Method and system for determining oil-gas interface of salt cavern oil storage

Abstract

The invention relates to the technical field of salt cavern oil and gas storage, and discloses a method and system for determining an oil and gas interface of a salt cavern oil storage. The method comprises the steps of determining a first relational expression of gas cap pressure and oil-gas interface depth before and after an oil injection process based on a real gas state equation; and determining a second relational expression between the oil-gas interface depth and the injection time, then solving based on the first relational expression and the second relational expression to obtain gas cap pressure, and obtaining the oil-gas interface depth, the oil body pressure and the bottom hole pressure according to the gas cap pressure. According to the method, changes of gas cap pressure and oil body pressure of the salt cavern oil storage can be accurately monitored in real time, the depth change of an oil-gas interface can be effectively judged, and reliable data support is provided for the oil-gas distribution and injection process of the salt cavern oil storage; and the possible leakage problem in the salt cavern can be known more safely and intuitively.

Description

Technical Field

[0001] The present application relates to the field of salt cavern oil and gas storage, and in particular to a method and system for determining an oil and gas interface in a salt cavern oil storage depot. Background Art

[0002] Salt rock is a very stable rock with dense structure, low permeability, plasticity under high temperature and high pressure, excellent damage self-repair and creep properties, which can effectively prevent the leakage of stored liquid. Salt rock often presents a layered structure with considerable thickness underground, and its location is generally in the lower area of ​​the sedimentary rock layer. In the long geological history, affected by geological pressure and temperature, salt rock has constructed an underground space environment with uniform texture and solid structure. Therefore, salt cavern oil storage is favored by various countries. However, in the actual application of salt cavern oil storage, with the continuous injection of crude oil, the air pressure inside is compressed, and the gas cap pressure will also increase. Therefore, accurately locating the oil-gas interface is a key issue. Its position change directly affects the storage efficiency, operation safety and resource utilization of the reservoir. At present, traditional oil-gas interface detection methods, such as liquid level measurement and electromagnetic wave detection, have the problems of high testing cost, low testing accuracy, slow response and susceptibility to environmental interference, which are difficult to meet the requirements of modern salt cavern oil storage for high-precision monitoring and real-time performance. Summary of the invention

[0003] The present application provides a method for determining the oil-gas interface in a salt cavern oil reservoir, so as to solve the problems in the prior art that the traditional oil-gas interface detection method has high testing cost, low testing accuracy, slow response and susceptibility to environmental interference.

[0004] In order to solve the above technical problems, the present application discloses a method for determining the oil-gas interface of a salt cavern oil reservoir, the method comprising:

[0005] Based on the real gas state equation, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process is determined;

[0006] Determine the second relationship between the oil-gas interface depth and the injection time;

[0007] The gas cap pressure is obtained by solving the first relation and the second relation;

[0008] The oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure.

[0009] Preferably, the first relation is:

[0010]

[0011] Among them, p k(t) is the gas cap pressure; t is the injection time; H is the total depth of the salt cavern oil reservoir; p k0 is the initial pressure of the gas cap; h is the height of the oil body, Hh is the depth of the oil-gas interface; z is the altitude coordinate of the corresponding depth; r is the radius corresponding to the depth z.

[0012] Preferably, determining the second relationship between the oil-gas interface depth and the injection time comprises:

[0013] The surface injection volume qt is calculated by the volume coefficient B and the gas cap pressure p k After conversion of (t), the effective volume in the salt cavern oil storage tank is qtB(p k (t));

[0014] The relationship between the oil-gas interface depth and the injection time is expressed by the change relationship between the oil phase volume and the oil-gas interface depth, and the second relationship is determined:

[0015]

[0016] Where q is the injection speed.

[0017] Preferably, obtaining the gas cap pressure based on the first relationship and the second relationship includes:

[0018] The first relation is transformed into:

[0019]

[0020] After finishing, we can get:

[0021]

[0022] Then transform the integral interval of formula (4) to obtain:

[0023]

[0024] After finishing, we get:

[0025]

[0026] The coordinate transformation of the second relation is:

[0027]

[0028] Substituting formula (6) into formula (7) yields:

[0029]

[0030] When a certain time t0 is given, the unknown quantity p k (t0) is a certain value, recorded as x, then the solution equation is determined:

[0031]

[0032] To solve the equation, iterative x is used to calculate the gas cap pressure p at any time t0 k (t0).

[0033] Preferably, the solution equation is solved by iterative x solution to calculate the gas cap pressure p at any time t0 k (t0), including:

[0034] Determine the time t0=t(k) of this iteration; where k represents the current iteration number, and k=1 for the initial iteration;

[0035] Calculate the current iteration time, x0(t0) = p k (t);

[0036] If the absolute value of F(x0) is less than e, calculate and output p k (t) = x0, otherwise x0 = x0 + Δp, and re-determine whether the absolute value of F(x0) is less than e.

[0037] Preferably, the oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure, including:

[0038] Based on the gas cap pressure and the first relation, the depth of the oil-gas interface is obtained;

[0039] Calculate the oil pressure according to the depth of the oil-gas interface;

[0040] The bottom hole pressure is calculated based on the gas cap pressure and oil body pressure.

[0041] Preferably, calculating the oil pressure according to the oil-gas interface depth includes:

[0042] The oil body height is calculated based on the total depth of the salt cavern oil reservoir and the depth of the oil-gas interface:

[0043] h=H-(Hh)

[0044] Among them, H is the total depth of the salt cavern oil reservoir, and Hh is the depth of the oil-gas interface;

[0045] The oil pressure is calculated based on the oil height:

[0046]

[0047] Among them, p i (t) is the oil pressure; ρ o is the density of crude oil; c is the compression coefficient of crude oil, and g is the acceleration of gravity.

[0048] Preferably, the bottom hole pressure is calculated according to the gas cap pressure and the oil body pressure, including:

[0049] Add the gas cap pressure and the oil body pressure to obtain the bottom hole pressure:

[0050] p w (t) = p k (t)+p i (t) (11)

[0051] Among them, p k (t) is the gas cap pressure, p i (t) is the oil pressure, p w (t) is the bottom hole pressure.

[0052] The present application also discloses a system for determining the oil-gas interface of a salt cavern oil reservoir, the system comprising:

[0053] A mathematical model building module, used to determine the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process based on the real gas state equation;

[0054] The mathematical model building module is also used to determine a second relationship between the oil-gas interface depth and the injection time;

[0055] A data acquisition module, used for solving the gas cap pressure based on the first relationship and the second relationship;

[0056] The data acquisition module is also used to obtain the oil-gas interface depth, oil body pressure and bottom hole pressure according to the gas cap pressure.

[0057] Preferably, the system further comprises a plurality of groups of optical fiber sensors and acoustic wave sensors arranged on the side walls of the salt cavern oil storage depot.

[0058] In the present application, based on the real gas state equation, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process is determined; the second relationship between the oil-gas interface depth and the injection time is determined, and then the gas cap pressure is obtained based on the first relationship and the second relationship, and the oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure. The method in the present application can accurately monitor the changes in the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, obtain the oil surface parameters, and thus effectively judge the depth changes of the oil-gas interface, and provide reliable data support for the oil and gas distribution and injection process of the salt cavern oil reservoir, and the monitoring cost is low. The method can also monitor the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, and can more safely and intuitively understand the leakage problems that may occur inside the salt cavern.

[0059] Additional aspects and advantages of the present application will be given in the following description, which will become apparent from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0061] Figure 1 A schematic diagram of the oil storage process in a salt cavern oil storage tank provided in an embodiment of the present application;

[0062] Figure 2 A flow chart of a method for determining the oil-gas interface of a salt cavern oil reservoir provided in an embodiment of the present application;

[0063] Figure 3 A flow chart for calculating the gas cap pressure at any time provided in an embodiment of the present application;

[0064] Figure 4 A schematic diagram of the structure of a salt cavern oil storage tank provided in an embodiment of the present application;

[0065] Figure 5 A diagram showing bottom hole pressure detection results at different injection times provided in an embodiment of the present application;

[0066] Figure 6 A graph showing gas cap pressure detection results at different injection times provided in an embodiment of the present application;

[0067] Figure 7 A diagram showing the oil-gas interface depth detection results at different injection times provided in the embodiment of the present application;

[0068] Figure 8 A schematic diagram of the structure of a system for determining the oil-gas interface of a salt cavern oil storage reservoir provided in an embodiment of the present application. DETAILED DESCRIPTION

[0069] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present application, and cannot be interpreted as limiting the present application.

[0070] It will be understood by those skilled in the art that, unless expressly stated, the singular forms "one", "said", and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present application refers to the presence of features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be an intermediate element. In addition, the "connection" or "coupling" used herein may include wireless connection or wireless coupling. The term "and / or" used herein includes all or any unit and all combinations of one or more associated listed items.

[0071] Those skilled in the art will appreciate that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the field to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless specifically defined as here.

[0072] With regard to the technical problems existing in the prior art, the present application provides a method and system for determining the oil-gas interface in a salt cavern oil storage reservoir, aiming to solve at least one of the technical problems in the prior art.

[0073] The technical solution of the present application and how the technical solution of the present application solves the above-mentioned technical problems are described in detail below with specific embodiments. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below in conjunction with the accompanying drawings.

[0074] like Figure 1 As shown in the figure, the salt cavern reservoir is a cavity with an arbitrary cross section that is approximately circular, with a depth of H and a radius r(z) corresponding to an arbitrary depth z (the altitude coordinate with the ground as the zero point). Crude oil is injected into the salt cavern reservoir through an injection well. Before the crude oil is injected, there is a certain pressure of gas inside the salt cavern reservoir, and its pressure is recorded as p k0 At present, there is no relevant report on the internal pressure monitoring of the injection process of the salt cavern oil reservoir. In order to fill this technical gap, a method for determining the oil-gas interface of the salt cavern oil reservoir is proposed in the embodiment of the present application, which is used to obtain the oil-gas interface depth Hh(t) and gas cap pressure p at any time t. k (t), oil pressure p i (t) and the change of bottom hole pressure p w(t). Multiple groups of optical fiber sensors and acoustic wave sensors are used to monitor whether there are cracks in the wall.

[0075] like Figure 2 As shown in , the embodiment of the present application provides a method for determining the oil-gas interface of a salt cavern oil reservoir, and the method may include the following steps:

[0076] Step 201, based on the real gas state equation, determine a first relationship between the gas cap pressure and the oil body height before and after the oil injection process.

[0077] During the injection process, the injection well injects crude oil into the salt cavern reservoir at a constant injection rate q. The density of crude oil is ρ and the volume coefficient is B. At any time t during the injection process, the depth of the oil-gas interface is Hh(t), where H is the total depth of the salt cavern reservoir. At this time, the gas cap pressure is p k (t).

[0078] In the process of transporting oil into the salt cavern reservoir, it is assumed that this process is an ideal adiabatic process with no heat generation. The gas cap gas in the salt cavern reservoir does not dissolve in oil, and the real gas state equation PV=ZnRT is used to describe the process. Among them, P is pressure, V is volume, Z is gas compression factor, n is the amount of substance, R is molar gas constant, and T is temperature. As the oil injection process proceeds, the oil body in the salt cavern is gradually filled, and the oil-gas interface depth Hh(t) continues to rise, resulting in continuous compression of the gas cap volume. In this process, as the injection time t increases, the volume of the gas cap gradually decreases, and the gas cap pressure p k (t) also increases accordingly. At the beginning of oil injection, the oil depth in the salt cavern reservoir is H, that is, at the initial moment h0 = 0, and the initial pressure of the gas cap is p k0 As the oil is injected, the depth of the oil column continues to rise to Hh(t), and the gas cap pressure at this time is p k (t).

[0079] Through the real gas state equation PV = ZnRT, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process can be derived. The first relationship can help determine the location of the oil-gas interface, thereby effectively monitoring and predicting the oil and gas distribution state in the salt cavern oil reservoir.

[0080] Step 202, determining a second relationship between the oil-gas interface depth and the injection time.

[0081] In terms of the depth of the oil-gas interface under constant current injection, as the injection time increases, the oil level in the salt cavern gradually rises, and the oil-gas interface depth Hh changes continuously with the injection time t. Therefore, in the embodiment of the present application, the relationship between the oil-gas interface depth and the injection time is expressed by the second relational expression.

[0082] Step 203, obtaining the gas cap pressure by solving the first relational expression and the second relational expression;

[0083] Step 204, obtaining the oil-gas interface depth, oil body pressure and bottom hole pressure according to the gas cap pressure.

[0084] In the embodiment of the present application, after obtaining the gas cap pressure, the oil-gas interface depth can be calculated by the first relationship between the gas cap pressure and the oil-gas interface depth to determine the position of the oil-gas interface, so as to effectively monitor and predict the oil and gas distribution state in the salt cavern oil reservoir. In the embodiment of the present application, the gas cap pressure and oil body pressure of the salt cavern oil reservoir can also be monitored in real time, so that the leakage problem that may occur inside the salt cavern can be understood more safely and intuitively. When a leak occurs, the system can automatically identify and issue an early warning signal, so that relevant personnel can take timely intervention measures. For example, the energy resources in the salt cavern oil reservoir can be used preferentially to reduce the energy loss caused by the leak, thereby effectively alleviating the energy leakage problem of the salt cavern oil reservoir. This method provides technical guarantee for the safe operation of the salt cavern oil reservoir.

[0085] The method in the embodiment of the present application is not only applicable to the oil-gas interface monitoring of the salt cavern oil reservoir, but can also be extended to the scene of storing other types of energy in the salt cavern. For example, when burying energy such as carbon dioxide (CO2), hydrogen (H2) or helium (He) in the salt cavern oil reservoir, the system can also accurately monitor the gas and liquid pressure inside the salt cavern oil reservoir to ensure the safety and stability of different types of energy storage processes. Therefore, the method in the embodiment of the present application has wide applicability and high cost performance, and can meet the monitoring needs under different energy storage methods.

[0086] In the embodiment of the present application, based on the real gas state equation, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process is determined; the second relationship between the oil-gas interface depth and the injection time is determined, and then the gas cap pressure is obtained based on the first relationship and the second relationship, and the oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure. The method in the embodiment of the present application can accurately monitor the changes in the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, obtain oil surface parameters, and thus effectively judge the depth changes of the oil-gas interface, and provide reliable data support for the oil and gas distribution and injection process of the salt cavern oil reservoir, and the monitoring cost is low. The method can also monitor the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, and can more safely and intuitively understand the leakage problems that may occur inside the salt cavern.

[0087] In an optional embodiment, the first relation is:

[0088]

[0089] Among them, p k(t) is the gas cap pressure, Pa; t is the injection time, s; H is the total depth of the salt cavern oil reservoir, m; p k0 is the initial pressure of the gas cap, Pa; h is the height of the oil body, m; Hh is the depth of the oil-gas interface, m; z is the altitude coordinate of the corresponding depth, m; r is the radius corresponding to the depth z, m.

[0090] In an optional embodiment, determining the second relationship between the oil-gas interface depth and the injection time includes:

[0091] The surface injection volume qt is calculated by the volume coefficient B and the gas cap pressure p k After conversion of (t), the effective volume in the salt cavern oil storage tank is qtB(p k (t));

[0092] The relationship between the oil-gas interface depth and the injection time is expressed by the change relationship between the oil phase volume and the oil-gas interface depth, and the second relationship is determined:

[0093]

[0094] Where q is the injection speed, m 3 / s; B is the volume coefficient of crude oil.

[0095] Since the volume of the oil phase changes from the surface to the salt cavern, the total amount of crude oil injected from the surface is qt during the injection process, but the volume of this part of crude oil in the salt cavern will be affected by the pressure change. Specifically, the surface injection volume qt is calculated by the volume coefficient B and the gas cap pressure p k After conversion of (t), the effective volume in the salt cavern is qtB(p k (t)).

[0096] This injection volume causes an increase in the oil phase volume, which in turn leads to a decrease in the oil-gas interface depth Hh. Therefore, the relationship between the oil-gas interface depth and the injection time t can be expressed by the relationship between the oil phase volume change and the oil level h, thus generating the above second relationship.

[0097] In an optional embodiment, obtaining the gas cap pressure based on the first relationship and the second relationship includes:

[0098] The first relation is transformed into:

[0099]

[0100] After finishing, we can get:

[0101]

[0102] Then transform the integral interval of formula (4) to obtain:

[0103]

[0104] After finishing, we get:

[0105]

[0106] The coordinate transformation of the second relation is:

[0107]

[0108] Substituting formula (6) into formula (7) yields:

[0109]

[0110] From formula (8), we can see that there is only p on the left side of the equal sign. k (t) is the unknown quantity. On the right side of the equal sign is the gas cap pressure p k Implicit function of (t);

[0111] When a certain time t0 is given, the unknown quantity p k (t0) is a certain value, recorded as x, then the solution equation is determined:

[0112]

[0113] To solve the equation, iterative x is used to calculate the gas cap pressure p at any time t0 k (t0).

[0114] In an optional embodiment, if Figure 3 As shown, for solving the equation, iterative x is used to calculate the gas cap pressure p at any time t0 k (t0), including:

[0115] Determine the time t0=t(k) of this iteration; where k represents the current iteration number, and k=1 for the initial iteration;

[0116] Calculate the current iteration time, x0(t0) = p k (t);

[0117] If the absolute value of F(x0) is less than e, calculate and output p k (t) = x0, otherwise x0 = x0 + Δp, and re-determine whether the absolute value of F(x0) is less than e.

[0118] The total number of iterations is set to n. During the iteration process, if the total number of iterations is reached (i.e., k = n), the output gas top pressure p k (t), otherwise k=k+1, and the next iteration process is entered. When t0 is taken over all the time t of the injection process, the gas cap pressure p of the whole process can be obtainedk (t).

[0119] In an optional embodiment, the oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure, including:

[0120] Based on the gas cap pressure and the first relation, the depth of the oil-gas interface is obtained;

[0121] Calculate the oil pressure according to the depth of the oil-gas interface;

[0122] The bottom hole pressure is calculated based on the gas cap pressure and oil body pressure.

[0123] In an optional embodiment, calculating the oil pressure according to the oil-gas interface depth includes:

[0124] The oil body height is calculated based on the total depth of the salt cavern oil reservoir and the depth of the oil-gas interface:

[0125] h=H-(Hh)

[0126] Among them, H is the total depth of the salt cavern oil reservoir, and Hh is the depth of the oil-gas interface;

[0127] The oil pressure is calculated based on the oil height:

[0128]

[0129] Among them, p i (t) is the oil pressure; ρ o is the density of crude oil; c is the compression coefficient of crude oil, g is the acceleration of gravity, g = 9.8m / s 2 .

[0130] In an optional embodiment, calculating the bottom hole pressure according to the gas cap pressure and the oil body pressure includes:

[0131] Add the gas cap pressure and the oil body pressure to obtain the bottom hole pressure:

[0132] p w (t) = p k (t)+p i (t) (11)

[0133] Among them, p k (t) is the gas cap pressure, p i (t) is the oil pressure, p w (t) is the bottom hole pressure.

[0134] Bottom hole pressure p w (t) consists of two parts, including: gas cap pressure p k(t): As the oil-gas interface changes, the pressure exerted by the gas cap will continue to increase, reflecting the compression of the gas in the salt cavern; the oil body pressure p i (t): The volume change of the oil body itself increases with the change of the oil injection amount, thereby affecting the pressure of the oil body.

[0135] As a first example, Figure 4 As shown in the figure, taking a salt cave in Jintan as an example, its specific parameters are as follows: oil density ρ is 851kg / m 3 The relationship between the oil volume coefficient and pressure is shown in Table 1. The total height of the salt cavern is 140m. The top 20m of the salt cavern is approximately cylindrical with a radius of 19.5m. The middle 40m is approximately cylindrical with a radius of 35m. The bottom is considered to be a cylindrical shape with a height of 80m and a radius of 54.5m. The gravity acceleration g is 9.8m / s 2 , the initial oil level h0 is 0m, and the injection speed q is 2000m 3 / d, original pressure of salt cavern gas p k0 It is 2.5MPa. In the embodiment of the present application, a pressure sensor is installed at the bottom of the injection well (located at the bottom of the salt cavern oil storage tank). During the injection process, the bottom hole pressure is tested once every month. After 340 days of injection, the bottom hole pressure is monitored to be 39.37MPa, and the rock limit (rock fracture) pressure is 40MPa.

[0136] The volume coefficient B value of crude oil is:

[0137] Pressure p / MPa Volume coefficient B 0.1 1.01 1 1.03 2 1.07 5 1.15 10 1.39 13 1.38 15 1.37 20 1.36

[0138] According to the steps described in steps 101-104, the measured pressure data of the injection process is fitted and analyzed, such as Figure 5 As shown. Among them, the test pressure is the test data of the bottom hole pressure sensor every month during the injection process, and the calculated pressure is the pressure data calculated by the method proposed in the embodiment of the present application. Among them, the solid line is the calculated pressure under the safe operation conditions of the oil storage tank, that is, the calculated pressure within the safety range, and the dotted line is the predicted pressure that exceeds the safe operation pressure and does not reach the limit pressure (rock fracturing pressure) condition, that is, the predicted pressure beyond the safety range. The fitting error between the calculated pressure and the test pressure is 3.57%, indicating that the calculation method provided in the embodiment of the present application is consistent with the actual test results. The results show that: with the increase of injection time, the bottom hole pressure continues to increase; when it is close to 299 days, the volume coefficient B of crude oil reaches its maximum value, and then begins to decrease. That is: the rising slope of the bottom hole pressure reaches its maximum value when it is close to 299 days, and then decreases.

[0139] According to formula (9), the change of gas cap pressure under different injection time is calculated, as follows: Figure 6At 299 days, the volume coefficient reached its maximum value, and the rising slope of the gas cap pressure curve reached its maximum value, and then began to decrease. During the final safe operation period, the maximum gas cap pressure was 38.45MPa.

[0140] The gas head pressure p k The result of (t) is put into formula (7) to obtain the oil-gas interface depth Hh(t) at different injection times, as follows: Figure 7 Among them, the oil-gas interface depth within the safety range is calculated based on the gas cap pressure and volume compression coefficient that can be carried within the safety range of the salt cavern; the oil-gas interface depth beyond the safety range is calculated based on the gas cap pressure of the salt cavern oil reservoir between the risk of salt cavern occurrence and the volume compression coefficient.

[0141] according to Figure 5-7 It can be seen that at 292 days of injection, the bottom hole pressure was 13.62MPa and the gas cap pressure was 12.95MPa. At this time, the oil-gas interface depth was 60.06m, and the oil surface began to enter the middle cavity. At 299 days of injection, the bottom hole pressure was 18.09MPa and the gas cap pressure was 17.33MPa. At this time, the oil-gas interface depth was 48.45m, and the oil phase volume coefficient was the largest. At 340 days of injection, the bottom hole pressure was 39.37MPa and the gas cap pressure was 38.45MPa. At this time, the oil-gas interface depth was 29.41m. The gas cap pressure and bottom hole pressure exceeded the safety range, and the injection needed to be stopped.

[0142] Based on the same principle as the method provided in the embodiment of the present application, the embodiment of the present application also provides a system for determining the oil-gas interface of a salt cavern oil reservoir, such as Figure 8 As shown, the system includes:

[0143] A mathematical model building module 801 is used to determine a first relationship between the gas cap pressure and the oil body height before and after the oil injection process based on a real gas state equation;

[0144] The mathematical model building module 801 is also used to determine a second relationship based on the relationship between the oil-gas interface depth and the injection time;

[0145] A data acquisition module 802 is used to obtain the gas cap pressure based on the first relationship and the second relationship;

[0146] The data acquisition module 802 is also used to obtain the oil-gas interface depth, oil body pressure and bottom hole pressure according to the gas cap pressure.

[0147] In the embodiment of the present application, based on the real gas state equation, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process is determined; the second relationship between the oil-gas interface depth and the injection time is determined, and then the gas cap pressure is obtained based on the first relationship and the second relationship, and the oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure. The system in the embodiment of the present application can accurately monitor the changes in the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, obtain oil surface parameters, and thus effectively judge the depth changes of the oil-gas interface, and provide reliable data support for the oil and gas distribution and injection process of the salt cavern oil reservoir, and the monitoring cost is low. The system can also monitor the gas cap pressure and oil body pressure of the salt cavern oil reservoir in real time, and can more safely and intuitively understand the leakage problems that may occur inside the salt cavern.

[0148] In an optional embodiment, the system further comprises a plurality of groups of optical fiber sensors and acoustic wave sensors arranged on the side wall of the salt cavern oil storage depot, for monitoring whether there are cracks in the wall.

[0149] The system for determining the oil-gas interface of a salt cavern oil reservoir provided in the embodiment of the present application can achieve Figures 1 to 7 To avoid repetition, the various processes implemented in the method embodiment are not described here.

[0150] The system for determining the oil-gas interface of a salt cavern oil reservoir in the embodiment of the present application can execute the method for determining the oil-gas interface of a salt cavern oil reservoir provided in the embodiment of the present application, and its implementation principle is similar. The actions performed by each module and unit in the system for determining the oil-gas interface of a salt cavern oil reservoir in each embodiment of the present application correspond to the steps in the method for determining the oil-gas interface of a salt cavern oil reservoir in each embodiment of the present application. For the detailed functional description of each module of the system for determining the oil-gas interface of a salt cavern oil reservoir, please refer to the description in the corresponding method for determining the oil-gas interface of a salt cavern oil reservoir shown in the previous text, which will not be repeated here.

[0151] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above disclosed concept. For example, the above features are replaced with the technical features with similar functions disclosed in this application (but not limited to) by each other to form a technical solution.

Claims

1. A method for determining the oil-gas interface of a salt cavern oil reservoir, characterized in that: The method comprises: Based on the real gas state equation, the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process is determined; Determine the second relationship between the oil-gas interface depth and the injection time; Obtaining the gas cap pressure by solving the first relational expression and the second relational expression; The oil-gas interface depth, oil body pressure and bottom hole pressure are obtained according to the gas cap pressure.

2. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 1, characterized in that: The first relation is: Among them, p k (t) is the gas cap pressure; t is the injection time; H is the total depth of the salt cavern oil reservoir; p k0 is the initial pressure of the gas cap; h is the height of the oil body, Hh is the depth of the oil-gas interface; z is the altitude coordinate of the corresponding depth; r is the radius corresponding to the depth z.

3. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 2, characterized in that: The second relationship between the oil-gas interface depth and the injection time includes: The surface injection volume qt is calculated by the volume coefficient B and the gas cap pressure p k After conversion of (t), the effective volume in the salt cavern oil storage tank is qtB(p k (t)); The relationship between the oil-gas interface depth and the injection time is expressed by the change relationship between the oil phase volume and the oil-gas interface depth, and the second relationship is determined: Where q is the injection speed.

4. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 3, characterized in that: The obtaining the gas cap pressure by solving the first relational expression and the second relational expression comprises: The coordinate transformation of the first relational expression yields: After finishing, we can get: Then transform the integral interval of formula (4) to obtain: After finishing, we get: The coordinate transformation of the second relational expression is: Substituting formula (6) into formula (7) yields: When a certain time t0 is given, the unknown quantity p k (t0) is a certain value, recorded as x, then the solution equation is determined: For the solution equation, the iterative x solution is used to calculate the gas cap pressure p at any time t0 k (t0).

5. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 4, characterized in that: For the solution equation, the iterative x solution is used to calculate the gas cap pressure p at any time t0 k (t0), including: Determine the time t0=t(k) of this iteration; where k represents the current iteration number, and k=1 for the initial iteration; Calculate the current iteration time, x0(t0) = p k (t); If the absolute value of F(x0) is less than e, calculate and output p k (t) = x0, otherwise x0 = x0 + Δp, and re-determine whether the absolute value of F(x0) is less than e.

6. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 4, characterized in that: The step of obtaining the oil-gas interface depth, oil body pressure and bottom hole pressure according to the gas cap pressure comprises: Based on the gas cap pressure and the first relationship, obtaining the oil-gas interface depth; Calculating the oil body pressure according to the oil-gas interface depth; The bottom hole pressure is calculated according to the gas cap pressure and the oil body pressure.

7. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 6, characterized in that: The calculating the oil body pressure according to the oil-gas interface depth comprises: The oil body height is calculated based on the total depth of the salt cavern oil reservoir and the oil-gas interface depth: h=H-(Hh) Among them, H is the total depth of the salt cavern oil reservoir, and Hh is the depth of the oil-gas interface; The oil body pressure is obtained by calculating the oil body height: Among them, p i (t) is the oil pressure; ρ o is the density of crude oil; c is the compression coefficient of crude oil, and g is the acceleration of gravity.

8. The method for determining the oil-gas interface of a salt cavern oil storage depot according to claim 1 or 7, characterized in that: The calculating the bottom hole pressure according to the gas cap pressure and the oil body pressure comprises: The gas cap pressure and the oil body pressure are added to obtain the bottom hole pressure: p w (t)=p k (t)+p i (t) (11) Among them, p k (t) is the gas cap pressure, p i (t) is the oil pressure, p w (t) is the bottom hole pressure.

9. A system for determining the oil-gas interface of a salt cavern oil reservoir, characterized in that: The system comprises: A mathematical model building module, used to determine the first relationship between the gas cap pressure and the oil-gas interface depth before and after the oil injection process based on the real gas state equation; The mathematical model building module is also used to determine a second relationship between the oil-gas interface depth and the injection time; A data acquisition module, configured to obtain the gas cap pressure by solving the first relational expression and the second relational expression; The data acquisition module is also used to obtain the oil-gas interface depth, oil body pressure and bottom hole pressure according to the gas cap pressure.

10. The system for determining the oil-gas interface of a salt cavern oil storage depot according to claim 1, characterized in that: The system also includes a plurality of groups of optical fiber sensors and acoustic wave sensors arranged on the side walls of the salt cavern oil storage depot.

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