A design method of steam injection parameter in steam stimulation oil production

Abstract

The present application relates to a kind of steam injection parameter design method in steam huff and puff oil production, belong to oil well exploitation technical field.The steam injection parameter design method in steam huff and puff oil production of the present application, superheated steam is used to carry out steam huff and puff to target reservoir, the injection amount of superheated steam is determined by calculation, with the advantages of simple operation, accurate result, can avoid the current steam injection parameter in steam huff and puff oil production cannot be quantitatively designed, thereby causing the problem of steam injection amount too much or insufficient.The steam injection parameter design method in steam huff and puff oil production of the present application, optimization space is larger, after investigation in many aspects, based on original steam distribution method, combined with formation condition, steam parameter and different huff and puff cycle, by theoretical analysis, deduce steam injection parameter design method based on heat energy overall balance, steam injection parameter can be quantitatively designed to a certain extent.

Description

Technical Field

[0001] This invention relates to a method for designing steam injection parameters in steam huff and puff oil production, belonging to the field of oil well development technology. Background Technology

[0002] Currently, steam injection is commonly used for the extraction of heavy oil reservoirs. In this method, each steam injection cycle consists of three stages: steam injection, well shut-in, and production. During the steam injection stage, high-temperature steam is injected into the oil layer, typically for several days to over ten days. After steam injection stops, the well shut-in stage begins, where the well is closed to allow for sufficient heat exchange between the steam and the reservoir fluids. After well shut-in, the production stage begins, and the well is opened for oil extraction. As time progresses and production continues, the temperature of the steam-heated formation gradually decreases, the viscosity of the heavy oil increases, and the oil recovery rate and daily production gradually decline from the peak production at the time of well opening. To improve the recovery rate, the next steam injection cycle is required. After multiple rounds of steam injection, steam and water channeling develops, thermal energy utilization decreases, and the oilfield needs to reduce extraction costs in various aspects. In heavy oil thermal recovery, the amount of steam injected and the cost of steam account for a large proportion. Currently, when steam huff and puff is used for oil recovery, the amount of steam injected is usually 120 tons per meter of oil layer thickness. The steam volume designed for different steam huff and puff cycles is equal to 120 × H × (1 + 15%). n-1 When the steam injection cycle is no more than 5, n = steam injection cycle; when the steam injection cycle is greater than 5, n = 5, and H is the oil layer thickness. This method is the traditional steam injection parameter design method. However, the steam quantity calculated by this method has a large error, resulting in high production costs.

[0003] In order to reduce production costs, there is an urgent need to develop a design method for steam injection parameters in steam huff and puff oil production. Summary of the Invention

[0004] The purpose of this invention is to provide a design method for steam injection parameters in steam huff and puff oil recovery, which can solve the problem that the current steam injection parameters in steam huff and puff oil recovery cannot be quantitatively designed, resulting in excessive or insufficient steam injection.

[0005] To achieve the above objectives, the technical solution adopted in the steam injection parameter design method for steam huff and puff oil recovery of the present invention is as follows:

[0006] A method for designing steam injection parameters in steam huff and puff oil recovery includes the following steps: steam is used to perform steam huff and puff on the target reservoir, wherein the steam is superheated steam, saturated steam, or wet steam, and the steam injection rate is calculated using the following formula:

[0007]

[0008] In the formula, M 汽 The mass of steam is represented by T, k is a correction factor, and T is the mass of steam. 原始 T represents the original formation temperature. 目标 Indicates the target temperature, C 油 M represents the specific heat capacity of the underground crude oil in the target reservoir. 油 C represents the mass of underground crude oil within the steam field's reach. 水1 M represents the specific heat capacity of formation water in the target oil reservoir. 水 C represents the mass of formation water within the steam-bearing area. 岩石 M represents the specific heat capacity of the rock framework in the target reservoir. 岩石 C represents the mass of the rock framework within the steam-borne range. 汽 T represents the specific heat capacity of steam. 汽 T represents the temperature of the steam. 饱和 C represents the temperature of saturated vapor at a depth within the target oil reservoir under formation pressure conditions. 水2 L represents the specific heat capacity of saturated water under formation pressure conditions at a depth in the middle of the target oil reservoir. v This represents the heat released when steam condenses into saturated water under formation pressure conditions at the middle depth of the target oil reservoir, where n is a parameter related to the steam huff and puff cycle.

[0009] The steam injection parameter design method for steam huff and puff oil recovery of this invention uses superheated steam to perform steam huff and puff on the target reservoir. The injection volume of superheated steam is determined by calculation, offering advantages such as simple operation and accurate results. This avoids the problem of excessive or insufficient steam injection caused by the inability to quantitatively design steam injection parameters in current steam huff and puff oil recovery methods. The steam injection parameter design method of this invention has significant optimization potential. Based on extensive research and existing steam distribution methods, and considering different formation conditions, steam parameters, and huff and puff cycles, a steam injection parameter design method based on overall thermal energy balance is derived through theoretical analysis. This method allows for quantitative design of steam injection parameters to a certain extent.

[0010] Saturation temperature refers to the temperature at which liquid water and vapor water are in a two-phase equilibrium state, i.e., a saturated state. At this point, the temperatures of the liquid water and the vapor are equal. The saturation temperature of a substance corresponds to its saturation pressure. After water reaches its saturation temperature, if heating is carried out under constant pressure, the saturated water vaporizes. Before the water is completely vaporized, the steam containing saturated water is called wet saturated steam, or simply wet steam. Steam dryness fraction refers to the percentage of saturated dry steam per kilogram of wet steam. From the process of heating liquid water to form saturated steam, liquid water is heated under a certain pressure, absorbs heat (sensible heat), and its temperature rises, becoming saturated water. When saturated water continues to be heated, its temperature remains constant, but it absorbs heat (latent heat), changing from a liquid state to a gaseous state. When all the liquid water has vaporized, saturated steam (dry saturated steam) is formed. Figure 1 As shown.

[0011] For wet steam at a constant temperature but with a dryness fraction not equal to 1, an increase in pressure causes the wet steam to rapidly transform into hot water, while a decrease in pressure causes the dryness fraction of the wet steam to increase. If the pressure continues to decrease, the wet steam can transform into dry steam or even superheated steam. In the steam injection development process of heavy oil reservoirs, the dryness fraction of the steam at the bottom of the well is usually less than 1. The wet steam moves from the bottom of the well to the deeper oil layer, gradually releasing heat (latent heat of vaporization), and the dryness fraction decreases. When the latent heat carried by the steam injected into the formation per unit time is greater than the heat absorbed by the formation, wet steam will exist in the rock pores of local areas within the formation.

[0012] Enthalpy is a state function representing the energy of a substance. Taking air as an example, the enthalpy of air refers to the total heat contained in the air. It can be seen that the enthalpy of steam refers to the total heat contained in the steam. When steam is injected into the downhole oil reservoir, it heats the underground crude oil, formation water, and rock framework within its sphere of influence. Ideally, after steam is injected into the reservoir, it heats the underground crude oil, formation water, and rock framework from the near-wellbore area to the far-wellbore area. During this process, the steam temperature decreases, eventually becoming liquid water; the underground crude oil, formation water, and rock framework absorb heat, and their temperature increases. Theoretically, the heat exchange ends when the temperature of the cooled steam equals the temperature of the heated underground crude oil, formation water, and rock framework.

[0013] It is understandable that when the steam is superheated steam, T 汽 >T 饱和 When the steam is saturated steam or wet steam, T 汽 =T 饱和 .

[0014] To ensure the effectiveness of steam huff and puff oil recovery, preferably, the target reservoir is a heavy oil reservoir that meets the conditions for steam huff and puff development.

[0015] It is understood that the target temperature refers to the temperature at which underground crude oil is heated to a point where it can flow. Preferably, the target temperature is the temperature at which the viscosity of the underground crude oil in the target reservoir is not greater than 2000 mPa·s.

[0016] There are two methods to determine the original formation temperature: one is to use temperature and pressure measurement data, and the other is to use the temperature and pressure coefficient of the target reservoir and calculate the original formation temperature in combination with the middle depth of the oil layer.

[0017] To improve the accuracy of steam injection parameter design, heat loss needs to be considered. The calculated steam injection amount can be corrected according to the type of the target reservoir. Preferably, when the target reservoir is a shallow reservoir, k = 1.1 to 1.2; when the target reservoir is a water-edge reservoir, k = 1.25 to 1.3.

[0018] In this invention, a shallow reservoir refers to an oil reservoir with a burial depth of less than 800m and a thickness of less than 3m.

[0019] Preferably, when the steam huff and puff cycle is no greater than 5, n = the steam huff and puff cycle; when the steam huff and puff cycle is greater than 5, n = 5. For example, when the steam huff and puff cycle is the 1st cycle, n = 1; when the steam huff and puff cycle is the 6th cycle, n = 5. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process by which liquid water forms saturated steam (dry saturated steam) in this invention;

[0021] Figure 2 This is a schematic diagram of the latent heat of vaporization of saturated steam under different pressure conditions in an embodiment of the present invention.

[0022] Figure 3 This is a schematic diagram of the temperature of saturated steam under different pressure conditions in an embodiment of the present invention. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0024] Example

[0025] Taking steam huff and puff recovery of an oil reservoir in a certain area using superheated steam (dry saturated steam) as an example, the design method of steam injection parameters in steam huff and puff recovery in this embodiment specifically includes the following steps:

[0026] (1) Determination of the required heat value of the formation

[0027] After steam is injected into the formation, it exchanges heat with underground crude oil, formation water, and rock framework. Without considering heat loss, the underground crude oil, formation water, and rock framework are heated to a specific temperature point (target temperature, defined as T). 目标 The amount of heat (Q) required to absorb when ) 地层 The required heat value for the formation is shown in Equation 1.

[0028] Q 地层 =Q1+Q2+Q3 Equation 1

[0029] In Equation 1, Q1 represents the amount of heat required to heat the rock grid to the target temperature, in J.

[0030] Q2 represents the amount of heat required to heat the formation water to the target temperature, in J;

[0031] Q3 represents the amount of heat required to heat underground crude oil to the target temperature, in J;

[0032] The method for calculating the amount of heat required to heat a substance (medium) to a target temperature is shown in Equation 2:

[0033] Q = C × M × ΔT (Equation 2)

[0034] In Equation 2, Q represents the calorific value, in J;

[0035] M represents the mass of the corresponding medium, in kg;

[0036] C represents the specific heat capacity of the corresponding medium, with units of J / kg / ℃;

[0037] ΔT represents the temperature change of the corresponding medium (i.e., the difference between the target temperature and the original formation temperature), in °C.

[0038] The method for calculating the mass of a certain substance (medium) is shown in Equation 3:

[0039] M = ρ × V (Equation 3)

[0040] In Equation 3, ρ represents the density of the corresponding medium, with units of kg / m³. 3 ;

[0041] V represents the volume of the corresponding medium, in cubic meters (m³). 3 ;

[0042] In calculating the heat required for the formation, only three media are considered: formation water, rock grid and underground crude oil. Substituting Formula 2 and Formula 3 into Formula 1, the heat required for the formation during the steam injection process can be calculated.

[0043] (2) The amount of heat released by superheated steam

[0044] During steam injection, superheated steam is generally used. Steam is in a heat dissipation process. Without considering heat loss, the steam will become hot water at a certain temperature when the heat dissipation ends; this temperature is the target temperature. The steam heat dissipation process can be divided into three stages: superheated steam (dry saturated steam) transforms into wet saturated steam; wet saturated steam transforms into high-temperature liquid water (during which the temperature of the wet saturated steam remains constant and equals the temperature of the high-temperature liquid water); and high-temperature liquid water transforms into liquid water at the target temperature. The heat released by the steam in these three stages are ΔQ1, ΔQ2, and ΔQ3, respectively. If wet saturated steam is used, there is no process of superheated steam (dry saturated steam) transforming into wet saturated steam.

[0045] (3) Calculation formula for the steam distribution process

[0046] During the steam distribution calculation, the mass of steam can be calculated based on the fact that the heat value required by the formation is equal to the heat value released by the superheated steam.

[0047] When the heat required by the formation is equal to the heat released by the superheated steam, the heat released by the steam must satisfy Equation 4:

[0048] Q1+Q2+Q3=ΔQ1+X×ΔQ2+ΔQ3 Equation 4

[0049] In Equation 4, the sum of Q1+Q2+Q3 represents the amount of heat required to heat the formation to the target temperature (including the amount of heat required to heat the rock framework, formation water, and underground crude oil to the target temperature), ΔQ1 is the amount of heat released when superheated steam changes into wet saturated steam, ΔQ2 is the amount of heat released when wet saturated steam changes (liquefies) into high-temperature liquid water, ΔQ3 is the amount of heat released when high-temperature liquid water changes into liquid water at the target temperature, and X is the dryness of the wet saturated steam.

[0050] The mass of the superheated steam is calculated using Equation 5:

[0051]

[0052] In Equation 5, M 汽0 Indicates the mass of superheated steam;

[0053] T 原始 This indicates the original formation temperature, or the formation temperature before the injection of superheated steam, in °C.

[0054] T 目标 Indicates the target temperature, in °C;

[0055] C 油 This indicates the specific heat capacity of the underground crude oil in the target reservoir, expressed in J / kg / ℃.

[0056] C 水1 This indicates the specific heat capacity of formation water in the target reservoir, expressed in J / kg / ℃.

[0057] C 岩石 This indicates the specific heat capacity of the rock framework in the target reservoir, expressed in J / kg / ℃.

[0058] C 汽 This indicates the specific heat capacity of superheated steam, expressed in J / kg / ℃.

[0059] T 汽 This indicates the temperature of superheated steam, expressed in °C.

[0060] T 饱和 This indicates the temperature of saturated vapor under formation pressure conditions at the middle depth of the target oil reservoir, expressed in °C.

[0061] C 水2 This represents the specific heat capacity of saturated water under formation pressure conditions at the middle depth of the target oil reservoir, expressed in J / kg / ℃.

[0062] L v This represents the latent heat of vaporization, expressed in J.

[0063] M 油 This indicates the mass of underground crude oil within the steam wave's reach, expressed in kg.

[0064] M 水 This indicates the mass of formation water within the steam-bearing area, expressed in kg.

[0065] M 岩石 This indicates the mass of the rock lattice within the steam wave's reach, expressed in kg.

[0066] (4) Design of steam injection parameters

[0067] Based on the above results, the following parameters are necessary to calculate the mass of superheated steam:

[0068] ①Target temperature (T) 目标 )

[0069] The target temperature is the temperature that the formation needs to be heated to. This temperature is calculated primarily based on the viscosity-temperature curve of the steam injection well. Generally, it is considered that underground crude oil can flow when its viscosity is 2000 mPa·s. Therefore, the temperature corresponding to a crude oil viscosity of 2000 mPa·s is the minimum temperature that the crude oil, formation water, and rock skeleton need to reach, i.e., the target temperature T. 目标 ;

[0070] ②Original temperature (T) 原始 )

[0071] There are two methods to confirm the original temperature: one is to use temperature and pressure measurement data, and the other is to use the temperature and pressure coefficient of the region and calculate the original temperature in combination with the middle depth of the oil layer.

[0072] ③ Specific heat capacity, density, and volume of the corresponding medium

[0073] The specific heat capacity and density of the corresponding medium were obtained by consulting relevant literature. According to the literature, the density of the underground crude oil in this region is 800 kg / m³. 3 Its specific heat capacity is 3.0 kJ / kg / ℃, and the density of formation water is 1000 kg / m³. 3 Its specific heat capacity is 4.2 kJ / kg / ℃, and the density of the rock framework is 2800 kg / m³. 3 Its specific heat capacity is 0.8 kJ / kg / ℃;

[0074] The volume of the rock is calculated using the following formula: V = π × R 2 ×H, where R is the vapor radius (obtained through numerical simulation), and H is the rock thickness. In this embodiment, the vapor radius R is 35m, and the rock thickness H is 2m. The calculated rock volume V is 7963m³. 3 The total volume of formation water and underground crude oil is equal to the volume of pores in the rock. In this embodiment, the porosity of the rock is 30%, therefore, the total volume of formation water and underground crude oil is 2389 m³. 3 The original oil saturation was 65% and the water content was 35%, meaning the mass ratio of underground crude oil to formation water was 65:35. Based on the densities of underground crude oil and formation water, the volume ratio of underground crude oil to formation water can be calculated. Finally, based on the volume ratio of underground crude oil to formation water and the total volume of formation water and underground crude oil, the volumes of formation water and underground crude oil can be calculated separately.

[0075] ④ Saturation temperature and latent heat of vaporization of steam

[0076] The temperature of saturated steam under a certain pressure condition and the heat released during the liquefaction of dry steam in wet saturated steam (latent heat of vaporization) can be calculated by consulting literature, data, or by looking up enthalpy tables of steam under different states, or by using fitting formulas; the latent heat of vaporization of saturated steam under different pressure conditions is as follows: Figure 2 As shown, Figure 2 The horizontal axis represents pressure in MPa, and the vertical axis represents latent heat of vaporization in J; the temperature of saturated steam under different pressure conditions is shown in the figure. Figure 3 As shown, Figure 3 The horizontal axis represents pressure, in MPa, and the vertical axis represents temperature, in °C.

[0077] To improve the accuracy of steam injection parameter design, heat loss needs to be considered. The calculated steam injection rate can be corrected according to the type of the target reservoir. For shallow reservoirs, the corrected steam injection rate is equal to k×M. 汽 k = 1.1~1.2; for edge water reservoirs, the corrected steam injection rate is equal to k × M 汽0 k = 1.25 to 1.3.

[0078] To improve the steam injection efficiency, the impact of the steam injection cycle on the calculated steam volume needs to be considered. Therefore, the final formula for calculating the steam injection volume is as follows:

[0079]

[0080] In the formula, M 汽 The mass of steam is represented by T, k is a correction factor, and T is the mass of steam. 原始 T represents the original formation temperature. 目标 Indicates the target temperature, C 油 M represents the specific heat capacity of the underground crude oil in the target reservoir. 油 C represents the mass of underground crude oil within the steam field's reach. 水1 M represents the specific heat capacity of formation water in the target oil reservoir. 水 C represents the mass of formation water within the steam-bearing area. 岩石 M represents the specific heat capacity of the rock framework in the target reservoir. 岩石 C represents the mass of the rock framework within the steam-borne range. 汽 T represents the specific heat capacity of steam. 汽 T represents the temperature of the steam. 饱和 C represents the temperature of saturated vapor at a depth within the target oil reservoir under formation pressure conditions. 水2 L represents the specific heat capacity of saturated water under formation pressure conditions at a depth in the middle of the target oil reservoir. v This represents the heat released when steam condenses into saturated water under formation pressure conditions at the middle depth of the target reservoir's oil layer. n is a parameter related to the steam huff and puff cycle. When the target reservoir is a shallow reservoir, k = 1.1 to 1.2; when the target reservoir is a water-edge reservoir, k = 1.25 to 1.3; when the steam huff and puff cycle is not greater than 5, n = steam huff and puff cycle; when the steam huff and puff cycle is greater than 5, n = 5.

[0081] Experimental Example

[0082] Taking a new well (a shallow oil reservoir) as an example, the original formation temperature is 31.3℃, the viscosity of the underground crude oil is 8569.5 mPa·s, and the target temperature is 50℃. Therefore, the temperature of the formation water, rock grid, and underground crude oil needs to be increased by 18.7℃, and the steam injection dryness is 75%. In order to compare the steam injection parameter design method of the present invention with the traditional steam injection parameter design method, firstly, the steam injection amount required for the third cycle of steam huff and puff is calculated to be 795t according to the traditional steam injection parameter design method. Then, the steam injection amount required for the fourth cycle of steam huff and puff is calculated to be 486t according to the steam injection parameter design method of the present invention (k=1.1 is used when correcting the calculated steam injection amount). Then, the steam huff and puff operation is carried out according to the calculated steam injection amount. At the same time, the production time, cumulative liquid production, cumulative oil production, and daily oil production after steam huff and puff are summarized in Table 1.

[0083] Table 1. Production effect of a certain production layer (H3Ⅲ2) of a certain new well at different stages.

[0084]

[0085] The cycle benefit comparison calculation is as follows:

[0086] Crude oil is calculated at $50 (2220 yuan), and steam at 157 yuan:

[0087] Comparison of effects over time:

[0088] Third cycle: Total investment = 795×157 + 202×20 + 1452.8×9.7 + 1452.8×7.3 = 154,000 yuan, Revenue = 639.6×2220 = 1,419,000 yuan, Benefit = 1,419,000 - 154,000 = 1,265,000 yuan, Input-output ratio is 1:9.2; Wherein, 795×157 represents steam cost input, 202×20 represents material cost input, 1452.8×9.7 represents liquid treatment cost input, and 1452.8×7.3 represents electricity cost input;

[0089] Fourth cycle: Total investment = 486×157 + 162.5×20 + 895.9×9.7 + 895.9×7.3 = 95,000 yuan, Revenue = 5,245×2220 = 1,164,000 yuan, Benefit = 1,164,000 - 95,000 = 1,069,000 yuan, Input-output ratio is 1:12.3; Wherein, 486×157 represents steam cost input, 162.5×20 represents material cost input, 895.9×9.7 represents liquid treatment cost input, and 895.9×7.3 represents electricity cost input;

[0090] Comparison of cycle benefits:

[0091] Steam distribution benefits in the third cycle: Operating cost per ton of oil = 127.1 + (157 × 795) / (639.6 × 0.82 × 0.8981) = 392.1 yuan / ton, where 127.1 represents the operating cost per ton of oil, 0.82 represents the tank loading rate, and 0.8981 represents the commodity rate;

[0092] Steam distribution benefits in the 4th cycle: Operating cost per ton of oil = 127.1 + (157 × 486) / (524.5 × 0.82 × 0.8981) = 324.6 yuan / ton, where 127.1 represents the operating cost per ton of oil, 0.82 represents the tank loading rate, and 0.8981 represents the commodity rate;

[0093] From a cyclical perspective, the steam distribution benefit in the third cycle was 1.265 million yuan, with an input-output ratio of 1:9.2, and the benefit in the fourth cycle was 1.069 million yuan, with an input-output ratio of 1:12.3. In terms of efficiency, the operating cost per ton of oil was 392.1 yuan in the third cycle and 324.6 yuan in the fourth cycle, representing a reduction of 67.5 yuan per ton of oil. Therefore, when steam distribution is carried out using the parameters designed by the steam injection parameter design method in steam huff and puff oil production of this invention, it has a certain improvement effect on both production efficiency and economic benefits.

Claims

1. A method for designing steam injection parameters in steam huff and puff oil recovery, characterized in that, The process includes the following steps: steam injection / huffing into the target reservoir using steam, wherein the steam is superheated steam, saturated steam, or wet steam, and the steam injection rate is calculated using the following formula: In the formula, M 汽 The mass of steam is represented by T, k is a correction factor, and T is the mass of steam. 原始 T represents the original formation temperature. 目标 Indicates the target temperature, C 油 M represents the specific heat capacity of the underground crude oil in the target reservoir. 油 C represents the mass of underground crude oil within the steam field's reach. 水1 M represents the specific heat capacity of formation water in the target oil reservoir. 水 C represents the mass of formation water within the steam-bearing area. 岩石 M represents the specific heat capacity of the rock framework in the target reservoir. 岩石 C represents the mass of the rock framework within the steam-borne range. 汽 T represents the specific heat capacity of steam. 汽 T represents the temperature of the steam. 饱和 C represents the temperature of saturated vapor at a depth within the target oil reservoir under formation pressure conditions. 水2 L represents the specific heat capacity of saturated water under formation pressure conditions at the middle depth of the target oil reservoir. v This represents the heat released when steam condenses into saturated water under formation pressure conditions at the middle depth of the target oil reservoir, where n is a parameter related to the steam huff and puff cycle.

2. The method for designing steam injection parameters in steam huff and puff oil recovery as described in claim 1, characterized in that, The target temperature is the temperature corresponding to a crude oil viscosity in the target reservoir that is no greater than 2000 mPa·s.

3. The method for designing steam injection parameters in steam huff and puff oil recovery as described in claim 1, characterized in that, When the target reservoir is a shallow reservoir, k = 1.1 to 1.2; when the target reservoir is a water-edge reservoir, k = 1.25 to 1.

3.

4. The method for designing steam injection parameters in steam huff and puff oil recovery as described in claim 1, characterized in that, When the steam injection cycle is no greater than 5, n = steam injection cycle; when the steam injection cycle is greater than 5, n = 5.

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