-producing reservoirs. Through the research and establishment of this method, it can be applied to the development of chemical flooding in sand-producing reservoirs to improve the implementation effect of chemical flooding.

[0006] The above-mentioned objective of this invention is achieved through the following technical solution:

[0007] A method for determining the injection intensity of chemical flooding involves analyzing the variation of polymer concentration and water cut in wells at different production stages within a well group, plotting the variation curves, calculating the reasonable limit of polymer production concentration for the well group based on the trend line formula, analyzing the relationship between polymer production concentration and injection intensity, and finally determining the injection intensity for a single well and a single layer.

[0008] Specifically, the following steps are included:

[0009] (1) Determine the relationship between the polymer detection concentration x in the oil well and the water cut change y1, and derive the theoretical formulas for x and y1 through the standard curve method to determine the critical value of polymer concentration when water cut increases;

[0010] (2) Determine the relationship between polymer detection concentration x and relative injection intensity y2 of injection well, derive the theoretical formulas for x and y2 using the standard curve method, and determine the upper limit of relative injection intensity of injection well;

[0011] (3) Determine the relationship between polymer detection concentration x and relative injection intensity y3 of injection well, and derive the theoretical formulas for x and y3 through the standard curve method to determine the upper limit of single-layer injection intensity of injection well.

[0012] Furthermore, the theoretical formulas for x and y1 in step (1) are: y1 = 0.0087x - 5.3487.

[0013] Furthermore, the theoretical formulas for x and y2 in step (2) are: y2 = 0.0025x + 1.6625.

[0014] Furthermore, the theoretical formulas for x and y3 in step (3) are: y3 = 0.0097x + 0.7168.

[0015] An application of a method for determining the injection intensity of chemical flooding is mainly used in chemical flooding of sand-producing reservoirs.

[0016] The advantages of this invention compared to the prior art are:

[0017] This invention provides a method for determining the injection intensity of chemical flooding, which is particularly suitable for determining the injection intensity of chemical flooding in sand-producing reservoirs and for determining the dynamic control range of the injection well. After implementation, the daily oil production of chemical flooding in the Shusan reservoir reached three times that before the conversion, the water cut decreased by more than 15%, the sand production per 10,000 cubic meters of liquid decreased from 3.0 cubic meters to 2.4 cubic meters, and the pump inspection cycle increased from 213 days to 267 days. The effect of chemical flooding has steadily improved, and it also provides a reference for the implementation of chemical flooding in similar reservoirs. Attached Figure Description

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Figure 1 It is a curve showing the change in polymer concentration versus water content;

[0020] Figure 2 This is a scatter plot showing the relationship between polymer detection concentration and relative injection intensity.

[0021] Figure 3 This is a scatter plot showing the relationship between polymer detection concentration and monolayer injection intensity. Detailed Implementation

[0022] To provide a clearer understanding of the technical features, objectives, and beneficial effects of this invention, the technical solution of this invention will now be described in detail with reference to the following specific embodiments. However, this should not be construed as limiting the scope of implementation of this invention. Unless otherwise specified, the experimental methods used in this invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used are all commercially available.

[0023] Example 1

[0024] This invention mainly includes the following two aspects:

[0025] First, the relative injection intensity limit for a single well was determined: Based on the relationship between the polymer concentration detected in the wells and the water cut variation in the chemical flooding pilot well group, a corresponding curve was plotted to clarify the upper limit formula for polymer concentration. Based on this, the polymer production concentration was calculated to be controlled within 615 mg / L, at which point the polymer flooding effect was better. Through the relationship curve between polymer detection concentration and relative injection intensity in a single well, the formula for single-well injection intensity was clarified, thus determining a reasonable range for polymer production concentration as a relative injection intensity of 3.2 mg / L in a single well. 3 Within / dm.

[0026] Second, the limit of single-layer injection intensity was determined: taking the strongly absorbent layer of the injection well where polymer cross-linking occurred as the research object, the relationship curve between polymer detection concentration and single-layer injection intensity was statistically analyzed, the variation law was analyzed, the calculation formula was derived, and finally the single-layer injection intensity was determined to be 6.68m. 3 Within / dm, the effect of controlling aggregation and cross-linking is relatively good.

[0027] The specific steps are as follows;

[0028] Determine the relationship curves between polymer detection concentration in polymer flooding production wells and water content, relative injection intensity of injection wells, and single-layer injection intensity.

[0029] (1) Determine the relationship between the detected concentration of polymer produced from the oil well and the change in water cut, and determine the critical value of polymer concentration when water cut increases. For example... Figure 1 As shown.

[0030] A theoretical formula y₁=0.0087x-5.3487 is obtained, wherein y₁ is the water cut change value and x is the detected polymer concentration. Substituting the zero water cut change value into the calculation formula, x=615 mg / L is obtained, and the relatively reasonable upper limit of polymer concentration is determined to be 615 mg / L.

[0031] (2) Determining the relationship between the detected polymer concentration and the relative injection intensity of injection wells, and determining the upper limit of the relative injection intensity of injection wells. As shown in Figure 2 , the point data in the figure are respectively derived from six wells: Shu 3-06-0005, Shu 3-5-507, Shu 3-05-506, Shu 3-05-5, 3-5-504 and Shu 3-5-04C.

[0032] A theoretical formula y₂=0.0025x+1.6625 is obtained, wherein y₂ is the relative injection intensity of a single well and x is the detected polymer concentration. Substituting the polymer concentration of 615 mg / L calculated in step (1) into the calculation formula, the upper limit of the relative injection intensity of a single well is obtained as 3.2 m 2 / (d·m).

[0033] (3) Determining the relationship between the detected polymer concentration and the single-layer injection intensity of injection wells, and determining the upper limit of the single-layer injection intensity of injection wells. As shown in Figure 2 , the point data in the figure are respectively derived from Shu 3-06-0005, Shu 3-05-506 and Shu 3-05-5.

[0034] A theoretical formula y₃=0.0097x+0.7168 is obtained, wherein y₃ is the relative single-layer injection intensity of a single well and x is the detected polymer concentration. Substituting the polymer concentration of 615 mg / L calculated in step (1) into the calculation formula, the upper limit of the relative single-layer injection intensity of a single well is obtained as 6.68 m 2 / (d·m).

[0035] The above is a calculation method for determining the injection intensity of chemical flooding in sand-producing reservoirs.

[0036] Example 2

[0037] At present, the present invention has been implemented in the chemical flooding test area of Shu 3 District, and the effect is being closely tracked.

[0038] In August 2017, a 6-well-group pilot test was carried out in Du 18 Block of Shu 3 District. In recent years, through determining the injection-production intensity and adjusting injection-production parameters, the current daily fluid production of the 6-well-group chemical flooding pilot test is 179 tons, the daily oil production is 45.8 tons, and the water cut is 74.4%. Compared with blank water flooding, the daily oil production increases by 30.3 tons and the water cut decreases by 17.8%. The sand production volume per 10,000 cubic meters of fluid decreased from 3.0 m³ to 2.4 m³, and the pump inspection period increased from 213 days to 267 days. The implementation effect of chemical flooding is remarkable.

[0039] Among them, the typical well group, Shu 3-05-5, saw a steady increase in fluid production after the injection intensity was adjusted. Daily fluid production increased from 49.4 tons to 73.4 tons, daily oil production increased from 7.7 tons to 20.3 tons, and water cut decreased from 84.0% to 72.3%, which helped the overall production of the chemical flooding well group to increase steadily.

[0040] The embodiments described above are merely preferred embodiments of the present invention, and not all feasible embodiments of the present invention. Any obvious modifications made by those 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 method for determining the chemical flooding injection intensity, characterized in that, The variation patterns of polymer concentration and water content in wells at different production stages were analyzed, variation curves were plotted, and the reasonable limits of polymer production concentration in the well group were calculated based on the trend line formula. The relationship between polymer production concentration and injection intensity was analyzed, and the injection intensity of a single well and a single layer was finally determined. Specifically, the following steps are included: (1) Determine the relationship between the polymer detection concentration x in the oil well and the water cut change y1. Obtain the theoretical formulas for x and y1 through the standard curve method. Substitute the water cut change y1 as zero into the theoretical formula to obtain the value of x and determine the critical value of polymer concentration when water cut increases. (2) Determine the relationship between polymer detection concentration x and relative injection intensity y2 of injection well, derive the theoretical formulas for x and y2 using the standard curve method, and determine the upper limit of relative injection intensity of injection well; (3) Determine the relationship between polymer detection concentration x and relative injection intensity y3 of injection well, derive the theoretical formulas for x and y3 using the standard curve method, and determine the upper limit of single-layer injection intensity of injection well; The theoretical formulas for x and y1 in step (1) are: ; The theoretical formulas for x and y2 in step (2) are: ; The theoretical formulas for x and y3 in step (3) are: .

2. An application of the method for determining the chemical flooding injection intensity as described in claim 1, characterized in that, It is applied to chemical flooding in sand-producing reservoirs.

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