A method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on Gini coefficient

Abstract

The present invention provides a method for quantitatively evaluating the equilibrium of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient, comprising: calculating the steam injection development temperature field by numerical simulation of the thermal recovery reservoir; taking a temperature greater than the initial reservoir temperature as the steam thermal front boundary, and drawing the boundary in a temperature field map; sequentially reading the grid coordinates of the steam injection well and the numerical simulation grid coordinates through which the steam thermal front boundary passes; sequentially calculating the distance between the steam injection well and the steam thermal front boundary coordinates according to the distance formula between two points on a plane; obtaining the minimum distance between the steam injection well and the steam thermal front boundary; respectively obtaining the distance between the circular boundary and the steam thermal front boundary; drawing the Lorentz curve of the distance between the circular boundary and the thermal front boundary; and obtaining the Gini coefficient G. The method for quantitatively evaluating the equilibrium of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient can effectively overcome the shortcomings of the traditional qualitative evaluation of the steam thermal front, and realizes the quantitative evaluation of the equilibrium of the steam thermal front.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield development, and in particular to a method for quantitatively evaluating the equilibrium of steam thermal front of thermal recovery oil reservoir based on Gini coefficient. Background Art

[0002] Since the 15th Five-Year Plan, Shengli Oilfield has developed supporting technologies such as heavy oil density throughput, super heavy oil, sensitive heavy oil, thermochemical throughput, thin layer, bottom water, shallow super heavy oil and heavy oil through technical research, and continuously strengthened the potential of old areas and investment in new areas, achieving a substantial increase in Shengli heavy oil production. By the end of 2017, Shengli Oilfield's heavy oil production reached 4.45 million tons, accounting for 19.1% of Shengli Oilfield's total production.

[0003] With the increase of production cycles, the effect of steam huff and puff gradually deteriorates. At the end of 2017, there were 1,225 steam huff and puff wells with 6 cycles or more in Shengli East Oilfield, accounting for 34.0% of the total number of wells. After entering the high-cycle huff and puff, the single well cycle oil production dropped to less than 1,200t, the cycle oil-gas ratio dropped to about 0.6, the cycle water content gradually increased to more than 90%, and the cycle effect gradually deteriorated. The heavy oil reservoir as a whole is in the stage of "high cycle, high water content, low production, low oil-gas ratio, medium-high recovery degree". Analyzing the reasons for the poor effect of high-cycle huff and puff, in addition to the cycle-by-cycle deterioration of the huff and puff effect caused by objective laws, unbalanced production is an important reason. The static heterogeneity of the reservoir and the dynamic heterogeneity of the development will lead to unbalanced production after high-cycle huff and puff. When the unbalanced production develops to the extreme, it will cause thermal interference between wells, affecting the production of oil wells, and seriously affecting the cycle production by more than 25%.

[0004] Steam flooding is the first choice and necessary replacement method after steam huff and puff, and has become a thermal recovery technology for large-scale industrial applications abroad. The heavy oil reservoir conditions in Shengli Oilfield are quite different from those in foreign countries. Shengli heavy oil is a marginal reservoir for steam drive and is difficult to develop. Since 74% of Shengli heavy oil thermal recovery reserves are in the Guantao Formation, the Guantao Formation oil layer is basically a fluvial phase deposit with strong reservoir heterogeneity. In addition, large flooded channels have been formed in some areas in the middle and late stages of huff and puff, so it is easy to cause uneven displacement and steam channeling during steam drive, which greatly affects the steam drive effect and improves the recovery rate.

[0005] Regardless of steam throughput or steam drive, due to the influence of reservoir heterogeneity and large water-oil mobility ratio, the uneven steam thermal front sweep is the main reason affecting the poor effects of high-cycle throughput development and steam drive development. Therefore, studying the steam thermal front sweep status and evaluating the thermal front sweep balance are the main aspects of improving steam sweep, increasing steam thermal utilization, improving the late stage of high-cycle throughput development, and regulating the steam drive development effect. In the past, there was rarely a quantitative evaluation of the steam sweep status, only a qualitative analysis, especially the thermal front sweep balance lacked a suitable quantitative evaluation method. Therefore, we invented a method for quantitatively evaluating the steam thermal front balance of thermal recovery reservoirs based on the Gini coefficient to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for quantitatively evaluating the equilibrium of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient, which fully considers technical and economic factors.

[0007] The object of the present invention can be achieved by the following technical measures: a method for quantitatively evaluating the balance of the steam thermal front of a thermal recovery oil reservoir based on the Gini coefficient, and the method for quantitatively evaluating the balance of the steam thermal front of a thermal recovery oil reservoir based on the Gini coefficient comprises: step 1, calculating the steam injection development temperature field by using the numerical simulation of the thermal recovery oil reservoir; step 2, taking the temperature greater than the initial reservoir temperature as the steam thermal front boundary, and drawing this boundary in the temperature field map; step 3, sequentially reading the grid coordinates of the steam injection well and the numerical simulation grid coordinates passed by the steam thermal front boundary; step 4, according to the distance formula between two points on the plane, sequentially calculating the distance between the steam injection well and the steam thermal front boundary coordinates; step 5, obtaining the minimum distance between the steam injection well and the steam thermal front boundary; step 6, respectively obtaining the distance between the circular boundary and the steam thermal front boundary; step 7, drawing the Lorentz curve of the distance d between the circular boundary and the thermal front boundary; step 8, obtaining the Gini coefficient G.

[0008] The purpose of the present invention can also be achieved by the following technical measures:

[0009] In step 3, the grid coordinates of the steam injection wells read in sequence are (x0, y0), and the numerical simulation grid coordinates of the steam thermal front boundary are (x i ,y i ).

[0010] In step 4, according to the distance formula between two points on a plane, the distance between the steam injection well and the boundary coordinates of the steam thermal front is calculated in sequence, which is recorded as D = {D1, D2, ..., D n}.

[0011] In step 5, the minimum distance between the steam injection well and the thermal front boundary is calculated, denoted as D min =min{D1,D2,……,D n}, with the steam injection well as the center, Dmin Draw a circle with the radius as the value and plot it in the temperature field diagram.

[0012] In step 6, the distances {D1, D2, ..., D n}-D min , denoted as d={d1,d2,……,d n}.

[0013] In step 7, the distances d between the circle boundary and the steam heat front boundary are sorted from large to small, and the corresponding grids on the boundary are numbered from 1 to n.

[0014] In step 7, the Lorentz curve of the distance d between the circle boundary and the thermal front boundary is calculated and plotted using formulas (1) and (2);

[0015] x m =100m / n (1)

[0016]

[0017] In the formula, d j represents the jth grid, x m ,y m It indicates that the mth grid corresponds to the point on the Lorentz curve, and n indicates the total number of steam front boundary grids.

[0018] In step 7, the greater the curvature of the Lorenz curve, the greater the distance difference between the steam front at different grids and the steam injection well, and the more unbalanced the steam front.

[0019] In step 8, the Gini coefficient G is defined as the concave area formed by the Lorenz curve AEC and the coordinate axis ABCD, that is, the ratio of the area of ​​AECD to the area of ​​the three bases ACD, as shown in formula (3):

[0020]

[0021] In the formula, area S ABCE The functional relationship f(x) of the curve AEC can be obtained by regression, and then it can be obtained by area integration. The upper and lower limits of the integration can be determined as [0, 100] according to the horizontal coordinate.

[0022] In step 8, the Gini coefficient G ranges from [0,1]. When the Gini coefficient is equal to 0, it means that the steam thermal front is equidistant from the steam injection well, forming a circle, indicating that the steam thermal front is absolutely balanced. When the Gini coefficient is equal to 1, it means that steam channeling occurs along the large pores or dominant seepage channels of the oil layer, and the steam thermal front is absolutely unbalanced.

[0023] The present invention provides a new method for describing the balance of the steam thermal front in the process of steam thermal recovery. On the basis of describing the temperature field development by numerical simulation of heavy oil thermal recovery, the steam thermal front boundary is taken as the temperature greater than the initial reservoir temperature, and the grid coordinates of the steam thermal front boundary are recorded in sequence, and the grid distance between the steam injection well and the steam thermal front boundary is calculated, and then the set of distances between the boundary of a circle with the minimum distance between the steam injection well and the steam thermal front boundary as the radius and the steam thermal front boundary is calculated, and finally the purpose of quantitatively evaluating the balance of the steam thermal front is achieved by drawing the Lorenz curve and calculating the Gini coefficient. This method can effectively overcome the shortcomings of the traditional qualitative evaluation of the steam thermal front and realize the quantitative evaluation of the balance of the steam thermal front. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the temperature field of the steam chamber of the oil reservoir after steam injection into the steam well in a specific embodiment of the present invention;

[0025] Figure 2 It is a schematic diagram of the steam thermal front boundary of the oil reservoir after steam injection into the steam well in a specific embodiment of the present invention;

[0026] Figure 3 It is a schematic diagram of the grid coordinates of the steam thermal front boundary of the reservoir and the grid coordinates of the steam well after steam injection in a specific embodiment of the present invention;

[0027] Figure 4 It is a schematic diagram of the distance between the steam well and the steam thermal front boundary in a specific embodiment of the present invention;

[0028] Figure 5 It is a schematic diagram of a circle whose radius is the minimum distance between the steam injection well and the thermal front boundary in a specific embodiment of the present invention;

[0029] Figure 6 A schematic diagram of obtaining the distance between a circle boundary and a steam heat front boundary in a specific embodiment of the present invention;

[0030] Figure 7 FIG. 4 is a Lorentz curve diagram of the distance between the circle boundary and the thermal front edge boundary in a specific embodiment of the present invention.

[0031] Figure 8 It is a flow chart of a specific embodiment of a method for quantitatively evaluating the balance of steam thermal front of a thermal recovery reservoir based on the Gini coefficient of the present invention;

[0032] Fig. 9 It is a schematic diagram of the steam thermal front boundary of a single well steam huff-and-puff development after the steam injection is completed in a specific embodiment of the present invention;

[0033] Fig.10 In a specific embodiment of the present invention, the steam thermal front boundary distance is calculated during the single well steam huff and puff development process.

[0034] Fig.11 It is a schematic diagram of the Lorentz curve of the thermal front boundary distance in single-well steam stimulation development in a specific embodiment of the present invention. DETAILED DESCRIPTION

[0035] In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings.

[0036] The method for quantitatively evaluating the balance of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient of the present invention is applicable to steam injection development of heavy oil reservoirs, including steam throughput, steam flooding, SAGD, etc. The method for quantitatively evaluating the balance of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient includes:

[0037] Step 1, using thermal recovery reservoir numerical simulation to calculate the steam injection development temperature field; Figure 1 shown.

[0038] Step 2: The temperature greater than the initial reservoir temperature is taken as the steam thermal front boundary, and this boundary is plotted in the temperature field diagram; Figure 2 shown.

[0039] Step 3: read the grid coordinates (x0, y0) of the steam injection well and the numerical simulation grid coordinates (x i ,y i );like Figure 3 shown.

[0040] Step 4: According to the distance formula between two points on a plane, calculate the distance between the steam injection well and the boundary coordinates of the steam thermal front in sequence, which is recorded as D = {D1, D2, ..., D n};like Figure 4 shown.

[0041] Step 5: Calculate the minimum distance between the steam injection well and the steam thermal front boundary, denoted as D min =min{D1,D2,……,D n}, and take the steam injection well as the center, D min Draw a circle with radius , and plot it in the temperature field diagram; Figure 5 shown.

[0042] Step 6: Calculate the distances {D1, D2, ..., D n}-D min , denoted as d={d1,d2,……,d n};like Figure 6 shown.

[0043] Step 7, draw the Lorentz curve of the distance d between the circular boundary and the thermal front boundary; sort the distance d between the circular boundary and the steam thermal front boundary from large to small, and number the corresponding grids on the boundary from 1 to n.

[0044] The Lorenz curve of the distance d between the circle boundary and the thermal front boundary is calculated and plotted using formulas (1) and (2). The greater the curvature of the curve, the greater the difference in distance between the steam front and the steam injection well at different grids (positions), and the more unbalanced the steam front.

[0045] x m =100m / n (1)

[0046]

[0047] In the formula, d j represents the jth grid, x m ,y m Indicates that the mth grid corresponds to a point on the Lorentz curve, and n indicates the total number of grids at the steam front boundary. Figure 7 shown.

[0048] Step 8, according to Figure 7 , on the basis of the Lorenz curve, the Gini coefficient G is obtained. In order to quantitatively analyze the curvature of the Lorenz curve and evaluate the balance of the steam thermal front, the Gini coefficient G of the Lorenz curve can be calculated for quantitative evaluation. The Gini coefficient G is defined as the concave area formed by the Lorenz curve and the coordinate axis, that is, the ratio of the area of ​​AECD to the area of ​​the three bases ACD, as shown in formula (3). The value range of the Gini coefficient G is [0,1]. When the Gini coefficient is equal to 0, it means that the distance between the steam thermal front and the steam injection well is equal, which is a circle, indicating that the steam thermal front is absolutely balanced; when the Gini coefficient is equal to 1, it means that steam channeling occurs along the large pores or dominant seepage channels of the oil layer, and the steam thermal front is absolutely unbalanced.

[0049]

[0050] In the formula, area S ABCE The functional relationship f(x) of the curve AEC can be obtained by regression, and then it can be obtained by area integration. The upper and lower limits of the integration can be determined as [0, 100] according to the horizontal coordinate.

[0051] This method is applicable to steam injection development of heavy oil reservoirs, and development methods include steam stimulation, steam flooding, SAGD, etc.

[0052] Figure 8 The present invention is a flow chart of a specific embodiment of the method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient.

[0053] In step 101, the temperature field after steam injection in the third cycle of single-well steam stimulation development is calculated using numerical simulation of thermal recovery reservoirs. The process proceeds to step 102.

[0054] In step 102, a temperature greater than the initial reservoir temperature of 60°C is taken as the steam thermal front boundary, and this boundary is plotted in the temperature field map, such as Fig. 9 The process proceeds to step 103.

[0055] In step 103, the grid coordinates of the steam injection well are read as (41, 41), and the coordinates of the numerical simulation grids through which the steam thermal front boundary passes are read in sequence (x i ,y i ), as shown in Table 1. The process proceeds to step 104.

[0056] In step 104, according to the distance formula between two points on a plane, the distance D between the steam injection well and the boundary coordinates of the steam thermal front is calculated in sequence, as shown in Table 1.

[0057] Table 1 Coordinates of the steam thermal front boundary grid, distance from the steam injection well, and distance from the circle boundary

[0058]

[0059]

[0060]

[0061]

[0062]

[0063]

[0064] The process enters step 105.

[0065] In step 105, the minimum distance between the steam injection well and the steam thermal front boundary is calculated, which is denoted as D min =15, the coordinate position is (41, 26), and the steam injection well is the center of the circle, D min Draw a circle with radius , and plot it in the temperature field diagram, such as Fig.10 The process proceeds to step 106.

[0066] In step 106, the circle boundary and the steam thermal front boundary grid (x i ,y i ) distance d = DD min ,like Fig.10 As shown in Table 1. The process proceeds to step 107.

[0067] In step 107, according to formulas (1) and (2), a Lorentz curve of the distance d between the circle boundary and the steam hot front boundary grid is drawn, as shown in Fig.11 The process proceeds to step 108 .

[0068] In step 108, binomial regression is performed on the Lorenz curve, and the regression formula is y = -0.0093x 2 +1.9164x+1.3662, R 2 =0.9999, according to formula (3), the Gini coefficient is:

[0069]

[0070] The results of calculating the Gini coefficient show that there is a strong imbalance in the steam thermal front of the well's steam intake and exhaust.

Claims

1. A method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient, characterized in that: The method for quantitatively evaluating the balance of the steam thermal front of a thermal recovery reservoir based on the Gini coefficient includes: Step 1, using thermal recovery reservoir numerical simulation to calculate the steam injection development temperature field; Step 2, taking the temperature greater than the initial reservoir temperature as the steam thermal front boundary, and drawing this boundary in the temperature field map; Step 3, sequentially reading the grid coordinates of the steam injection well and the numerical simulation grid coordinates through which the steam thermal front boundary passes; Step 4, according to the distance formula between two points on a plane, the distance between the steam injection well and the boundary coordinates of the steam thermal front is calculated in sequence; Step 5, calculating the minimum distance between the steam injection well and the steam thermal front boundary; Step 6, respectively calculating the distance between the circle boundary and the steam heat front boundary; Step 7, drawing a Lorentz curve of the distance between the circle boundary and the thermal front boundary; Step 8, calculate the Gini coefficient G; In step 7, the Lorentz curve of the distance d between the circle boundary and the thermal front boundary is calculated and plotted using formulas (1) and (2); x m =100m / n (1) In the formula, d j represents the jth grid, x m ,y m1 Indicates that the mth grid corresponds to the point on the Lorentz curve, and n represents the total number of grids at the steam front boundary; In step 7, the greater the curvature of the Lorenz curve, the greater the distance difference between the steam front at different grids and the steam injection well, and the more unbalanced the steam front; In step 8, the Gini coefficient G is defined as the concave area formed by the Lorenz curve AEC and the coordinate axis ABCD, that is, the ratio of the area of ​​AECD to the area of ​​the three bases ACD, as shown in formula (3): In the formula, area S ABCE The function relationship f(x) of the curve AEC is obtained by regression, and then it can be obtained by area integration. The upper and lower limits of the integral can be determined as [0, 100] according to the horizontal coordinate; In step 8, the Gini coefficient ranges from [0,1]. When the Gini coefficient is equal to 0, it means that the steam thermal front is equidistant from the steam injection well, forming a circle, indicating that the steam thermal front is absolutely balanced. When the Gini coefficient is equal to 1, it means that steam channeling occurs along the large pores or dominant seepage channels of the oil layer, and the steam thermal front is absolutely unbalanced.

2. The method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient according to claim 1, characterized in that: In step 3, the grid coordinates of the steam injection wells read in sequence are (x0, y0), and the numerical simulation grid coordinates of the steam thermal front boundary are (x i ,y i ).

3. The method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient according to claim 1, characterized in that: In step 4, according to the distance formula between two points on a plane, the distance between the steam injection well and the boundary coordinates of the steam thermal front is calculated in sequence, which is recorded as D = {D1, D2, ..., D n }.

4. The method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient according to claim 3, characterized in that: In step 5, the minimum distance between the steam injection well and the thermal front boundary is calculated, denoted as D min =min{D1,D2,……,D n }, with the steam injection well as the center, D min Draw a circle with the radius as the value and plot it in the temperature field diagram.

5. The method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient according to claim 4, characterized in that: In step 6, the distances {D1, D2, ..., D n }-D min , denoted as d={d1,d2,……,d n }.

6. The method for quantitatively evaluating the balance of steam thermal front in thermal recovery reservoirs based on the Gini coefficient according to claim 5, characterized in that: In step 7, the distances d between the circle boundary and the steam heat front boundary are sorted from large to small, and the corresponding grids on the boundary are numbered from 1 to n.

Images