A method for predicting the optimal production of a low permeability reservoir

Abstract

The application discloses a kind of low-permeability reservoir's optimal production prediction method, considering starting pressure gradient and pressure sensitivity effect, including measuring the conventional parameter of reservoir;Carry out low-permeability core starting pressure gradient experiment, obtain starting pressure gradient and the relationship of permeability;Carry out low-permeability core stress sensitivity reservoir damage experiment, obtain the relationship of permeability and pressure difference;Get the production calculation model of low-permeability reservoir considering variable starting pressure gradient and pressure sensitivity effect;Draw the relationship curve of production and bottom hole flowing pressure, obtain the maximum of production.Determine optimal production, constant-pressure production, ensure that oil layer is less sensitive to pressure damage, improve the production of low-permeability reservoir, improve the development effect of low-permeability reservoir.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas field development technology, and in particular relates to an optimal production prediction method for low-permeability reservoirs considering the start-up pressure gradient and pressure sensitivity effect. Background Technology

[0002] In my country, a penetration rate of less than 50×10 is typically considered... -3 μm 2 Oil reservoirs with low permeability are called low-permeability reservoirs. Dagang Oilfield has developed geological reserves of 202 million tons of low-permeability reservoirs. Development began in 1971, primarily focusing on conventional low-permeability reservoirs, and in 2010, efforts began to tackle the development of ultra-low permeability reservoirs. Currently, the overall development effect of low-permeability reservoirs is not ideal, especially those with permeability less than 20 millidarcy, where oil production rates are low, recovery rates are low, water wells are under-injected or unable to inject water, and oil wells cannot produce any oil, resulting in poor development outcomes.

[0003] Long-term development practice and research have shown that low-permeability reservoirs have low permeability, narrow throats, and exhibit starting pressure gradients and stress sensitivity. Oil well production increases with increasing production pressure differential, reaching a maximum after a certain pressure differential, and then decreasing with further increases in pressure differential. Due to insufficient early understanding, production was often based on experience, leading to excessively high production pressure differentials, resulting in decreased reservoir permeability, insufficient or no water injection, poor reservoir energy retention, and a long-term vicious cycle of production without injection. This leads to increasingly lower well production, irreversible damage to reservoir properties, and ultimately, unsatisfactory development results. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide an optimal production prediction method for low-permeability reservoirs. This method considers the initiation pressure gradient and pressure-sensitive effect to find the optimal production pressure differential, thereby achieving constant pressure production. Establishing a reasonable production pressure differential increases well production, improves the development effect of low-permeability reservoirs, and enhances the overall benefits of reservoir development.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: an optimal production prediction method for low-permeability reservoirs, considering the initiation pressure gradient and pressure-sensitive effect, including the following steps:

[0006] Step 1: Measure the reservoir's conventional parameters, including initial permeability k. o The equivalent supply radius r under the oil layer thickness h and well pattern density e Original reservoir pressure p e Formation crude oil viscosity μ, water well injection pressure p o ;

[0007] Step 2: Conduct a low-permeability core start-up pressure gradient experiment to obtain the relationship between the start-up pressure gradient and permeability:

[0008] λ=ak -1

[0009] In the formula, λ is the pressure gradient, MPa / m; k is the permeability, mD; and a is a constant.

[0010] Step 3: Conduct stress-sensitive reservoir damage experiments using low-permeability core samples to obtain the relationship between permeability and pressure difference.

[0011]

[0012] In the formula, k is the permeability, mD; o Let mD be the initial permeability; p be the value of the initial permeability. s For supply pressure, MPa; p wf ρ is the bottom hole flowing pressure, MPa; ρ is a constant.

[0013] Step 4: Substitute the data obtained in Steps 1-3 into a production calculation model suitable for low-permeability reservoirs that considers variable start-up pressure gradients and pressure-sensitive effects.

[0014]

[0015] In the formula, q represents the output under the production pressure differential, and m 3 / d;p s For supply pressure, MPa; p wf λ is the bottomhole flowing pressure, MPa; μ is the formation crude oil viscosity, mPa / s; k is the permeability, mD; λ is the pressure gradient, MPa / m; h is the oil layer thickness, m; r e For the supply radius, m; r w Let be the radius of the wellbore, in meters (m).

[0016] Among them, supply pressure p s Calculated according to oilfield empirical formula

[0017] p s =p e +0.6p o

[0018] In the formula, p s For supply pressure, MPa; p e The original reservoir pressure is given in MPa; p o The water injection pressure for the water well is measured in MPa.

[0019] Step 5: Based on the production formula in Step 4, plot the relationship curve between production and bottom hole flowing pressure, and calculate the maximum production value.

[0020] The beneficial effects of this invention are: considering the starting pressure gradient and pressure-sensitive effect, finding the production pressure difference with the maximum production value, ensuring maximum production, minimizing pressure-sensitive damage to the oil reservoir, and thus maintaining constant pressure production, improving the production of low-permeability oil reservoirs, and enhancing the reservoir development effect. Attached Figure Description

[0021] Figure 1 A schematic diagram showing the relationship between production output and production pressure differential, taking into account the starting pressure and stress sensitivity of this invention.

[0022] Figure 2 A schematic diagram illustrating the relationship between the starting pressure gradient and permeability is provided for embodiments of the present invention;

[0023] Figure 3 A schematic diagram illustrating the relationship between pressure and permeability is provided for embodiments of the present invention;

[0024] Figure 4 The curve showing the relationship between production volume and dynamic liquid level is provided for an embodiment of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0026] The present invention provides an optimal production prediction method for low-permeability reservoirs, considering the initiation pressure gradient and pressure-sensitive effect, comprising the following steps:

[0027] Step 1: Measure the reservoir's conventional parameters, including initial permeability k. o The equivalent supply radius r under the oil layer thickness h and well pattern density e Original reservoir pressure p e Formation crude oil viscosity μ, water well injection pressure p o ;

[0028] Step 2: Conduct a low-permeability core start-up pressure gradient experiment to obtain the relationship between the start-up pressure gradient and permeability:

[0029] λ=ak -1

[0030] In the formula, λ is the pressure gradient, MPa / m; k is the permeability, mD; and a is a constant.

[0031] Step 3: Conduct stress-sensitive reservoir damage experiments using low-permeability core samples to obtain the relationship between permeability and pressure difference.

[0032]

[0033] In the formula, k is the permeability, mD; o Let mD be the initial permeability; p be the value of the initial permeability. s For supply pressure, MPa; p wf ρ is the bottom hole flowing pressure, MPa; ρ is a constant.

[0034] Step 4: Substitute the data obtained in Steps 1-3 into a production calculation model suitable for low-permeability reservoirs that considers variable start-up pressure gradients and pressure-sensitive effects.

[0035]

[0036] In the formula, q represents the output under the production pressure differential, and m 3 / d;p s For supply pressure, MPa; p wf λ is the bottomhole flowing pressure, MPa; μ is the formation crude oil viscosity, mPa / s; k is the permeability, mD; λ is the pressure gradient, MPa / m; h is the oil layer thickness, m; r e For the supply radius, m; r w Let be the radius of the wellbore, in meters (m).

[0037] Among them, supply pressure p s Calculated according to oilfield empirical formula

[0038] p s =p e +0.6p o

[0039] In the formula, p s For supply pressure, MPa; p e The original reservoir pressure is given in MPa; p o The water injection pressure for the water well is measured in MPa.

[0040] Step 5: Based on the production formula in Step 4, plot the production rate versus bottom hole flowing pressure curve, and calculate the maximum production rate. (See...) Figure 1 .

[0041] To make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings.

[0042] Based on a certain oilfield block in Dagang with a burial depth of 3000m, rock samples were obtained by core sampling from exploratory wells for research and testing.

[0043] In step 1, conventional parameters of the reservoir are measured, including the initial permeability k. o The equivalent supply radius r is 10mD, with an oil layer thickness h of 20m and a well pattern density. e 250m, wellbore radius r wThe depth is 0.127m, the viscosity of the formation crude oil is 2.5 mPa·s, and the original reservoir pressure is p. e For 30MPa, water well injection oil pressure p o It is 25 MPa.

[0044] In step 2, a low-permeability core initiation pressure gradient experiment was conducted to obtain the relationship between the initiation pressure gradient and permeability (see...). Figure 2 )

[0045] λ=0.127k -1

[0046] In step 3, a low-permeability core stress-sensitive reservoir damage experiment was conducted to obtain the relationship between permeability and pressure difference (see...). Figure 3 )

[0047]

[0048] In step 4, the starting pressure gradient function and permeability function are substituted into the production formula:

[0049]

[0050] In step 5, the permeability, starting pressure gradient, and production rate under different pressures are calculated and shown in Table 1. The relationship curve between production rate and dynamic liquid level is shown in Figure 5. Figure 4 As shown in the chart, the maximum daily production of the oil well is 4.03 tons when the dynamic fluid level is 1400m. The chart also shows that when the dynamic fluid level is greater than 1000m, the increase in production is smaller with increasing pressure differential. Therefore, maintaining a low production pressure differential can reduce stress-sensitive damage and achieve optimal production. In practice, a constant pressure production setting of 1000m dynamic fluid level, 300m submersion, and 1300m pump depth is sufficient for this constant pressure production.

[0051] Table 1

[0052]

[0053]

[0054] In summary, the content of this invention is not limited to the above-described embodiments. Those skilled in the art can easily propose other embodiments within the technical guiding principles of this invention, but such embodiments are all included within the scope of this invention.

Claims

1. A method for predicting the optimal production of a low permeability reservoir, characterized in that, Consider initiating the pressure gradient and pressure-sensitive effect, including the following steps: Step 1, measuring the conventional parameters of the reservoir, including initial permeability k o , oil layer thickness h, equivalent supply radius r under well pattern density e , original reservoir pressure p e , formation crude oil viscosity μ, water well injection oil pressure p o ; Step 2: Conduct a low-permeability core start-up pressure gradient experiment to obtain the relationship between the start-up pressure gradient and permeability: λ = ak -1 In the formula, λ is the pressure gradient, MPa / m; k is the permeability, mD; and a is a constant. Step 3: Conduct stress-sensitive reservoir damage experiments using low-permeability core samples to obtain the relationship between permeability and pressure difference. In the formula, k is the permeability, mD; k o Let mD be the initial permeability; p be the value of the initial permeability. s For supply pressure, MPa; p wf ρ is the bottom hole flowing pressure, MPa; b is a constant. Step 4: Substitute the data obtained in Steps 1-3 into a production calculation model suitable for low-permeability reservoirs that considers variable start-up pressure gradients and pressure-sensitive effects. In the formula, q represents the output under the production pressure differential, and m 3 / d;p s For supply pressure, MPa; p wf λ is the bottomhole flowing pressure, MPa; μ is the formation crude oil viscosity, mPa / s; k is the permeability, mD; λ is the pressure gradient, MPa / m; h is the oil layer thickness, m; r e For the supply radius, m; r w Let be the radius of the wellbore, in meters (m). wherein the supply pressure p s According to the oil field empirical formula p s = p e + 0.6p o where p s is the supply pressure, MPa; p e is the original reservoir pressure, MPa; p o is the water injection pressure, MPa; Step 5: Based on the production formula in Step 4, plot the relationship curve between production and bottom hole flowing pressure, and calculate the maximum production value.

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