A method for calculating imbibition production of fractured reservoirs based on historical injection-production data

Abstract

The application provides a fracture reservoir imbibition production calculation method based on historical injection-production data, and belongs to the technical field of oilfield development, and comprises the following steps: step 1, collecting geological reservoir parameters of a target oilfield, dividing a calculation time step, and arranging injection-production historical data of each time step; step 2, calculating the average water saturation of a fracture system; step 3, calculating the water storage of the fracture system and the matrix system; step 4, calculating the cumulative oil production and daily oil production of the matrix system and the fracture system; step 5, calculating the recovery degree of the matrix system and the fracture system; and step 6, based on the calculation results of steps 4 and 5, evaluating the development effect of the oilfield. The method can quickly calculate the imbibition production and recovery degree of the fracture reservoir, provides technical support and theoretical guidance for formulating the development technical policy of the fracture reservoir, improves the development effect of the fracture oilfield, and is suitable for the fracture water injection development oilfield.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of oilfield development, and particularly relates to a method for calculating imbibition production of fractured reservoirs based on historical injection-production data. BACKGROUND

[0002] Fractured reservoirs are composed of matrix systems and fracture systems. Since the permeability of fracture systems is much larger than that of matrix systems, injected water mainly flows along the fracture systems during water injection development, and the fracture systems mainly rely on water drive pressure gradient to displace oil, while the matrix systems mainly rely on capillary force to make water in the fracture systems imbibed into the matrix systems to displace oil. Imbibition is an important mechanism of water drive development of fractured reservoirs. Periodic water injection and asynchronous oil production are combined to form an unstable pressure field to promote imbibition, thereby improving water drive recovery. Therefore, it is of great significance to study the imbibition production law and recovery for formulating development technical policies of fractured reservoirs.

[0003] At present, the methods for studying imbibition include laboratory experiments and numerical simulation, and the research is mainly carried out from the aspects of imbibition mechanism, law and characteristics. However, there are few studies on imbibition production and recovery of a specific target oilfield. In addition, due to the complex and dynamic changes of imbibition mechanism, the current research cannot reflect the dynamic changes of imbibition production and recovery degree of fractured reservoirs during development with the adjustment of injection well and production well working system, and it is difficult to effectively and directly guide the field work.

[0004] In order to solve the problems of the current technology, a method for calculating imbibition production of fractured reservoirs based on historical injection-production data is provided, which can quickly calculate the imbibition production and recovery degree of fractured reservoirs and guide the development of fractured reservoirs. SUMMARY

[0005] Therefore, the present application aims to provide a method for calculating imbibition production of fractured reservoirs based on historical injection-production data. Based on historical injection-production data, the method is started from the water drive law of fracture systems and the imbibition mechanism of matrix systems, and the water saturation and water storage of fracture systems and matrix systems are calculated according to the water drive oil theory and the material balance principle. Finally, the production and recovery degree of fracture systems and matrix systems are calculated, which can quickly calculate the imbibition production and recovery degree of fractured reservoirs and guide the development of fractured reservoirs.

[0006] To achieve the above-mentioned purpose, the technical scheme of the present application is as follows: a method for calculating imbibition production of fractured reservoirs based on historical injection-production data, comprising the following steps:

[0007] Step 1: collecting geological reservoir parameters of a target oilfield, dividing calculation time steps, and arranging injection-production historical data of each time step;

[0008] Step 2: calculating the average water saturation of fracture systems;

[0009] Step 3: Calculate the water storage in the crack system and the matrix system;

[0010] Step 4: Calculate the cumulative oil production and daily oil production of the matrix system and fracture system;

[0011] Step 5: Calculate the recovery extent of the matrix system and fracture system;

[0012] Step 6: Based on the calculation results of Steps 4 and 5, evaluate the oilfield development effect.

[0013] Furthermore, in step 1, geological reservoir characteristic parameters of the target oilfield are collected and organized, including the total geological reserves of the target oilfield or block, the proportion of the fracture system and matrix system in the total reserves, the pore volume of the fracture system, the pore volume of the matrix system, the relative permeability data of the fracture system, the viscosity of the formation crude oil, and the viscosity of the formation water.

[0014] Furthermore, in step 1, dividing the calculation time step refers to dividing the calculation time step according to the development history and characteristics of the target oil field or block. The calculation time step can be a year, half a year, quarter, or month.

[0015] Furthermore, in step 1, the historical injection and production data for each time step are compiled, including oil production, water production, water injection, water cut, and recovery degree.

[0016] Furthermore, in step 2, the formula for calculating the average water saturation of the fracture system at each time step is:

[0017]

[0018] In equation (1), the subscript f represents the crack system; S represents the average water saturation of the fracture system, a decimal. wfe f is the water saturation of the fracture system at the production well, a decimal. w (S wef f' represents the water cut of the production well, in %; w (S wef () is the decimal derivative of the water cut of the production well.

[0019] Furthermore, in step 3, the formula for calculating the water volume of the fracture system at each time step is:

[0020]

[0021] In equation (2), W f The water storage capacity of the crack system is 10,000 cubic meters; V f S represents the pore volume of the fracture system, in cubic meters; wcf The bound water saturation of the fracture system is a decimal.

[0022] Further, in step 3, the water storage amount of the matrix system at each time step is calculated by the following formula:

[0023] W m = W i -N w -W f (3)

[0024] In formula (3), subscript m represents the matrix system; W m is the water storage amount of the matrix system, million cubic meters; W i is the cumulative water injection amount of the injection well (injection end), million cubic meters; N w is the cumulative water production amount of the production well (production end), million cubic meters.

[0025] Further, in step 4, the cumulative oil production amount of the matrix system at each time step is equal to the cumulative water storage amount of the matrix system, that is, according to the imbibition mechanism, the water entering the matrix system displaces the same volume of crude oil, and the calculation formula is as follows:

[0026] N pm = W m (5)

[0027] The daily oil production amount of the matrix system at the kth time step is calculated by the following formula:

[0028] q m(k) = [N pm(k) -N pm(k)-1) ] / T (k) (6)

[0029] The cumulative oil production amount of the fracture system is calculated by the following formula:

[0030] N pf = N p -N pm (7)

[0031] The daily oil production amount of the fracture system at the kth time step is calculated by the following formula:

[0032]

[0033] In formulas (5) to (8), k represents the kth time step; N pm is the cumulative oil production amount of the matrix system, million cubic meters; q m is the daily oil production amount of the matrix system, million cubic meters per day; N pf is the cumulative oil production amount of the fracture system, million cubic meters; q f is the daily oil production amount of the fracture system, million cubic meters per day; N p is the cumulative oil production amount of the production well (production end), million cubic meters; and T is the production days of each time step, days.

[0034] Further, the step 5, the matrix system is the k time step of the recovery degree formula:

[0035]

[0036] The fracture system is the k time step of the recovery degree formula:

[0037]

[0038] In formula (9)~formula (10), R m The matrix system recovery degree, %;N m The matrix system geological reserves, million cubic meters;R f The fracture system recovery degree, %;N f The fracture system geological reserves, million cubic meters.

[0039] Compared with the prior art, the fracture reservoir imbibition production calculation method based on historical injection-production data has the following advantages: the fracture reservoir imbibition production calculation method based on historical injection-production data is based on historical injection-production data, and the average water saturation and water storage of the fracture system and the matrix system are calculated according to the water drive oil theory and the material balance principle based on the water drive law of the fracture system and the imbibition mechanism of the matrix system. Finally, the production and recovery degree of the fracture system and the matrix system are calculated, the fracture reservoir imbibition production and recovery degree can be quickly calculated, technical support and theoretical guidance are provided for formulating fracture reservoir development technical policy, the development effect of the fractured oilfield is improved, and the method is suitable for fracture water injection development oilfield. BRIEF DESCRIPTION OF DRAWINGS

[0040] The drawings constituting a part of the present application are used to provide further understanding of the present application, the illustrative embodiments of the present application and the description thereof are used to explain the present application, and do not constitute improper limitation on the present application. In the drawings:

[0041] Figure 1 It is the injection-production schematic diagram of Bohai JZS buried hill reservoir of the embodiment of the present application;

[0042] Figure 2 It is the fracture system relative permeability curve of Bohai JZS buried hill reservoir of the embodiment of the present application;

[0043] Figure 3 It is the water storage change curve of the matrix system and the fracture system of Bohai JZS buried hill reservoir of the embodiment of the present application;

[0044] Figure 4 It is the water saturation change curve of the matrix system and the fracture system of Bohai JZS buried hill reservoir of the embodiment of the present application;

[0045] Figure 5The oil production change curve of the matrix system and the fracture system of the Bohai JZS buried hill reservoir in the embodiment of the present application;

[0046] Figure 6 The recovery degree change curve of the matrix system and the fracture system of the Bohai JZS buried hill reservoir in the embodiment of the present application.

[0047] Explanation of reference signs:

[0048] 1, water injection well; 2, injected water of the water injection well; 3, production well; 4, produced water of the production well; 5, fracture system; 6, injected water into the fracture system; 7, matrix system; 8, injected water into the matrix system. DETAILED DESCRIPTION

[0049] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0050] The core of the fracture reservoir imbibition production calculation method based on historical injection and production data is to calculate the average water saturation and water storage of the fracture system and the matrix system according to the water drive oil theory and the material balance principle based on the fracture system water drive law and the matrix system imbibition mechanism, and finally to calculate the production and recovery degree of the fracture system and the matrix system. The specific process is as follows:

[0051] The present application is a fracture reservoir imbibition production calculation method based on historical injection and production data, comprising the following steps:

[0052] Step 1, collecting target oilfield geological reservoir parameters, dividing calculation time steps, and arranging injection and production historical data of each time step;

[0053] Among them, the target oilfield geological reservoir characteristic parameters are collected and arranged, including the total geological reserves of the target oilfield or block, the proportion of the fracture system and the matrix system in the total reserves, the fracture system pore volume, the matrix system pore volume, the fracture system relative permeability data, the formation crude oil viscosity, and the formation water viscosity;

[0054] The calculation time step is divided according to the development process and characteristics of the target oilfield or block, and the calculation time step can be year, half year, quarter, month;

[0055] The injection and production historical data of each time step includes oil production, water production, water injection, water cut, and recovery degree.

[0056] Step 2, calculating the average water saturation of the fracture system;

[0057] Among them, the average water saturation calculation formula of the fracture system at each time step is:

[0058]

[0059] In formula (1), subscript f represents the fracture system; Sf is the average water saturation of the fracture system, decimal; wef Sf is the water saturation of the fracture system at the production well (production end), decimal; w Sf is the water saturation of the fracture system at the production well (production end), decimal; wef Sf is the water saturation of the fracture system at the production well (production end), decimal; w Sf is the water saturation of the fracture system at the production well (production end), decimal. wef Sf is the water saturation of the fracture system at the production well (production end), decimal.

[0060] Step 3, calculate the water storage of the fracture system, matrix system;

[0061] In formula (2), Wf is the water storage of the fracture system at each time step, million cubic meters; Vf is the pore volume of the fracture system, million cubic meters; Sf is the irreducible water saturation of the fracture system, decimal; and Nf is the cumulative injection volume of the injection well (injection end), million cubic meters.

[0062]

[0063] In formula (2), Wf is the water storage of the fracture system at each time step, million cubic meters; Vf is the pore volume of the fracture system, million cubic meters; Sf is the irreducible water saturation of the fracture system, decimal; and Nf is the cumulative injection volume of the injection well (injection end), million cubic meters. f Wf is the water storage of the fracture system, million cubic meters; Vf is the pore volume of the fracture system, million cubic meters; Sf is the irreducible water saturation of the fracture system, decimal. f Wf is the water storage of the fracture system, million cubic meters; Vf is the pore volume of the fracture system, million cubic meters; Sf is the irreducible water saturation of the fracture system, decimal. wcf Wf is the water storage of the fracture system, million cubic meters; Vf is the pore volume of the fracture system, million cubic meters; Sf is the irreducible water saturation of the fracture system, decimal.

[0064] In formula (4), Wm is the water storage of the matrix system at each time step, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal; and Nm is the cumulative injection volume of the injection well (injection end), million cubic meters.

[0065] Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. m Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. i Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. w Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. f Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal.

[0066] In formula (3), subscript m represents the matrix system; Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal; Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters. m Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. i Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal. w Wm is the water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal.

[0067] Step 4, calculate the cumulative oil production and daily oil production of the matrix system and the fracture system;

[0068] In formula (5), Wm is the cumulative water storage of the matrix system, million cubic meters; Vm is the pore volume of the matrix system, million cubic meters; Sm is the irreducible water saturation of the matrix system, decimal; and Nm is the cumulative injection volume of the injection well (injection end), million cubic meters.

[0069] Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters. pm Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters. m Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters.

[0070] In formula (6), Qm is the daily oil production of the matrix system at the kth time step, million cubic meters; and Nm is the cumulative injection volume of the injection well (injection end), million cubic meters.

[0071] Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters. m(k) Nm is the cumulative injection volume of the injection well (injection end), million cubic meters; and Qm is the cumulative production volume of the production well (production end), million cubic meters.pm(k) -N pm(k-1) ] / T (k) (6)

[0072] The cumulative oil production of the fracture system is calculated by the following formula:

[0073] N pf =N p -N pm (7)

[0074] The daily oil production of the fracture system at the kth time step is calculated by the following formula:

[0075] q f(k) =[N pf(k) -N pf(k-1) ] / T (k) (8)

[0076] In the formula (5) to formula (8), k represents the kth time step; N pm represents the cumulative oil production of the matrix system, 104m3; q m represents the daily oil production of the matrix system, m3 / d; N pf represents the cumulative oil production of the fracture system, 104m3; q f represents the daily oil production of the fracture system, m3 / d; N p represents the cumulative oil production of the production well (the output end), 104m3; and T represents the production days of each time step, d.

[0077] Step 5: The recovery degrees of the matrix system and the fracture system are calculated.

[0078] The recovery degree of the matrix system at the kth time step is calculated by the following formula:

[0079]

[0080] The recovery degree of the fracture system at the kth time step is calculated by the following formula:

[0081]

[0082] In the formula (9) to formula (10), R m represents the recovery degree of the matrix system, %; N m represents the geological reserves of the matrix system, 104m3; R f represents the recovery degree of the fracture system, %; N f represents the geological reserves of the fracture system, 104m3.

[0083] Step 6: The development effect of the oilfield is evaluated based on the calculation results of step 4 and step 5.

[0084] In order to better understand the invention content, characteristics and effects of the present application, the following examples are given and described in detail as follows with reference to the accompanying drawings:

[0085] First, the derivation process of the calculation method for the permeable production of fractured reservoirs based on historical injection and production data is briefly described. During the injection and production process of injection well 1 and production well 3, since the permeability of fracture system 5 is much greater than that of matrix system 7, it is assumed that the injected water 2 of the injection well mainly flows along fracture system 5 and flows into the wellbore of production well 3 in two parts: (1) Under the action of capillary force, part of the injected water 6 that enters the fracture system enters the matrix rock from fracture system 5 and remains there (becoming the injected water 8 that enters the matrix system), replacing an equal amount of crude oil into fracture system 5, and then flows into the wellbore of production well 3 from fracture system 5, becoming the produced water 4 of the production well, ignoring the matrix system 7 and flowing directly into the wellbore; (2) Under the displacement pressure of fracture system 5, another part of the injected water 6 that enters the fracture system enters the wellbore of production well 3 from fracture system 5, becoming the produced water 4 of the production well. Figure 1 As shown, the above-mentioned water drive process is studied using a fractured reservoir with one injection and one production as an example.

[0086] During waterflooding development, the water cut of the production well (production end) depends on the water saturation of the fracture system. Therefore, changes in the water cut of the production well (production end) reflect the water saturation status of the fracture system. According to the Welge equation, the average water saturation of the oil-water two-phase region of the fracture system is:

[0087]

[0088] In equation (1), the subscript f represents the crack system; S represents the average water saturation of the fracture system, a decimal. wfe f is the water saturation of the fracture system at the production well (producing end), a decimal. w (S wef f' represents the water cut of the production well (output end), in %; w (S wef ) is the decimal derivative of the water cut of the production well (producing end).

[0089] As water is continuously injected, the water volume in the fracture system increases with the increase of the average water saturation of the fracture system. The water volume in the fracture system is:

[0090]

[0091] In equation (2), W f The water storage capacity of the crack system is 10,000 cubic meters; V f S represents the pore volume of the fracture system, in cubic meters; wcf The bound water saturation of the fracture system is a decimal.

[0092] According to the principle of conservation of mass, the cumulative water injection amount of the injection well (injection end) is equal to the sum of the fracture system water storage amount, the matrix system water storage amount and the cumulative water production amount of the production well (production end), so the matrix system water storage amount is:

[0093] W m = W i -N w -W f (3)

[0094] In formula (3), subscript m represents the matrix system; W m is the matrix system water storage amount, million cubic meters; W i is the cumulative water injection amount of the injection well (injection end), million cubic meters; N w is the cumulative water production amount of the production well (production end), million cubic meters.

[0095] The average water saturation of the matrix system is:

[0096]

[0097] In formula (4), S is the average water saturation of the matrix system, decimal; W m is the matrix system water storage amount, million cubic meters; V m is the pore volume of the matrix system, million cubic meters.

[0098] According to the mechanism of imbibition, under the action of capillary force, the water entering the matrix system is retained and replaces an equal amount of crude oil, that is, the matrix system water storage amount is equal to the cumulative oil production amount of the matrix system, so the cumulative oil production amount of the matrix system is:

[0099] N pm = W m (5)

[0100] The daily oil production amount of the matrix system at the kth time step is:

[0101] q m(k) = [N pm(k) -N pm(k-1) ] / T (k) (6)

[0102] The cumulative oil production amount of the fracture system is:

[0103] N pf = N p -N pm (7)

[0104] The daily oil production amount of the fracture system at the kth time step is:

[0105] q f(k) = [N pf(k) -N pf(k-1) ] / T(k) (8)

[0106] In equations (5) to (8), k represents the kth time step; N pm The cumulative oil production of the matrix system is in ten thousand cubic meters; q m The daily oil production of the matrix system is expressed in cubic meters per day (N). pf The cumulative oil production of the fracture system is 10,000 cubic meters; q f The daily oil production of the fracture system is expressed in cubic meters per day (N). p T represents the cumulative oil production of the production well (producing end), in ten thousand cubic meters; T represents the number of production days at each time step, in days.

[0107] The recovery degree of the matrix system at time step k is:

[0108]

[0109] The recovery level of the fracture system at time step k is:

[0110]

[0111] In equations (9) to (10), R m The degree of recovery of the matrix system, %; N m Geological reserves of the matrix system, 10,000 cubic meters; R f The degree of recovery of the fracture system, %; N f The geological reserves of the fracture system are 10,000 cubic meters.

[0112] The specific calculation process is as follows:

[0113] ① Collect geological and reservoir parameters of the target oilfield, divide the calculation time steps, and organize the injection and production historical data of each time step;

[0114] ② Given the water cut f of the production well (producing end) w (S wef Under the conditions of parameters such as the relative permeability curve of the fracture system, the water cut f of the production well (production end) is calculated using equation (1). w (S wef The corresponding average water saturation of the fracture system Further use equation (2) to calculate the water storage capacity W of the crack system. f ;

[0115] ③ Given the known water injection volume W at the injection well (injection end) i Production well (output end) water production N W Under the condition of historical injection and extraction data, the water storage capacity W of the matrix system is calculated using equations (3), (4), (5), (6), and (9), respectively. m Average water saturation Cumulative oil production N pm, daily oil production q m , recovery factor R m ;

[0116] ④ Calculate the cumulative oil production N of the fracture system respectively by formula (7), formula (8) and formula (10) pf , daily oil production q f , recovery factor R f ;

[0117] ⑤ Calculate according to ②-④ at each time step.

[0118] The application process and effect of the present application are introduced below by taking Bohai JZS buried hill reservoir as an example. The main producing layer of the reservoir is Archean metamorphic buried hill, which has the characteristics of fracture development and strong heterogeneity; the average total porosity of the reservoir interpreted by well logging is 6.80%, the average fracture porosity is 1.08%, the average permeability is 500 mD, the average porosity of the matrix system is 5.72%, and the permeability is less than 1 mD; the oil geological reserves of the matrix system account for 75% of the total oil geological reserves; the underground crude oil viscosity is 2.3 mPa·s. In the first phase, the horizontal well top-bottom staggered well pattern is developed, the oil geological reserves of 20 million cubic meters are produced, 4 injection wells and 9 production wells are implemented, and the production is put into operation in December 2009.

[0119] Step 1, briefly describe the process of collecting and organizing target reservoir geological reservoir parameters, injection and production history data.

[0120] Since the production of A reservoir, it has experienced three stages of depressurization production, periodic water injection and asynchronous injection and production, and has realized water control and oil stabilization by taking unstable injection and production measures. As of December 2021, the comprehensive water content is 55%, the recovery factor is 22.5%, and the oil production rate is 1.0%. According to the development process and characteristics, the calculation time step is divided by year, and the annual injection and production data are arranged, as shown in Table 1.

[0121] Table 1 is the historical injection and production data of Bohai JZS buried hill reservoir in the embodiment of the present application

[0122]

[0123] Step 2, briefly describe the calculation process and results of the average water saturation and water storage of the fracture system and the matrix system at each time step.

[0124] The relative permeability curve of the fracture system of A reservoir is shown in Figure 2 , the water saturation S w corresponding to a certain water content rate f wfe of the production well (output end) and the derivative f' w of the water content rate of the production well (output end) (S wef ) are calculated, and then formula (1) is used to calculate the water content rate f wThe corresponding fracture system average water saturation Finally, the corresponding fracture system water storage W is calculated using formula (2) f After calculating the fracture system average water saturation and water storage, the matrix system water storage W m and average water saturation S

[0125] With the deepening of oilfield development, the injection water is continuously injected, and the water content of the oilfield gradually rises. As shown in Figs. 1 and 2, the water drive characteristics of the matrix system and the fracture system are as follows: Figure 3 , Figure 4

[0126] ① In the low water cut development stage (water cut less than 30%), the injected water mainly enters the fracture system, and the fracture system water storage and average water saturation increase rapidly. At this time, the reservoir output is mainly from the fracture system, and the matrix system is in the initial stage of imbibition, so the matrix system water storage and average water saturation increase slowly, and the matrix system output is small.

[0127] ② In the medium water cut development stage (water cut 30% to 60%), the matrix rock is gradually surrounded by water in the fracture system, and the imbibition effect begins and gradually strengthens. The injected water gradually enters the matrix rock from the fracture system and is retained, and at the same time, the same amount of oil is displaced, so the matrix system water storage and system water saturation increase rapidly. Due to the imbibition of oil from the matrix rock, the oil in the matrix rock enters the fracture system, resulting in a slow increase in the fracture water saturation, and the development characteristics of the water cut rise slowly, remain unchanged or even decrease.

[0128] Step 3, briefly describe the calculation process and results of the cumulative oil production, daily oil production and recovery degree of the fracture system and the matrix system at each time step.

[0129] According to the imbibition mechanism, the injected water enters the matrix rock from the fracture system and is retained, and the same amount of oil is replaced, i.e. the matrix system water storage is equal to the cumulative oil production of the matrix system. The cumulative oil production N pm of the matrix system is calculated using formula (5), and then the daily oil production q m and recovery degree R m of the matrix system are calculated using formula (6) and formula (9). According to the principle of conservation of mass, the total cumulative oil production is equal to the cumulative oil production N pm of the matrix system N pf , so the cumulative oil production N pf of the fracture system is calculated using formula (7), and then the daily oil production q f and recovery degree R f of the fracture system are calculated using formula (8) and formula (10). The settlement results are shown in Figs. 3 to 6.​Figure 5 , Figure 6 As shown, the development characteristics of the matrix system and fracture system are as follows:

[0130] ① In the early stage of production (2010-2013), the reservoir mainly relied on the release of elastic energy from the fracture system for oil supply. The oil production rate of the fracture system was greater than 80%, but the decline rate was large. During this stage, the recovery rate of the fracture system reached 40%, while the recovery rate of the matrix system was only 3%.

[0131] ② In the mid-water-cut development stage (2013-2021), in response to the problems of large production decline and rapid increase in water cut, measures such as periodic water injection and asynchronous oil production were adopted. The permeation of the matrix rock began and gradually increased, and the oil production ratio of the matrix system gradually increased to more than 80%, while the oil production ratio of the fracture system gradually decreased (about 20%). Since the oil geological reserves of the matrix system account for 75% of the total geological reserves, the degree of oil production contribution of the matrix system in this stage directly affects the development effect of fractured reservoirs. The recovery rate of the matrix system in this stage reached more than 10%.

[0132] Finally, based on the calculation results of steps 2 and 3 in the above embodiments, the understanding and conclusions of the development effect evaluation of reservoir A are briefly described.

[0133] In the initial stage of development of the A-type buried hill reservoir, depressurization was employed to fully utilize the elasticity of the fracture system, achieving a relatively high annual oil production rate (3%–4%). In the first three years, the fracture recovery rate reached approximately 40%. As water cut gradually increased, unstable injection-production measures were implemented to fully leverage the seepage and drainage function of the matrix system, achieving water control and oil stabilization during the medium-to-high water cut period. The oilfield's oil production rate remained at around 1%, and the matrix system recovery rate reached over 10% during this stage. Based on the effectiveness of these measures, it is recommended that the next step continue with a combination of periodic water injection and asynchronous oil production to strengthen the seepage and drainage function of the matrix system, significantly improving its production capacity. The predicted water-drive recovery rate is 32%, the matrix system recovery rate is 23%, and the fracture system recovery rate is 60%. This invention, based on historical injection-production data, can quickly and conveniently calculate the water storage, water saturation, production, and recovery rate of the fracture system and matrix system during water injection development in fractured reservoirs, objectively evaluating their production capacity and recovery rate.

[0134] Although preferred embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other modifications under the guidance of the present invention without departing from the spirit and scope of the claims, and all of these modifications are within the scope of protection of the present invention.

Claims

1. A method for calculating the permeation production of fractured reservoirs based on historical injection-production data, characterized in that, Includes the following steps: Step 1: Collect geological and reservoir parameters of the target oilfield, divide the calculation time steps, and organize the injection and production historical data for each time step; Step 2: Calculate the average water saturation of the fracture system; The formula for calculating the average water saturation of the fracture system at each time step is as follows: （1） In equation (1), the subscript f represents the crack system; The average water saturation of the fracture system, a decimal. The water saturation of the fracture system at the production well is a decimal. The water cut of the production well, % This is the derivative of the water cut of the production well, a decimal. Step 3: Calculate the water storage in the crack system and the matrix system; The formula for calculating the water volume at each time step of the fracture system is as follows: （2） In equation (2), The water storage capacity of the crack system is 10,000 cubic meters. The pore volume of the fracture system is in ten thousand cubic meters. The bound water saturation of the fracture system is a decimal. The formula for calculating the water storage at each time step of the substrate system is as follows: （3） In equation (3), the subscript m represents the matrix system; The water storage capacity of the substrate system is 10,000 cubic meters. The cumulative water injection volume of the injection well is 10,000 cubic meters. The cumulative water production of the production well is 10,000 cubic meters. Step 4: Calculate the cumulative oil production and daily oil production of the matrix system and fracture system; The cumulative oil production at each time step of the matrix system is equal to the cumulative water volume in the matrix system. That is, according to the percolation mechanism, the water entering the matrix system displaces the same volume of crude oil. The calculation formula is as follows: （5） The formula for calculating the daily oil production of the matrix system at the k-th time step is: （6） The formula for calculating the cumulative oil production of a fracture system is: （7） The formula for calculating the daily oil production at the k-th time step of the fracture system is: （8） In equations (5) to (8), k represents the kth time step; The cumulative oil production of the matrix system is in tens of thousands of cubic meters. This represents the daily oil production of the matrix system, in cubic meters per day. The cumulative oil production of the fracture system is 10,000 cubic meters. This represents the daily oil production of the fracture system, in cubic meters per day. T represents the cumulative oil production of the production well, in ten thousand cubic meters; T represents the number of production days at each time step, in days. Step 5: Calculate the recovery extent of the matrix system and fracture system; The formula for calculating the recovery rate of the matrix system at the k-th time step is: （9） The formula for calculating the recovery level of the fracture system at the k-th time step is: （10） In equations (9) to (10), The degree of recovery of the matrix system, % Geological reserves of the matrix system, 10,000 cubic meters; The degree of recovery of the fractured system, % The geological reserves of the fracture system are in the tens of thousands of cubic meters. Step 6: Based on the calculation results of Steps 4 and 5, evaluate the oilfield development effect.

2. The method for calculating the permeation production of fractured reservoirs based on historical injection and production data according to claim 1, characterized in that: In step 1, geological reservoir characteristic parameters of the target oilfield are collected and organized, including the total geological reserves of the target oilfield or block, the proportion of the fracture system and matrix system in the total reserves, the pore volume of the fracture system, the pore volume of the matrix system, the relative permeability data of the fracture system, the viscosity of the formation crude oil, and the viscosity of the formation water.

3. The method for calculating the permeation production of fractured reservoirs based on historical injection and production data according to claim 1, characterized in that: In step 1, dividing the calculation time step refers to dividing the calculation time step according to the development history and characteristics of the target oil field or block. The calculation time step can be a year, half a year, quarter, or month.

4. The method for calculating the permeation production of fractured reservoirs based on historical injection and production data according to claim 1, characterized in that: In step 1, the historical injection and production data for each time step are compiled, including oil production, water production, water injection, water cut, and recovery degree.

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