Deepwater gas reservoir dynamic reserve calculation method

Abstract

The invention relates to the technical field of natural gas development, in particular to a deep water gas reservoir dynamic reserve calculation method, which comprises the following steps of: acquiring basic information of a target well; establishing a deep water gas reservoir dynamic reserve calculation equation; correcting a deep water gas reservoir dynamic reserve calculation equation; and solving the corrected deep water gas reservoir dynamic reserve calculation equation. According to the method, the dynamic reserves calculation equation of the deepwater gas reservoir is obtained by establishing the material balance equation of the limited closed water body, and the complex phase state change existing in the development of the deepwater gas reservoir is further considered; the deep water gas reservoir dynamic reserve calculation equation is corrected from the five aspects of condensate water, reverse condensation, water-soluble gas, rock skeleton expansion and formation water invasion, after the corrected deep water gas reservoir dynamic reserve calculation equation is obtained, the corrected deep water gas reservoir dynamic reserve calculation equation is solved, and calculation of the deep water gas reservoir dynamic reserve can be more accurate.

Description

Technical Field

[0001] The present invention relates to the technical field of natural gas development, and more specifically, to a method for calculating the dynamic reserves of deepwater gas reservoirs. Background Art

[0002] Dynamic reserves refer to the total amount of natural gas that can be produced when all production wells produce to zero pressure drop on the basis of the existing mining technology and methods. There are many existing methods for determining dynamic reserves. According to their different calculation principles, they can be summarized into three main categories: the first is to calculate dynamic reserves based on the material balance principle using static pressure data; the second is to calculate dynamic reserves based on the gas seepage law using flow pressure data; the third is to predict the change of gas well production based on the production law of gas reservoirs to estimate dynamic reserves. The first method is relatively simple to calculate and has high accuracy. It requires shutting in the well until the formation returns to static pressure. Deepwater gas reservoirs are subject to development costs, and the physical properties of gas reservoirs are generally good. The time for the formation pressure to return to static pressure is short, so it is more practical. The second method is relatively complex to calculate and generally uses commercial software. At the same time, it also requires a clear understanding of the formation permeability, reservoir distribution and heterogeneity, gas well skin coefficient, etc., in order to reasonably select the model and avoid multiple solutions. The third method is highly dependent on the production law. It has a good effect on the ideal homogeneous gas reservoir entering the decline period. When applied to actual gas reservoirs, the error is sometimes large.

[0003] From the perspective of calculation principle and convenience, the material balance method is highly applicable to deepwater gas reservoirs. However, there is another difficulty in determining the dynamic reserves of deepwater gas reservoirs. Deepwater gas reservoirs are generally developed in a unique way of underwater wellheads combined with sea pipes in series. The sea pipes are surrounded by seawater on the seabed, and the gas reservoir fluid needs to be transported through long-distance sea pipes to reach the platform. The fluid is affected by large changes in environmental temperature and pressure, and there is a certain gap between the platform's metering data and the gas reservoir environment, resulting in large calculation errors in the dynamic reserves of deepwater gas reservoirs. Summary of the invention

[0004] The purpose of the present invention is to overcome the disadvantage of large calculation error of dynamic reserves of deep-water gas reservoirs in the prior art, and to provide a method for calculating dynamic reserves of deep-water gas reservoirs, which can make the calculation of dynamic reserves of deep-water gas reservoirs more accurate.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for calculating the dynamic reserves of a deepwater gas reservoir is provided, comprising the following steps:

[0007] Obtaining basic information of target wells: Obtaining field data and experimental data of target wells;

[0008] Establish the dynamic reserve calculation equation of deep-water gas reservoirs: establish the dynamic reserve calculation equation of deep-water gas reservoirs through the material balance equation of limited closed water body;

[0009] Modifying the dynamic reserve calculation equation of the deepwater gas reservoir: considering the influence of condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion on the deepwater gas reservoir, the dynamic reserve calculation equation of the deepwater gas reservoir is modified to obtain a modified dynamic reserve calculation equation of the deepwater gas reservoir;

[0010] Solving the revised deepwater gas reservoir dynamic reserve calculation equation: solving the revised deepwater gas reservoir dynamic reserve calculation equation through the field data and the experimental data to obtain the deepwater gas reservoir dynamic reserves.

[0011] The method for calculating the dynamic reserves of deepwater gas reservoirs of the present invention aims at the characteristics that deepwater gas reservoirs are affected by changes in environmental pressure stabilization and there is a certain gap between the metering data of the platform and the gas reservoir environment. The method is improved on the basis of the traditional material balance method, and a material balance equation for a limited closed water body is established to obtain a dynamic reserve calculation equation for deepwater gas reservoirs. The method further considers the complex phase changes existing in the development of deepwater gas reservoirs, and corrects the dynamic reserve calculation equation for deepwater gas reservoirs from five aspects: condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion. After obtaining the corrected dynamic reserve calculation equation for deepwater gas reservoirs, the corrected dynamic reserve calculation equation for deepwater gas reservoirs is solved, so that the calculation of the dynamic reserves of deepwater gas reservoirs can be more accurate.

[0012] Preferably, the field data specifically include wellhead natural gas output, pressure under standard conditions, temperature under standard conditions, pressure under original gas reservoir conditions, temperature under original gas reservoir conditions, pressure under current gas reservoir conditions, and temperature under current gas reservoir conditions.

[0013] Preferably, the experimental data specifically include water body multiples, salt content in produced water, volume coefficient of natural gas in the gas reservoir under original state, volume coefficient of natural gas in the gas reservoir under current state, deviation factor under standard conditions, deviation factor under original gas reservoir conditions, deviation factor under current gas reservoir conditions, rock pore volume compression coefficient, formation water compression coefficient, formation water volume coefficient, bound water saturation and the volume of formation water produced in the gas reservoir excluding condensate water.

[0014] Preferably, the dynamic reserve calculation equation of the deepwater gas reservoir is specifically:

[0015]

[0016] Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G p is the natural gas output of the gas reservoir, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; V gis the pore volume occupied by the remaining gas in the current state, in m 3 ; B g It is the volume coefficient of natural gas in the gas reservoir under the current state and is dimensionless.

[0017] Preferably, the modified deepwater gas reservoir dynamic reserves calculation equation is specifically:

[0018]

[0019] Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; G g is the wellhead natural gas output, in m 3 ; G w is the volume change caused by condensate water, in m 3 ; B g V is the volume coefficient of natural gas in the gas reservoir at present, dimensionless; gi is the pore volume occupied by the residual gas in the original state, in m 3 ; ΔV p is the volume change caused by the expansion of the rock skeleton, in m 3 ; ΔV w is the volume change caused by formation water intrusion, in m 3 ; ΔV gw is the volume change caused by dissolved gas in water, in m 3 ; ΔV go is the volume change due to retrograde condensation, in m 3 .

[0020] Preferably, the relationship between the gas reservoir volume and production and the state equation under the original gas reservoir state are introduced to simplify the modified deepwater gas reservoir dynamic reserve calculation equation, and the following formula is specifically used for simplification:

[0021]

[0022] The simplest dynamic reserve calculation equation for deepwater gas reservoirs is obtained, which is:

[0023]

[0024] Among them, B gi is the volume coefficient of natural gas in the reservoir under the original state, dimensionless; p sc is the pressure under standard conditions, in MPa; Z sc is the deviation factor under standard conditions, dimensionless; T sc is the temperature under standard conditions, in K; p iis the pressure under the original gas reservoir conditions, in MPa; Z i is the deviation factor under the original gas reservoir conditions, dimensionless; T i is the temperature under the original gas reservoir conditions, in K; p is the pressure under the current gas reservoir conditions, in MPa; Z is the deviation factor under the current gas reservoir conditions, dimensionless; T is the temperature under the current gas reservoir conditions, in K.

[0025] Preferably, the simplest deepwater gas reservoir dynamic reserve calculation equation is solved using a trial and error method and a graphical method. The specific process is:

[0026] Step 1: Replace the parameters of the simplest deepwater gas reservoir dynamic reserves calculation equation, specifically:

[0027]

[0028] Among them, A, B and C are constants;

[0029] Step 2: Assume G, solve formula (2) and obtain the values ​​of A, B and C;

[0030] Step 3: Take A as the vertical coordinate, G g +G w As the horizontal axis, make a graph of formula (1);

[0031] Step 4: The value of the intersection of the graph of formula (1) and the horizontal axis is G';

[0032] Step 5: When G is not equal to G', assign the value of G' to G, and start the cycle from step 2 until G is equal to G'. This G is the solution of the simplest deepwater gas reservoir dynamic reserve calculation equation. By using the trial and error method and the graphical method to solve the simplest deepwater gas reservoir dynamic reserve calculation equation, the deepwater gas reservoir dynamic reserve can be calculated more conveniently and intuitively.

[0033] Preferably, the volume change caused by condensed water is calculated using the following formula:

[0034]

[0035] Among them, G w is the volume change caused by condensate water, in m 3 ; G g is the wellhead natural gas output, in m 3 ; R wgr is the condensate water-gas ratio, in m 3 / 10 4 m 3 ; B wis the correction coefficient, dimensionless; p is the pressure under the current gas reservoir conditions, in MPa; T is the temperature under the current gas reservoir conditions, in K; f sc is the salt content correction coefficient, dimensionless; σ is the salt content in the produced water, in %; C and D are constants. The correction coefficient is used to correct the volume change caused by condensate water, so that the calculation results of the dynamic reserves of deep-water gas reservoirs are more in line with the actual situation, thereby making the calculation of the dynamic reserves of deep-water gas reservoirs more accurate.

[0036] Preferably, the volume change caused by the expansion of the rock skeleton is calculated using the following formula:

[0037]

[0038] Where, ΔV p is the volume change caused by the expansion of the rock skeleton, in m 3 ; V p is the pore volume of the gas reservoir, in m 3 ;c p is the rock pore volume compression coefficient, in MPa -1 ; Δp is the gas reservoir pressure drop, in MPa; G is the dynamic reserves of deepwater gas reservoir, in m 3 ; S wi is the bound water saturation, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa.

[0039] Preferably, the volume change caused by formation water intrusion is calculated using the following formula:

[0040]

[0041] Where, ΔV w is the volume change caused by formation water intrusion, in m 3 ; V w is the volume of formation water in the gas reservoir, in m 3 ;c w is the formation water compressibility coefficient, in MPa -1 ; Δp is the reservoir pressure drop, in MPa; W p is the volume of formation water produced in the gas reservoir (excluding condensate water), in m 3 ; B w V is the formation water volume coefficient, dimensionless; pg is the pore volume of the gas zone in the gas reservoir, in m 3 ; S wi V is the bound water saturation, dimensionless; pwis the pore volume of the water zone in the gas reservoir, in m 3 ; N is the water body multiple, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa; V p is the pore volume of the gas reservoir, in m 3 ; G is the dynamic reserves of deepwater gas reservoirs, in m 3 .

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. A method for calculating the dynamic reserves of deepwater gas reservoirs of the present invention is based on the traditional material balance method, aiming at the fact that deepwater gas reservoirs are affected by changes in environmental pressure stabilization and there is a certain gap between the metering data of the platform and the gas reservoir environment. The material balance equation of a limited closed water body is established to obtain a dynamic reserve calculation equation for deepwater gas reservoirs. The method further considers the complex phase changes existing in the development of deepwater gas reservoirs, and corrects the dynamic reserve calculation equation for deepwater gas reservoirs from five aspects, namely, condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion. After obtaining the corrected dynamic reserve calculation equation for deepwater gas reservoirs, the corrected dynamic reserve calculation equation for deepwater gas reservoirs is solved, so that the calculation of the dynamic reserves of deepwater gas reservoirs can be more accurate.

[0044] 2. A method for calculating the dynamic reserves of a deepwater gas reservoir of the present invention can calculate the dynamic reserves of a deepwater gas reservoir more conveniently and intuitively by solving the simplest dynamic reserves calculation equation of a deepwater gas reservoir using a trial and error method and a graphical method. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a flow chart of the method for calculating the dynamic reserves of deepwater gas reservoirs;

[0046] Figure 2 It is a schematic diagram of solving the dynamic reserves of deep-water gas reservoirs in Example 4. DETAILED DESCRIPTION

[0047] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0048] Embodiment 1

[0049] This embodiment is a first embodiment of a method for calculating dynamic reserves of a deepwater gas reservoir. Figure 1 As shown, the following steps are included:

[0050] Obtaining basic information of target wells: Obtaining field data and experimental data of target wells;

[0051] Establishment of dynamic reserve calculation equation for deepwater gas reservoirs: The dynamic reserve calculation equation for deepwater gas reservoirs is established through the material balance equation for finite closed water bodies; the dynamic reserve calculation equation for deepwater gas reservoirs is an improvement on the traditional material balance equation, and the material balance equation is established from the aspect of phase changes in finite closed water bodies.

[0052] Modification of the dynamic reserve calculation equation for deepwater gas reservoirs: The dynamic reserve calculation equation for deepwater gas reservoirs is modified by considering the effects of condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion on deepwater gas reservoirs to obtain the modified dynamic reserve calculation equation for deepwater gas reservoirs; this correction mainly considers the result deviation caused by the phase changes of natural gas due to condensate water, retrograde condensate and water-soluble gas.

[0053] Solve the revised deepwater gas reservoir dynamic reserves calculation equation: Solve the revised deepwater gas reservoir dynamic reserves calculation equation through field data and experimental data to obtain the deepwater gas reservoir dynamic reserves.

[0054] The working principle of a method for calculating dynamic reserves of a deepwater gas reservoir in this embodiment is as follows:

[0055] The present invention is mainly applicable to deepwater gas reservoirs with limited closed water bodies and complex phase changes. In view of the fact that deepwater gas reservoirs are affected by changes in environmental pressure stabilization and there is a certain gap between the metering data of the platform and the gas reservoir environment, improvements are made on the basis of the traditional material balance method, a material balance equation for limited closed water bodies is established, and a dynamic reserve calculation equation for deepwater gas reservoirs is obtained. The complex phase changes existing in the development of deepwater gas reservoirs are further considered, and the dynamic reserve calculation equation for deepwater gas reservoirs is corrected from five aspects: condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion. After the corrected dynamic reserve calculation equation for deepwater gas reservoirs is obtained, the corrected dynamic reserve calculation equation for deepwater gas reservoirs is solved, so that the calculation of the dynamic reserves of deepwater gas reservoirs can be more accurate.

[0056] Embodiment 2

[0057] The present embodiment proposes a method for calculating the dynamic reserves of deepwater gas reservoirs. Based on the first embodiment, in the present embodiment, the field data specifically include the wellhead natural gas output, the pressure under standard conditions, the temperature under standard conditions, the pressure under original gas reservoir conditions, the temperature under original gas reservoir conditions, the pressure under current gas reservoir conditions, and the temperature under current gas reservoir conditions; the original gas reservoir conditions are the conditions before the oil and gas fields are exploited, and the current gas reservoir conditions are the conditions when measured after exploitation.

[0058] The specific steps for obtaining the field data of the target well are as follows: close the target well and allow the formation to return to static pressure. This step can ensure that each measurement of the field data is carried out under the same pressure state, which can improve the accuracy of the dynamic reserves of deep-water gas reservoirs; measure at the target well through measuring equipment, that is, measure at the oil and gas field production site through a series of technical means such as fluid meters, well logging, geophysics, etc.; and obtain field data.

[0059] The experimental data specifically include water body multiples, salt content in produced water, natural gas volume coefficient in the gas reservoir under original conditions, natural gas volume coefficient in the gas reservoir under current conditions, deviation factor under standard conditions, deviation factor under original gas reservoir conditions, deviation factor under current gas reservoir conditions, rock pore volume compression coefficient, formation water compression coefficient, formation water volume coefficient, irreducible water saturation, and the volume of formation water produced in the gas reservoir (excluding condensate water);

[0060] Acquire the experimental data of the target well. The experimental data referred to in this embodiment are mainly parameters that cannot be directly measured and provided at the oil and gas field production site, and need to be obtained by using experiments and related calculation formulas. The specific steps are: collect the material of the target well; use experimental equipment to analyze the material, mainly to analyze and calculate the measured gas components; and obtain experimental data.

[0061] The dynamic reserve calculation equation of the deepwater gas reservoir is specifically:

[0062]

[0063] Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G p is the natural gas output of the gas reservoir, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; V g is the pore volume occupied by the remaining gas in the current state, in m 3 ; B g It is the volume coefficient of natural gas in the gas reservoir under the current state and is dimensionless.

[0064] The revised dynamic reserve calculation equation for deepwater gas reservoirs is:

[0065]

[0066] Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; G g is the wellhead natural gas output, in m 3 ; Gw is the volume change caused by condensate water, in m 3 ; B g V is the volume coefficient of natural gas in the gas reservoir at present, dimensionless; gi is the pore volume occupied by the residual gas in the original state, in m 3 ; ΔV p is the volume change caused by the expansion of the rock skeleton, in m 3 ; ΔV w is the volume change caused by formation water intrusion, in m 3 ; ΔV gw is the volume change caused by dissolved gas in water, in m 3 ; ΔV go is the volume change due to retrograde condensation, in m 3 .

[0067] The relationship between gas reservoir volume and production and the state equation under the original gas reservoir state are introduced to simplify the dynamic reserve calculation equation of the revised deepwater gas reservoir. The following formula is used for simplification:

[0068]

[0069] The simplest dynamic reserve calculation equation for deepwater gas reservoirs is obtained, which is:

[0070]

[0071] Among them, B gi is the volume coefficient of natural gas in the reservoir under the original state, dimensionless; p sc is the pressure under standard conditions, in MPa; Z sc is the deviation factor under standard conditions, dimensionless; T sc is the temperature under standard conditions, in K; p i is the pressure under the original gas reservoir conditions, in MPa; Z i is the deviation factor under the original gas reservoir conditions, dimensionless; T i is the temperature under the original gas reservoir conditions, in K; p is the pressure under the current gas reservoir conditions, in MPa; Z is the deviation factor under the current gas reservoir conditions, dimensionless; T is the temperature under the current gas reservoir conditions, in K.

[0072] To obtain the volume change caused by condensate water due to phase change during the production of formation natural gas, the source of water production in the gas well can be analyzed, and the production of condensate water can be converted to the volume under the temperature and pressure conditions of the gas reservoir. There are many methods to determine the condensate water content of natural gas, such as experimental measurement, chart determination, state equation calculation and empirical formula method. Experimental measurement is time-consuming and costly; chart reference is cumbersome and prone to human errors; state equation calculation is based on the oil, gas and water multiphase equilibrium theory and the principle of fluid thermodynamic equilibrium, and the calculation process is complicated; empirical formulas are mostly obtained by regression based on measured data. Although the calculation is simple and convenient, the use of empirical formulas is limited due to the large differences in natural gas components in different regions. Based on the characteristics of the above methods, the present invention regresses the empirical formula based on experimental data on a certain experimental basis. If there are no experimental conditions, the appropriate formula can be selected based on the characteristics of the natural gas components in the gas reservoir. In this embodiment, the volume change caused by condensate water is specifically calculated using the following formula:

[0073]

[0074] Among them, G w is the volume change caused by condensate water, in m 3 ; G g is the wellhead natural gas output, in m 3 ; R wgr is the condensate water-gas ratio, in m 3 / 10 4 m 3 ; B w is the correction coefficient, dimensionless; p is the pressure under the current gas reservoir conditions, in MPa; T is the temperature under the current gas reservoir conditions, in K; f sc is the salt content correction coefficient, dimensionless; σ is the salt content in the produced water, in %, produced water is water produced in addition to condensate water, including formation water and movable water; C and D are constants. The correction coefficient is calculated based on the actual situation, that is, the water-gas ratio data in the early stage of actual production, when the water-gas ratio is stable and the chloride content is low, is simulated and calculated, and the calculated value is compared with the actual value. At the same time, by using this correction coefficient, the condensate water production can be converted to the temperature and pressure conditions of the gas reservoir. The correction coefficient is used to correct the volume change caused by condensate water, so that the calculation results of the dynamic reserves of deep-water gas reservoirs are more in line with the actual situation, so that the calculation of the dynamic reserves of deep-water gas reservoirs can be more accurate.

[0075] The volume change caused by the expansion of the rock skeleton is calculated using the following formula:

[0076]

[0077] Where, ΔV pis the volume change caused by the expansion of the rock skeleton, in m 3 ; V p is the pore volume of the gas reservoir, in m 3 ;c p is the rock pore volume compression coefficient, in MPa -1 ; Δp is the gas reservoir pressure drop, in MPa; G is the dynamic reserves of deepwater gas reservoir, in m 3 ; S wi is the bound water saturation, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa.

[0078] The volume change caused by formation water intrusion is calculated using the following formula:

[0079]

[0080] Where, ΔV w is the volume change caused by formation water intrusion, in m 3 ; V w is the volume of formation water in the gas reservoir, in m 3 ;c w is the formation water compressibility coefficient, in MPa -1 ; Δp is the reservoir pressure drop, in MPa; W p is the volume of formation water produced in the gas reservoir (excluding condensate water), in m 3 ; B w V is the formation water volume coefficient, dimensionless; pg is the pore volume of the gas zone in the gas reservoir, in m 3 ; S wi V is the bound water saturation, dimensionless; pw is the pore volume of the water zone in the gas reservoir, in m 3 ; N is the water body multiple, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa; V p is the pore volume of the gas reservoir, in m 3 ; G is the dynamic reserves of deepwater gas reservoirs, in m 3 .

[0081] Solving the release of dissolved natural gas in formation water is actually solving the phase equilibrium problem of gas and water. The theoretical basis of this problem is Henry's law, which is often corrected by the Krichevsky-Kasarnovsky equation under high pressure conditions. The volume change caused by water-soluble gas is calculated using the state equation method, which is mainly based on the pressure stability of the gas reservoir, the composition of water and the composition of gas. In actual use, due to different temperature and pressure conditions, different gas components, and different properties of formation water, the application effect of the state equation is also quite different. When the calculated value differs too much from the experimental value, it is necessary to replace the state equation or adjust the Henry constant to recalculate the dissolved amount of natural gas.

[0082] During the production process, the gas reservoir follows the law of gas seepage, and the pressure distribution around the gas well presents a funnel shape, that is, the pressure drop near the wellbore is large, and the pressure drop far from the wellbore is small. When the pressure drops below the dew point pressure, retrograde condensation will occur in the gas reservoir. The amount of retrograde condensation in the gas reservoir is closely related to the pressure distribution range. The volume change caused by retrograde condensation is calculated using the numerical simulation method. On the basis of the establishment of the component model, the production data is historically fitted to predict the distribution of formation pressure and the corresponding oil saturation during the production process, and the amount of condensate oil remaining in the gas reservoir is obtained.

[0083] After solving the above unknown quantities, the simplest deepwater gas reservoir dynamic reserve calculation equation is solved using the trial and error method and the graphical method. The specific process is as follows:

[0084] Step 1: Replace the parameters of the simplest deepwater gas reservoir dynamic reserves calculation equation, specifically:

[0085]

[0086] Among them, A, B and C are constants;

[0087] Step 2: Assume G, solve formula (2) and obtain the values ​​of A, B and C;

[0088] Step 3: Take A as the vertical coordinate, G g +G w As the horizontal axis, make a graph of formula (1);

[0089] Step 4: The value of the intersection of the graph of formula (1) and the horizontal axis is G';

[0090] Step 5: When G is not equal to G', assign the value of G' to G, and start the cycle from step 2 until G is equal to G'. This G is the solution of the simplest deepwater gas reservoir dynamic reserve calculation equation. By using the trial and error method and the graphical method to solve the simplest deepwater gas reservoir dynamic reserve calculation equation, the deepwater gas reservoir dynamic reserve can be calculated more conveniently and intuitively.

[0091] Embodiment 3

[0092] This embodiment is to apply the deepwater gas reservoir dynamic reserve calculation method to calculate the deepwater gas reservoir dynamic reserve of the A1 well located in the deepwater L gas field. On the basis of the first to third embodiments, in this embodiment, the gas reservoir is a lithologic structural gas reservoir with only one production well. The pressure under the original gas reservoir condition is 39.35 MPa, the water body multiple is 3.5 times, the bound water saturation is 0.257, and the rock pore volume compression coefficient is 9.16×10 -4 MPa -1 , the formation water compressibility coefficient is 5.10×10 -4 MPa -1 The deviation factor under the original gas reservoir conditions is 1.11, the correction coefficient is 1.02, the deviation factor under standard conditions is 0.99, and the temperature is 92.6℃. The specific test data of the well are shown in Table 1.

[0093] Table 1 Shut-in pressure measurement and corresponding production data

[0094]

[0095] Using the simplest deepwater gas reservoir dynamic reserve calculation equation, the trial and error method and the graphical method are used to solve it. Assuming the value of G, the equation 2 is solved to obtain the values ​​of A, B and C. With A as the ordinate, G g +G w The value is the horizontal axis, and the graph of formula 1 is made, such as Figure 2 As shown in the figure, the intersection of the graph of formula 1 and the horizontal axis is the value of G'; when the value of G is not equal to the value of G', the value of G' is assigned to G, and the cycle starts from step 2 until the value of G is equal to the value of G'. The value of G is the solution of the simplest deepwater gas reservoir dynamic reserve calculation equation. The dynamic reserve of the deepwater gas reservoir is calculated to be 125.99×10 4 m 3 .

[0096] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0097] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for calculating dynamic reserves of deepwater gas reservoirs, characterized in that: The following steps are involved: Obtaining basic information of target wells: Obtaining field data and experimental data of target wells; Establish the dynamic reserve calculation equation of deep-water gas reservoirs: establish the dynamic reserve calculation equation of deep-water gas reservoirs through the material balance equation of limited closed water body; Modifying the dynamic reserve calculation equation of the deepwater gas reservoir: considering the influence of condensate water, retrograde condensate, water-soluble gas, rock skeleton expansion and formation water intrusion on the deepwater gas reservoir, the dynamic reserve calculation equation of the deepwater gas reservoir is modified to obtain a modified dynamic reserve calculation equation of the deepwater gas reservoir; Solving the revised deepwater gas reservoir dynamic reserve calculation equation: solving the revised deepwater gas reservoir dynamic reserve calculation equation through the field data and the experimental data to obtain the deepwater gas reservoir dynamic reserves.

2. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 1, characterized in that: The field data specifically include wellhead natural gas output, pressure under standard conditions, temperature under standard conditions, pressure under original gas reservoir conditions, temperature under original gas reservoir conditions, pressure under current gas reservoir conditions, and temperature under current gas reservoir conditions.

3. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 2, characterized in that: The experimental data specifically include water body multiples, salt content in produced water, natural gas volume coefficient in the gas reservoir under original conditions, natural gas volume coefficient in the gas reservoir under current conditions, deviation factor under standard conditions, deviation factor under original gas reservoir conditions, deviation factor under current gas reservoir conditions, rock pore volume compression coefficient, formation water compression coefficient, formation water volume coefficient, bound water saturation, and the volume of formation water produced in the gas reservoir excluding condensate water.

4. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 3, characterized in that: The dynamic reserve calculation equation of the deepwater gas reservoir is specifically: Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G p is the natural gas output of the gas reservoir, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; V g is the pore volume occupied by the remaining gas in the current state, in m 3 ; B g It is the volume coefficient of natural gas in the gas reservoir under the current state and is dimensionless.

5. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 4, characterized in that: The modified deepwater gas reservoir dynamic reserve calculation equation is specifically: Where G is the dynamic reserves of deepwater gas reservoirs, in m 3 ; G res is the remaining amount of natural gas in the gas reservoir, in m 3 ; G g is the wellhead natural gas output, in m 3 ; G w is the volume change caused by condensate water, in m 3 ; B g V is the volume coefficient of natural gas in the gas reservoir at present, dimensionless; gi is the pore volume occupied by the residual gas in the original state, in m 3 ; ΔV p is the volume change caused by the expansion of the rock skeleton, in m 3 ; ΔV w is the volume change caused by formation water intrusion, in m 3 ; ΔV gw is the volume change caused by dissolved gas in water, in m 3 ; ΔV go is the volume change due to retrograde condensation, in m 3 .

6. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 5, characterized in that: The relationship between gas reservoir volume and production and the state equation under the original gas reservoir state are introduced to simplify the modified deepwater gas reservoir dynamic reserve calculation equation. Specifically, the following formula is used for simplification: The simplest dynamic reserve calculation equation for deepwater gas reservoirs is obtained, which is: Among them, B gi is the volume coefficient of natural gas in the reservoir under the original state, dimensionless; p sc is the pressure under standard conditions, in MPa; Z sc is the deviation factor under standard conditions, dimensionless; T sc is the temperature under standard conditions, in K; p i is the pressure under the original gas reservoir conditions, in MPa; Z i is the deviation factor under the original gas reservoir conditions, dimensionless; T i is the temperature under the original gas reservoir conditions, in K; p is the pressure under the current gas reservoir conditions, in MPa; Z is the deviation factor under the current gas reservoir conditions, dimensionless; T is the temperature under the current gas reservoir conditions, in K.

7. The method for calculating dynamic reserves of deepwater gas reservoirs according to claim 6, characterized in that: The simplest deepwater gas reservoir dynamic reserve calculation equation is solved using the trial and error method and the graphical method. The specific process is as follows: Step 1: Replace the parameters of the simplest deepwater gas reservoir dynamic reserves calculation equation, specifically: Among them, A, B and C are constants; Step 2: Assume G, solve formula (2) and obtain the values ​​of A, B and C; Step 3: Take A as the vertical coordinate, G g +G w As the horizontal axis, make a graph of formula (1); Step 4: The value of the intersection of the graph of formula (1) and the horizontal axis is G'; Step 5: When G is not equal to G', the value of G' is assigned to G, and the cycle is repeated from step 2 until G is equal to G'. This G is the solution to the simplest deepwater gas reservoir dynamic reserve calculation equation.

8. The method for calculating dynamic reserves of deepwater gas reservoirs according to any one of claims 5 to 7, characterized in that: The volume change caused by condensate water is specifically calculated using the following formula: Among them, G w is the volume change caused by condensate water, in m 3 ; G g is the wellhead natural gas output, in m 3 ; R wgr is the condensate water-gas ratio, in m 3 / 10 4 m 3 ; B w is the correction coefficient, dimensionless; p is the pressure under the current gas reservoir conditions, in MPa; T is the temperature under the current gas reservoir conditions, in K; f sc is the salt content correction coefficient, dimensionless; σ is the salt content in the produced water, in %; C and D are constants.

9. The method for calculating dynamic reserves of deepwater gas reservoirs according to any one of claims 5 to 7, characterized in that: The volume change caused by the expansion of the rock skeleton is calculated using the following formula: Where, ΔV p is the volume change caused by the expansion of the rock skeleton, in m 3 ; V p is the pore volume of the gas reservoir, in m 3 ;c p is the rock pore volume compression coefficient, in MPa -1 ; Δp is the gas reservoir pressure drop, in MPa; G is the dynamic reserves of deepwater gas reservoir, in m 3 ; S wi is the bound water saturation, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa.

10. The method for calculating dynamic reserves of deepwater gas reservoirs according to any one of claims 5 to 7, characterized in that: The volume change caused by formation water intrusion is specifically calculated using the following formula: Where, ΔV w is the volume change caused by formation water intrusion, in m 3 ; V w is the volume of formation water in the gas reservoir, in m 3 ;c w is the formation water compressibility coefficient, in MPa -1 ; Δp is the reservoir pressure drop, in MPa; W p is the volume of formation water produced in the gas reservoir (excluding condensate water), in m 3 ; B w V is the formation water volume coefficient, dimensionless; pg is the pore volume of the gas zone in the gas reservoir, in m 3 ; S wi V is the bound water saturation, dimensionless; pw is the pore volume of the water zone in the gas reservoir, in m 3 ; N is the water body multiple, dimensionless; p i is the pressure under the original gas reservoir conditions, in MPa; p is the pressure under the current gas reservoir conditions, in MPa; V p is the pore volume of the gas reservoir, in m 3 ; G is the dynamic reserves of deepwater gas reservoirs, in m 3 .

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