A method for predicting formation pressure during tight oil steam flooding with expansion enhancement

Abstract

The invention provides a method for predicting formation pressure of tight oil steam drive expansion energy enhancement, comprising the following steps: step 1, calculating the expansion coefficient and compression coefficient of the crude oil in the tight oil reservoir at different temperatures; step 2, calculating the average oil saturation of the crude oil in the tight oil reservoir; step 3, calculating the steam drive expansion energy enhancement formation pressure of the tight oil reservoir at different steam temperatures considering different fluid saturations according to the results of step 1 and step 2; the method only requires basic physical parameters such as the compression coefficient, expansion coefficient, steam temperature and water saturation of the crude oil and formation water at different reservoir pressure temperatures, and uses the established theoretical calculation formula to achieve accurate prediction of the formation pressure, thereby providing a basis for the design of key parameters such as the temperature, velocity and dryness of the steam injected on the ground.

Description

Technical Field

[0001] The invention relates to the technical field of improving oil recovery in oil and gas field development, and in particular to a method for predicting tight oil steam drive expansion energy enhancement formation pressure. Background Art

[0002] Tight oil refers to oil stored in tight sandstone, tight carbonate and other reservoirs with effective permeability less than or equal to 0.1mD. In a broad sense, tight oil refers to oil produced in low-porosity and low-permeability shale or other tight rock reservoirs. As an important type of unconventional oil reservoir, tight oil has low reservoir permeability, which makes it difficult to establish an effective displacement pressure system by water injection under the economic limit well network. At present, the "horizontal well + volume fracturing" method is usually adopted for quasi-natural energy development. Since the formation energy cannot be effectively supplemented, the production decline in the tight oil development process is large, and the recovery rate is much lower than that of conventional water injection development reservoirs, which is only about 10%.

[0003] Steam flooding improves oil recovery by reducing viscosity, distilling, and thermal expansion. Both practice and theory have proven that steam flooding is an effective way to develop heavy oil, among which viscosity reduction is the most important mechanism for steam flooding heavy oil. Tight oil reservoirs are generally light crude oils with good thermal expansion properties. By utilizing the thermal expansion properties of light crude oils, it is possible to increase formation energy by expanding the crude oil volume after steam heating. Accurately predicting the formation pressure of steam flooding in tight oil reservoirs is the key to steam flooding energy replenishment, which directly determines the design of key parameters such as surface injection steam temperature, velocity, and dryness.

[0004] At present, there is no report on the prediction method of tight oil steam flooding expansion energy enhancement formation pressure. Therefore, the compression coefficient and expansion coefficient of crude oil and formation water at different temperatures are calculated by numerical simulation, and the expansion energy enhancement calculation formula under different reservoir steam temperatures and different water saturations is established to predict the increase degree of tight oil steam flooding expansion energy enhancement formation pressure. Summary of the invention

[0005] The purpose of the present invention is to provide a method for predicting formation pressure during tight oil steam flooding expansion and energization, which solves the shortcomings of the prior art.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] The present invention provides a method for predicting formation pressure during tight oil steam flooding expansion and energization, comprising the following steps:

[0008] Step 1, calculating the expansion coefficient and compression coefficient of the crude oil in the tight oil reservoir at different temperatures;

[0009] Step 2, calculating the average oil saturation of the crude oil in the tight oil reservoir;

[0010] Step 3, based on the results of Step 1 and Step 2, calculate the steam expansion energization formation pressure of the tight oil reservoir at different steam temperatures considering different fluid saturations.

[0011] Preferably, in step 1, the expansion coefficient and the compression coefficient of the crude oil in the tight oil reservoir at different temperatures are calculated by:

[0012] The expansion coefficient and compression coefficient of crude oil in tight oil reservoirs at different temperatures are calculated using numerical simulation method.

[0013] Preferably, in step 2, the average oil saturation of the crude oil in the tight oil reservoir is calculated by:

[0014] Closed coring is performed on different coring wells and rock samples from different parts of the tight oil reservoir block to test the original oil saturation of rock samples from different coring wells and different parts;

[0015] The average oil saturation of rock samples from different coring wells and different locations is calculated and taken as the average oil saturation of the tight oil reservoir block.

[0016] Preferably, in step 3, the steam flooding expansion energization formation pressure of the tight oil reservoir under different steam temperatures with different fluid saturations is calculated by:

[0017]

[0018] Among them, α o is the expansion coefficient of crude oil, 1 / ℃; C o is the compressibility of crude oil, 1 / MPa; T i is the original reservoir temperature; T is the temperature of crude oil after expansion, ℃; P is the formation pressure after crude oil expansion; P i is the formation pressure before steam injection; S w is the water saturation.

[0019] Preferably, the water saturation S w Calculated by the following formula:

[0020] S w =1-S o

[0021] Among them, S o is the average oil saturation of the crude oil in the tight oil reservoir calculated in step 2.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] The present invention provides a method for predicting formation pressure by expansion energy enhancement of tight oil steam drive. The method uses numerical simulation software to calculate the expansion coefficient and compression coefficient of crude oil and formation water at different temperatures, establishes a theoretical calculation formula for expansion energy enhancement, and calculates the formation pressure under different steam temperatures and fluid saturations. The method only requires basic physical parameters such as the compression coefficient, expansion coefficient, steam temperature and water saturation of crude oil and formation water at different reservoir pressure temperatures. The established theoretical calculation formula is used to achieve accurate prediction of formation pressure, providing a basis for the design of key parameters such as ground injection steam temperature, velocity and dryness. DETAILED DESCRIPTION

[0024] The present invention is described in further detail below.

[0025] The present invention provides a method for predicting formation pressure of tight oil steam drive expansion energy enhancement, which is based on clarifying the theoretical calculation formula of steam drive expansion energy enhancement, and establishes a method for predicting formation pressure of tight oil steam drive expansion energy enhancement with four parameters of crude oil expansion coefficient, compression coefficient, oil saturation and steam temperature. First, establish expansion energy enhancement calculation formulas for different temperatures and oil saturations; second, obtain the expansion coefficient and compression coefficient of crude oil at different temperatures of reservoir pressure through numerical simulation phase calculation tools; third, obtain oil saturation based on the statistical results of closed coring analysis of tight oil blocks; fourth, calculate the formation pressure of tight oil reservoirs at different steam temperatures. The specific process is as follows:

[0026] The calculation formula of formation pressure under different steam temperatures in tight oil reservoirs considering different fluid saturations is established. Specifically:

[0027] Based on the definition formula of expansion coefficient and compression coefficient, the relationship between temperature and pressure is established.

[0028] The expansion coefficient is the rate of change of fluid volume per unit temperature change. Based on the definition of the expansion coefficient, the relationship between temperature change and volume change can be established, as shown in formula (1):

[0029]

[0030] The compressibility coefficient is the rate of change of fluid volume under unit pressure change. According to the definition of compressibility coefficient, the relationship between pressure change and volume change can be established, as shown in formula (2):

[0031]

[0032] According to formula (1) and formula (2), the relationship between temperature change and pressure change is established, and the calculation of formation pressure change caused by crude oil expansion at different temperatures is obtained, such as formula (3):

[0033]

[0034] Since there is not only oil in the pores of the formation, but also oil and water coexist, when the water saturation in the formation is considered, formula (3) becomes formula (4):

[0035]

[0036] Since the compressibility coefficient of water is C w (Order of magnitude 10 -2 1 / MPa) than the compression coefficient C of light crude oil o (10 -4 1 / MPa) is two orders of magnitude higher, that is, the elastic energy increase amplitude of water is much smaller than that of oil, so formula (4) can be simplified to formula (5):

[0037]

[0038] Therefore, the calculation formula of steam flooding expansion energy enhancement formation pressure can be obtained as follows (6):

[0039]

[0040] In the above formula: α o and α w are the expansion coefficients of crude oil and formation water, 1 / ℃; C o and C w are the compression coefficients of crude oil and formation water, 1 / MPa; ΔV is the volume change of crude oil due to thermal expansion; V is the initial volume of crude oil, mL; ΔT is the temperature change; T i is the original reservoir temperature; T is the temperature of crude oil after expansion, ℃; P is the formation pressure after crude oil expansion; P i is the formation pressure before steam injection; ΔP is the change in crude oil pressure, MPa; S w is water saturation; S o is the oil saturation.

[0041] According to the theoretical calculation formula of steam flooding expansion energy enhancement formation pressure, the formation pressure after steam flooding is related to steam temperature, oil saturation, formation crude oil compression coefficient, expansion coefficient and formation pressure before steam injection. Among them, the temperature of the reservoir and the formation pressure before steam flooding are relatively easy to obtain, while the expansion coefficient, compression coefficient and oil saturation are difficult to obtain.

[0042] Therefore, the present invention provides a method for predicting tight oil steam flooding expansion energization formation pressure, which specifically includes the following steps:

[0043] Step 1: Calculate the expansion coefficient and compression coefficient of crude oil in tight oil reservoirs at different temperatures using numerical simulation method. The specific process is as follows:

[0044] 1) Testing the total hydrocarbon components of formation crude oil by gas chromatography;

[0045] 2) Use reservoir numerical simulation phase calculation tools to split crude oil components;

[0046] 3) Perform phase calculations on pseudo-component crude oil, fit physical parameters such as saturation pressure, density and gas-oil ratio at reservoir temperature, and clarify the characteristic parameters of pseudo-components, including critical temperature, critical pressure, binary interaction coefficient, etc.;

[0047] 4) The heating expansion simulation calculation is carried out on the pseudo-component crude oil with determined characteristic parameters. The temperature is increased by 10°C / time starting from the original reservoir temperature until the temperature reaches 300°C, and the expansion coefficient and compression coefficient of the crude oil at different temperatures are obtained.

[0048] Step 2: Calculate the average oil saturation based on the tight coring test results of the tight oil reservoir. Specifically:

[0049] According to the petroleum and natural gas industry standard SY / T 5366-2000 "Technical Requirements for Coring Data of Oilfield Development Wells", the tight oil block was cored to test the original oil saturation. The average oil saturation of rock samples from different parts of different coring wells represents the average oil saturation S of the tight oil block. o , calculate water saturation S based on oil saturation w , the calculation formula is as follows formula (7):

[0050] S w =1-S o (7)

[0051] Step 3, calculate the formation pressure of steam flooding expansion energy enhancement at different steam temperatures, specifically:

[0052] According to the expansion coefficient and compression coefficient determined in step 2 and the average oil saturation of the block measured in step 3, they are substituted into formula (6) to calculate the formation pressure of steam flooding expansion energy enhancement at different steam temperatures. According to the actual steam formation temperature, the actual formation pressure is calculated.

[0053] The present invention is based on the theoretical calculation formula of steam drive expansion energy enhancement, and establishes a method for predicting the formation pressure of tight oil steam drive expansion energy enhancement by using four parameters of crude oil expansion coefficient, compression coefficient, oil saturation and steam temperature. Numerical simulation software is used to calculate the expansion coefficient and compression coefficient of crude oil and formation water at different temperatures, and the average oil saturation is calculated based on the results of tight oil reservoir closed coring test. This method only requires basic physical parameters such as compression coefficient, expansion coefficient, steam temperature and water saturation of crude oil and formation water at different temperatures of reservoir pressure to achieve accurate prediction of formation pressure, and provide a basis for the design of key parameters such as ground injection steam temperature, velocity and dryness.

[0054] At present, there are no reports on the method of predicting the formation pressure of tight oil steam flooding expansion energy enhancement, mainly because steam flooding is usually used in heavy oil reservoirs, and tight oil, as a typical representative of unconventional resources, is mainly characterized by a high content of light components in crude oil and good fluidity, and the mindset of steam flooding has not been broken.

Claims

1. A method for predicting formation pressure during tight oil steam flooding expansion and energy enhancement, characterized in that: The following steps are involved: Step 1, calculating the expansion coefficient and compression coefficient of the crude oil in the tight oil reservoir at different temperatures; Step 2, calculating the average oil saturation of the crude oil in the tight oil reservoir; Step 3, based on the results obtained in Step 1 and Step 2, calculate the steam flooding expansion energization formation pressure at different steam temperatures in the tight oil reservoir considering different fluid saturations; In step 3, the steam expansion energization formation pressure of the tight oil reservoir under different steam temperatures with different fluid saturations is calculated. The specific method is: Among them, α o is the expansion coefficient of crude oil, 1 / ℃; C o is the compressibility of crude oil, 1 / MPa; T i is the original reservoir temperature; T is the temperature of crude oil after expansion, ℃; P is the formation pressure after crude oil expansion; P i is the formation pressure before steam injection; S w is the water saturation.

2. A method for predicting formation pressure by expansion and energization of tight oil steam flooding according to claim 1, characterized in that: In step 1, the expansion coefficient and compression coefficient of the crude oil in the tight oil reservoir at different temperatures are calculated by: The expansion coefficient and compression coefficient of crude oil in tight oil reservoirs at different temperatures are calculated using numerical simulation method.

3. A method for predicting formation pressure by expansion and energization of tight oil steam flooding according to claim 1, characterized in that: In step 2, the average oil saturation of crude oil in tight oil reservoirs is calculated by: Closed coring is performed on different coring wells and rock samples from different parts of the tight oil reservoir block to test the original oil saturation of rock samples from different coring wells and different parts; The average oil saturation of rock samples from different coring wells and different locations is calculated and taken as the average oil saturation of the tight oil reservoir block.

4. A method for predicting formation pressure by expansion and energization of tight oil steam flooding according to claim 1, characterized in that: The water saturation S w Calculated by the following formula: S w =1-S o Among them, S o is the average oil saturation of the crude oil in the tight oil reservoir calculated in step 2.

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