Method for determining top and bottom water invasion breakthrough pressure difference limit of steam huff and puff heavy oil reservoir

Abstract

The invention discloses a method for determining a top and bottom water invasion breakthrough pressure difference limit of a steam huff and puff heavy oil reservoir. The method comprises the steps that S1, the heating radius of steam huff and puff without considering the steam overlapping effect is determined; s2, using an elliptic equation to characterize the shape of the heating cavity considering the steam overlap effect; s3, representing the front edge position of the steam huff and puff heating cavity considering the steam overlapping effect; s4, steam huff and puff formation temperature distribution is obtained through calculation; s5, determining the viscosity distribution of the steam huff and puff stratum crude oil by using the viscosity-temperature curve; s6, determining steam huff and puff stratum crude oil starting pressure gradient distribution; and S7, the top and bottom water heavy oil reservoir breakthrough pressure difference limit is determined. The method can effectively guide high-efficiency development of heavy oil thermal recovery, and has important significance for guiding prevention of water invasion of top and bottom water of a heavy oil field and ensuring that development of the heavy oil field has a relatively good effect.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development, and in particular relates to a method for determining a pressure difference limit of top and bottom water invasion of a steam-huffing heavy oil reservoir. Background Art

[0002] The development of top and bottom water heavy oil reservoirs is difficult. During the development of such reservoirs, due to the combined effects of top water and bottom water, the risk of water invasion is relatively high. Regardless of whether top water invasion or bottom water invasion occurs, after water invasion, the water content of the oil field will increase significantly, and the production capacity of the oil field will be greatly reduced, resulting in low oil field recovery, poor development effect, and greater difficulty in post-water invasion management. The water source of water invasion in top and bottom water heavy oil reservoirs is top water or bottom water. When the pressure difference between the top water or bottom water and the throughput well is greater than the respective breakthrough pressure difference limit, water invasion will occur in the top and bottom water reservoirs. Therefore, determining the breakthrough pressure difference limit of top and bottom water invasion in steam throughput heavy oil reservoirs is of great significance for the prevention of top and bottom water invasion.

[0003] At present, the method for determining the pressure difference limit of water invasion breakthrough in top and bottom water heavy oil reservoirs is mainly to calculate the formation temperature distribution through numerical simulation, determine the reservoir start-up pressure gradient based on the temperature distribution, and then calculate the pressure difference limit. This method can characterize the non-uniform distribution of formation temperature after steam stimulation, but fails to consider the influence of steam overburden on the steam stimulation heating chamber, resulting in inaccurate understanding of the pressure difference limit of water invasion breakthrough in top and bottom water heavy oil reservoirs. Summary of the invention

[0004] The present invention is proposed to solve the problems existing in the prior art, and its purpose is to provide a method for determining the pressure difference limit of top and bottom water invasion in steam-huffing heavy oil reservoirs.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for determining the pressure difference limit of top and bottom water invasion of a steam-stimulated heavy oil reservoir comprises the following steps:

[0007] S1. Determine the heating radius of steam throughput without considering the steam overburden effect.

[0008] When the steam overburden effect is not considered, the shape of the heating cavity of steam huff and puff is circular. Based on the reservoir physical parameters of the target block, the heating radius is calculated using the calculation formula of the steam huff and puff heating radius at the end of steam injection. The calculation formula of the steam huff and puff heating radius at the end of steam injection is:

[0009]

[0010] Where: r h is the steam heating radius at the end of steam injection, in m; i sis the mass flow rate of water vapor, in kg / s; x is the steam quality, no; l v is the latent heat of vaporization of steam, in kJ / kg; h sw is the enthalpy of hot water at steam temperature, in kJ / kg; h rw is the enthalpy of hot water at reservoir temperature, in kJ / kg; dL is the length of the microelement of the horizontal well, in m; M R is the heat capacity of the oil layer, in kJ / (m 3 ·℃); t s is the injection steam temperature, in °C; t r is the original formation temperature, in °C; τ is the production time, in s.

[0011] S2. Use the elliptic equation to characterize the shape of the heating chamber considering the steam overburden effect.

[0012] After considering the steam overburden effect, the shape of the heating chamber of the steam huff and puff is no longer circular, but approximately elliptical. Therefore, the elliptical equation is used to characterize the shape of the heating chamber considering the steam overburden effect. The characterization equation is:

[0013]

[0014] Where: x represents the horizontal coordinate of the ellipse, in m; z represents the vertical coordinate of the ellipse, in m; a represents the length of the minor axis of the ellipse, in m; b represents the length of the major axis of the ellipse, in m; m represents the distance from the center of the ellipse to the origin of the coordinate system, in m;

[0015] When steam is injected into the formation, due to the effect of buoyancy, steam overburden occurs. According to the theory of seepage mechanics, the relationship between a, b, and m can be expressed as:

[0016]

[0017] In formula (4) to formula (5), ΔP represents the production pressure difference, in MPa; Δρ represents the density difference between steam and crude oil, in kg / m 3 ; g represents the acceleration due to gravity, the unit is m / s 2 .

[0018] S3. Characterize the leading edge position of the steam-throwing heating chamber considering the steam overburden effect.

[0019] Combined with the steam heating radius calculated in step S1, the values ​​of a, b, and m in step S2 are calculated according to the volume balance principle before and after considering the steam overburden effect. The volume balance equation is:

[0020]

[0021] The values ​​of a, b, and m can be obtained by combining equations (3) to (5). Substituting the values ​​of a, b, and m into equation (2) can obtain the leading edge position of the steam-throwing heating chamber taking into account the steam overburden effect.

[0022] S4. Calculate the formation temperature distribution during steam injection.

[0023] The formation temperature within the steam stimulation heating range obtained in step S3 is calculated using the formation temperature distribution calculation formula. The temperature within the steam stimulation heating range decreases linearly from the bottom of the wellbore to the front edge of the heating chamber. The formation temperature distribution calculation formula within the heating chamber range is:

[0024]

[0025] Where: T h (r) is the formation temperature at a distance r from the wellbore, in °C; T i is the temperature of the injected steam, in °C; T 0 is the original formation temperature, in °C; r is the distance from the huff-and-puff well, in m; r h is the steam throughput heating radius at the end of steam injection, in m;

[0026] The formation temperature distribution within the heating range can be calculated by formula (6), and the formation temperature outside the heating range is the original formation temperature distribution.

[0027] S5. Use the viscosity-temperature curve to determine the viscosity distribution of the crude oil during steam stimulation.

[0028] Based on the steam stimulation formation temperature distribution obtained in step S4, the viscosity distribution of crude oil in the steam stimulation formation is determined by comparing the viscosity-temperature curve of the target block.

[0029] S6. Determine the start-up pressure gradient distribution of the formation crude oil during steam stimulation.

[0030] Based on the formation crude oil viscosity distribution obtained in step S5, the start-up pressure gradient distribution is determined using the target block start-up pressure gradient characterization formula. The target block start-up pressure gradient characterization formula is:

[0031]

[0032] Where: G o is the starting pressure gradient of the formation crude oil, in MPa / m; K o is the effective permeability of formation crude oil, in mD; μ o is the viscosity of the formation crude oil, in mPa·s; M and N are coefficients and are dimensionless.

[0033] S7. Determine the breakthrough pressure difference limit of top and bottom water heavy oil reservoirs.

[0034] Based on the formation crude oil start-up pressure gradient distribution determined in step S6, the breakthrough pressure difference limits of top water and bottom water are calculated respectively:

[0035] The calculation formula for the breakthrough pressure difference limit of top water is:

[0036]

[0037] The calculation formula for the breakthrough pressure difference limit of bottom water is:

[0038]

[0039] In formula (8) and (9): ΔP u is the limit of the top water breakthrough pressure difference, in MPa; r is the distance from each position to the horizontal well in the integral calculation, in m; r f is the wellbore radius, in m; r u is the distance between the horizontal well and the top water, in m; ρ o is the density of crude oil, in kg / m 3 ; ΔP l is the bottom water breakthrough pressure difference limit, in MPa; r l is the distance between the horizontal well and the bottom water, in meters; G o is the starting pressure gradient of the formation crude oil, in MPa / m; g represents the acceleration of gravity, in m / s 2 ;

[0040] Using formula (8), the top water breakthrough pressure difference limit ΔP can be calculated u , using formula (9) to calculate the bottom water breakthrough pressure difference limit ΔP l The breakthrough pressure difference limit of top water and bottom water is the minimum value of the breakthrough pressure difference limit of top water and bottom water min(ΔP u , ΔP l ).

[0041] The beneficial effects of the present invention are:

[0042] The present invention provides a method for determining the pressure difference limit of top and bottom water invasion of heavy oil reservoirs during steam stimulation. On the basis of calculating the heating radius of steam stimulation, a method for characterizing the shape of a heating cavity taking into account the steam overburden effect is established. In combination with a starting pressure gradient calculation formula, a characterization model of top and bottom water invasion during steam stimulation is established based on the seepage mechanics theory. A method for determining the pressure difference limit of top and bottom water invasion of heavy oil reservoirs during steam stimulation is formed. The method can effectively guide the efficient development of heavy oil thermal recovery, and is of great significance for guiding the prevention of top and bottom water invasion in heavy oil fields and ensuring that good results are achieved in the development of heavy oil fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 is a flow chart of the method of the present invention;

[0044] Figure 2 This is a diagram of the shape of the heating chamber in the present invention taking into account the steam overburden effect;

[0045] Figure 3 It is a temperature distribution diagram of each position of the steam stimulation formation in the present invention;

[0046] Figure 4 It is the viscosity-temperature curve diagram of the present invention;

[0047] Figure 5 It is a crude oil viscosity distribution diagram at each position of the steam stimulation formation in the present invention;

[0048] Figure 6 It is a startup pressure gradient distribution diagram of the steam throughput heating chamber along the long axis direction in the present invention.

[0049] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0050] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0051] Example 1

[0052] The calculation of the ultimate pressure difference of water invasion at the top and bottom of a heavy oil reservoir with steam stimulation is carried out based on the basic parameters of a certain reservoir. The basic parameters are: reservoir temperature is 56℃, reservoir thickness is 61m, average porosity is 30.8%, and average permeability is 2980×10 -3 μm 2 , the crude oil viscosity is 39862mPa·s, and the original formation pressure is 12.1MPa. Figure 1 As shown, the present invention provides a method for calculating the ultimate pressure difference of top and bottom water invasion breakthrough of steam stimulation heavy oil reservoir, comprising:

[0053] S1. Determine the heating radius of steam huff and puff without considering the steam overburden effect. When the steam overburden effect is not considered, the shape of the heating cavity of the steam huff and puff is circular. Based on the reservoir physical properties of the target block, the heating radius is calculated using the calculation formula for the heating radius of steam huff and puff at the end of steam injection. The calculation formula for the heating radius of steam huff and puff at the end of steam injection is:

[0054]

[0055] In the formula, i s is the steam injection rate, kg / s; x is the steam dryness; l v is the latent heat of vaporization of steam, kJ / kg; h swis the enthalpy of hot water at steam temperature, kJ / kg; h rw is the enthalpy of hot water at reservoir temperature, kJ / kg; M R is the heat capacity of the oil layer, kJ / (m 3 ·℃); t s is the temperature of injected steam, °C; t r is the original formation temperature, ℃; τ is the production time, s.

[0056] The steam velocity of the target block is 3.35 kg / s, the injected steam quality is 0.4, the injected steam temperature is 350 ° C, the latent heat of vaporization of steam is 878 kJ / kg, the enthalpy of hot water at steam temperature is 3630 kJ / kg, the enthalpy of hot water at reservoir temperature is 1120 kJ / kg, and the heat capacity of the oil layer is 1.87 J / (m 3 ·℃), and the steam heating radius without considering the steam overburden effect is calculated using formula (2) to be 31m.

[0057] S2. Use the elliptical equation to characterize the shape of the heating chamber considering the steam overburden effect. After considering the steam overburden effect, the shape of the heating chamber of the steam intake and exhaust is no longer circular, but approximately elliptical. Therefore, the elliptical equation is used to characterize the shape of the heating chamber considering the steam overburden effect. The characterization equation is:

[0058]

[0059] Where a represents the length of the minor axis of the ellipse, b represents the length of the major axis of the ellipse, and m represents the distance from the center of the ellipse to the origin of the coordinate system.

[0060] When steam is injected into the formation, due to the effect of buoyancy, steam overburden occurs. According to the theory of seepage mechanics, the relationship between a, b, and m can be expressed as:

[0061]

[0062] In formula (4) to formula (5), ΔP represents the production pressure difference, Pa; Δρ represents the density difference between steam and crude oil, kg / m 3 ; g represents the acceleration due to gravity, m / s 2 .

[0063] The heating chamber shape considering the steam overburden effect is characterized by using the elliptic equation as shown in Figure 2 shown.

[0064] S3. Characterize the leading edge position of the steam huff and puff heating chamber considering the steam overburden effect. Combined with the steam huff and puff heating radius calculated in the first step, the coefficients a, b, and m in the second step are calculated based on the volume balance principle before and after considering the steam overburden effect. The volume balance equation is:

[0065]

[0066] The values ​​of a, b, and m can be obtained by combining equations (3) to (5). Substituting the values ​​of a, b, and m into equation (2) can obtain the leading edge position of the steam-throwing heating chamber taking into account the steam overburden effect.

[0067] The production pressure difference of the target block is 3MPa, and the density difference between steam and crude oil is 860kg / m 3 , the acceleration due to gravity is 9.8 m / s 2 , combining equations (3) to (5), we get the value of a is 21, the value of b is 46, and the value of m is 3. Substituting the values ​​of a, b, and m into equation (2), we get:

[0068]

[0069] The above formula is a characterization equation for the leading edge position of the steam-puff heating chamber taking into account the steam overburden effect.

[0070] S4. Calculate the formation temperature distribution of steam stimulation. Use the formation temperature distribution calculation formula to calculate the formation temperature within the steam stimulation heating range obtained in the third step. The temperature within the steam stimulation heating range decreases linearly from the bottom of the well to the front edge of the heating chamber. The formation temperature distribution calculation formula within the heating chamber range is:

[0071]

[0072] Where, T h (r) is the formation temperature at a distance r from the throughput well, °C; T i is the temperature of injected steam, °C; T 0 is the original formation temperature, ℃; r is the distance from the huff-and-puff well, m.

[0073] The formation temperature distribution within the heating range can be calculated by formula (6). The formation temperature outside the heating range is the original formation temperature distribution. The temperature distribution of each position of the formation during steam stimulation is calculated as follows: Figure 3 shown.

[0074] S5. Determine the viscosity distribution of the steam stimulation formation crude oil using the viscosity-temperature curve. Based on the steam stimulation formation temperature distribution obtained in the fourth step, the viscosity distribution of the steam stimulation formation crude oil is determined by comparing the viscosity-temperature curve of the target block.

[0075] The viscosity-temperature curve of the target block is as follows: Figure 4 As shown, combined with the formation temperature distribution obtained in the fourth step, the formation crude oil viscosity distribution is determined as follows Figure 5 shown.

[0076] S6. Determine the startup pressure gradient distribution of the formation crude oil in steam stimulation. Based on the formation crude oil viscosity distribution obtained in step 5, the startup pressure gradient distribution is determined using the target block startup pressure gradient characterization formula. The target block startup pressure gradient characterization formula is:

[0077]

[0078] In the formula, G o is the starting pressure gradient of formation crude oil, MPa / m; K o is the effective permeability of formation crude oil, mD; μ o is the viscosity of formation crude oil, mPa·s; M and N are coefficients.

[0079] The target block coefficient M is -0.0848, the coefficient N is 0.1887, and the starting pressure gradient distribution of the steam heating chamber along the long axis direction is calculated using formula (7): Figure 6 shown.

[0080] S7. Determine the breakthrough pressure difference limit of the top and bottom water heavy oil reservoir. Based on the formation crude oil start-up pressure gradient distribution determined in step 6, calculate the breakthrough pressure difference limits of the top water and bottom water respectively, and the calculation formulas are:

[0081]

[0082] Where ΔP u is the pressure difference limit of top water breakthrough, MPa; r f is the wellbore radius, m; r u is the distance between the horizontal well and the top water, m; ρ o is the density of crude oil, kg / m 3 ; ΔP l is the bottom water pressure difference limit, MPa; r l is the distance between the horizontal well and the bottom water, m.

[0083] Using formula (8), the top water breakthrough pressure difference limit ΔP can be calculated u , using formula (9) to calculate the bottom water breakthrough pressure difference limit ΔP l The breakthrough pressure difference limit of top water and bottom water is the minimum value of the breakthrough pressure difference limit of top water and bottom water min(ΔP u , ΔP l ).

[0084] The top water breakthrough pressure difference limit calculated by formula (8) is 5.66 MPa, and the bottom water breakthrough pressure difference limit calculated by formula (9) is 6.34 MPa. Therefore, under the current production conditions, the top and bottom water breakthrough pressure difference limit of the target oil field is 5.66 MPa.

[0085] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for determining the pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir, characterized in that: The following steps are involved: S1. Determine the heating radius of steam throughput without considering the steam overburden effect; S2. Use elliptic equations to characterize the shape of the heating chamber considering the steam overburden effect; S3. Characterize the leading edge position of the steam huff-and-puff heating chamber considering the steam overburden effect; S4, calculating and obtaining the formation temperature distribution of steam stimulation; S5. Determine the viscosity distribution of the crude oil in the steam stimulation formation using the viscosity-temperature curve; S6. Determine the start-up pressure gradient distribution of the crude oil in the formation by steam stimulation; S7. Determine the breakthrough pressure difference limit of top and bottom water heavy oil reservoirs.

2. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method of determining the heating radius of the steam throughput without considering the steam overburden effect in step S1 is: Based on the reservoir physical property parameters of the target block, the heating radius is calculated using the steam huff and puff heating radius calculation formula at the end of steam injection. The steam huff and puff heating radius calculation formula at the end of steam injection is: Where: r h is the steam heating radius at the end of steam injection, in m; i s is the mass flow rate of water vapor, in kg / s; x is the steam quality, no; l v is the latent heat of vaporization of steam, in kJ / kg; h sw is the enthalpy of hot water at steam temperature, in kJ / kg; h rw is the enthalpy of hot water at reservoir temperature, in kJ / kg; dL is the length of the microelement of the horizontal well, in m; M R is the heat capacity of the oil layer, in kJ / (m 3 ·℃); t s is the injection steam temperature, in °C; t r is the original formation temperature, in °C; τ is the production time, in s.

3. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The step S2 uses an elliptic equation to characterize the shape of the heating chamber considering the steam overlay effect: Where: x represents the horizontal coordinate of the ellipse, in m; z represents the vertical coordinate of the ellipse, in m; a represents the length of the minor axis of the ellipse, in m; b represents the length of the major axis of the ellipse, in m; m represents the distance from the center of the ellipse to the origin of the coordinate system, in m; According to the seepage mechanics theory, the relationship between a, b and m is expressed as: In formula (4) to formula (5), ΔP represents the production pressure difference, in MPa; Δρ represents the density difference between steam and crude oil, in kg / m 3 ; g represents the acceleration due to gravity, the unit is m / s 2 .

4. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method of step S3 for characterizing the leading edge position of the steam huff-and-puff heating chamber considering the steam overburden effect is: Combined with the steam heating radius calculated in step S1, the values ​​of a, b, and m in step S2 are calculated according to the volume balance principle before and after considering the steam overburden effect. The volume balance equation is: The values ​​of a, b, and m are obtained by combining equations (3) to (5). Substituting the values ​​of a, b, and m into equation (2) yields the leading edge position of the steam-throwing heating chamber taking into account the steam overburden effect.

5. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method of calculating the formation temperature distribution by steam stimulation in step S4 is: The formation temperature within the steam stimulation heating range obtained in step S3 is calculated using the formation temperature distribution calculation formula. The temperature within the steam stimulation heating range is linearly reduced from the bottom of the wellbore to the front edge of the heating chamber. The formation temperature distribution calculation formula within the heating chamber range is: Where: T h (r) is the formation temperature at a distance r from the wellbore, in °C; T i is the temperature of the injected steam, in °C; T0 is the original formation temperature, in °C; r is the distance from the huff-and-puff well, in m; r h is the steam throughput heating radius at the end of steam injection, in m; The formation temperature distribution within the heating range is calculated by equation (6), and the formation temperature outside the heating range is the original formation temperature distribution.

6. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method of using the viscosity-temperature curve to determine the viscosity distribution of the steam-stimulated formation crude oil in step S5 is: based on the steam-stimulated formation temperature distribution obtained in step S4, the viscosity distribution of the steam-stimulated formation crude oil is determined by comparing the viscosity-temperature curve of the target block.

7. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method of determining the start-up pressure gradient distribution of the formation crude oil by steam stimulation in step S6 is: Based on the formation crude oil viscosity distribution obtained in step S5, the start-up pressure gradient distribution is determined using the target block start-up pressure gradient characterization formula. The target block start-up pressure gradient characterization formula is: Where: G o is the starting pressure gradient of the formation crude oil, in MPa / m; K o is the effective permeability of formation crude oil, in mD; μ o is the viscosity of the formation crude oil, in mPa·s; M and N are coefficients and are dimensionless.

8. The method for determining the breakthrough pressure difference limit of top and bottom water invasion in a steam-throwing heavy oil reservoir according to claim 1, characterized in that: The specific method for determining the breakthrough pressure difference limit of the top and bottom water heavy oil reservoir in step S7 is: Based on the formation crude oil start-up pressure gradient distribution determined in step S6, the breakthrough pressure difference limits of top water and bottom water are calculated respectively; The calculation formula for the breakthrough pressure difference limit of top water is: The calculation formula for the breakthrough pressure difference limit of bottom water is: In formula (8) and (9): ΔP u is the limit of the top water breakthrough pressure difference, in MPa; r is the distance from each position to the horizontal well in the integral calculation, in m; r f is the wellbore radius, in m; r u is the distance between the horizontal well and the top water, in m; ρ o is the density of crude oil, in kg / m 3 ; ΔP l is the bottom water breakthrough pressure difference limit, in MPa; r l is the distance between the horizontal well and the bottom water, in meters; G o is the starting pressure gradient of the formation crude oil, in MPa / m; g represents the acceleration of gravity, in m / s 2 ; The breakthrough pressure difference limit of the top and bottom water is the minimum value min (ΔP u , ΔP l ).

Images