High-temperature and high-pressure buried hill gas reservoir preservation condition evaluation method

Abstract

The invention discloses a high-temperature and high-pressure buried hill gas reservoir preservation condition evaluation method. The method comprises the following steps that the diffusion coefficient, the loss distance and the concentration of each layer of an upper covering layer of a to-be-evaluated high-temperature and high-pressure buried hill gas reservoir are obtained; quantitatively evaluating the preservation conditions of the high-temperature and high-pressure buried hill structure to be evaluated according to the Fick's law to obtain the loss rate value of a typical structure, analyzing the correlation between the gas layer thickness of each structure and the loss rate, and determining the plane distribution characteristics of the preservation conditions; establishing a geologic model of the upper covering layer of the high-temperature and high-pressure buried hill gas reservoir to be evaluated; quantitatively evaluating the plane distribution characteristics of the preservation conditions of the high-temperature and high-pressure buried hill gas reservoir to be evaluated according to the Fick's law, determining the capping capability difference of a covering layer on the high-temperature and high-pressure buried hill to be evaluated, and further determining a favorable region or favorable target of the preservation conditions; the high-temperature and high-pressure buried hill gas reservoir preservation condition can be quantitatively evaluated, the evaluation result is reliable, and reliable reference value can be provided for exploitation of the type of reservoir.

Description

Technical Field

[0001] The invention relates to the field of gas reservoir preservation conditions, and in particular to a method for evaluating the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir. Background Art

[0002] In recent years, with the sharp decline in production in old oil fields, the problem of severe shortage of reserve reserves has become increasingly prominent. However, in order to find new reserves, buried hill oil and gas reservoirs have become an important exploration and development field in the field of petroleum geology at home and abroad to find new oil and gas fields, especially for high-temperature and high-pressure buried hills. There is currently no relevant evaluation method. Summary of the invention

[0003] In view of the above problems, the present invention provides a method for evaluating the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir, which can accurately and quantitatively evaluate the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir.

[0004] The technical solution of the present invention is:

[0005] A method for evaluating the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir comprises the following steps:

[0006] S1. Obtain the diffusion coefficient of the overburden layer on the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0007] S2. Determine the dissipation distance of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0008] S3. Determine the concentration of each layer of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0009] S4. Based on the data obtained in steps S1-S3, quantitatively evaluate the preservation conditions of the high-temperature and high-pressure buried hill structure to be evaluated according to Fick's law to obtain the dissipation rate value of the typical structure, analyze the correlation between the thickness of the gas layer of each structure and the dissipation rate, determine the upper limit of the dissipation rate value of the high-temperature and high-pressure buried hill to be evaluated, and determine the plane distribution characteristics of the preservation conditions of the buried hill gas reservoir in the area to be evaluated;

[0010] S5. Establish a geological model of the overburden of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0011] S6. Based on the data obtained in steps S1-S3 and the model established in step S5, quantitative evaluation is performed on the planar distribution characteristics of the preservation conditions of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated according to Fick's law, and the difference in the sealing capacity of the overburden layer on the high-temperature and high-pressure buried-hill to be evaluated is determined, thereby determining the favorable preservation condition area or favorable target.

[0012] In the step S1, the diffusion coefficient is obtained based on the porosity.

[0013] In step S2, the dissipation distance is determined by the burial depth of each cap layer of the buried hill gas reservoir and the water depth.

[0014] In step S3, the concentration is determined according to the temperature and pressure characteristics of each cap layer of the buried hill gas reservoir.

[0015] In step S5, the overlying stratum model of the buried-hill gas reservoir is established based on the reflection interfaces and lithological characteristics of each stratum overlying the high-temperature and high-pressure buried-hill gas reservoir to be evaluated.

[0016] In step S6, the favorable preservation condition area or favorable target is determined by calculating the loss rate of the upper covering layer of the buried hill group of the high-temperature and high-pressure buried hill to be evaluated according to Fick's theorem.

[0017] The beneficial effects of the present invention are:

[0018] By using Fick's law to determine the loss amount and loss intensity, the preservation conditions of high-temperature and high-pressure buried-hill gas reservoirs can be quantitatively evaluated. The evaluation results are reliable and can provide a reliable reference value for the exploitation of this type of reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of a method for evaluating preservation conditions of a high-temperature and high-pressure buried hill gas reservoir according to an embodiment of the present invention;

[0020] Figure 2 is a graph showing the relationship between the diffusion coefficient and the rock porosity according to an embodiment of the present invention;

[0021] Figure 3 It is a histogram of the loss rate of each buried hill drilling in the Songnan low uplift and the Lingnan low uplift in the Qiongdongnan Basin according to the embodiment of the present invention;

[0022] Figure 4 is a correlation analysis diagram for determining the upper limit value of the natural gas diffusion rate in the study area according to an embodiment of the present invention;

[0023] Figure 5a It is a geological model diagram of the stratigraphic framework of the Songnan low uplift in the Qiongdongnan Basin according to an embodiment of the present invention;

[0024] Figure 5b It is a geological model diagram of the stratigraphic framework of the Lingnan low uplift in the Qiongdongnan Basin according to an embodiment of the present invention;

[0025] Figure 6a It is a fitting diagram of formation pressure and burial depth of Songnan low uplift in Qiongdongnan Basin according to an embodiment of the present invention;

[0026] Figure 6b It is a fitting diagram of formation pressure and burial depth of the Lingnan low uplift in the Qiongdongnan Basin described in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0028] Example:

[0029] like Figure 1 - Figure 2 As shown, a method for evaluating the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir is characterized by comprising the following steps:

[0030] S1. Obtain the diffusion coefficient of the overburden layer on the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0031] The natural gas diffusion coefficient (D) is an evaluation parameter that describes the speed at which natural gas diffuses through rocks. The larger the value, the faster the natural gas diffusion rate, and vice versa.

[0032] The high-temperature and high-pressure buried-hill gas reservoirs to be evaluated belong to the same basin or a smaller study area than the basin level, so the gas reservoir types are similar, and the diffusion coefficient is mainly controlled by the pore size of the cap rock. For the same basin or a smaller study area, regardless of the lithology of the cap rock, the natural gas diffusion coefficient tends to increase gradually with the increase of the rock porosity. In some embodiments, the correlation analysis between core porosity and natural gas diffusion coefficient ( Figure 2 ), the mathematical regression method can be used to obtain the relationship between cap rock porosity and natural gas diffusion coefficient, and the calculation formula is as follows:

[0033] D = 9.03 × 10 -7 Φ 1.87

[0034] Where: D is the natural gas expansion coefficient, m 2 / s; Φ is the porosity of the cap rock, %.

[0035] If there is no measured data on core porosity and natural gas diffusion coefficient, an approximate calculation can be performed based on the natural gas diffusion coefficient fitting formula of other similar areas.

[0036] Sometimes, there are multiple sets of cap layers with different physical properties on the high temperature and high pressure buried hill. In order to study it more accurately and finely, the upper cover layer can be split into several cap layer units. According to the diffusion coefficient and thickness percentage of each cap layer unit, the comprehensive natural gas diffusion coefficient D of multiple sets of cap layers on the buried hill can be obtained. T .

[0037]

[0038] Where: D T is the comprehensive natural gas diffusion coefficient, m 2 / s; Z-diffusion and loss distance of natural gas, m; H i is the thickness of the i-th cap layer, m; D i is the natural gas diffusion coefficient of the i-th cap layer, m 2 / s.

[0039] S2. Determine the dissipation distance of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0040] Since natural gas diffuses from the gas reservoir to the seabed, the thickness of the overburden on the gas reservoir is taken as the natural gas diffusion loss distance Z (m).

[0041] Sometimes, drilling data are available for the structure to be evaluated, and the natural gas diffusion loss distance Z can be obtained from lithological logging data;

[0042] Sometimes, for the structure to be evaluated that has not yet been drilled, the natural gas diffusion loss distance Z can be obtained through seismic profiles;

[0043] Sometimes, for the structure to be evaluated, which has not yet been drilled, the natural gas diffusion loss distance Z can be obtained through seismic profiles.

[0044] S3. Determine the concentration of each layer of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0045] Since the diffusion medium of natural gas underground is formation water, the gas concentration in pore water plays a role in natural gas diffusion, and its size is mainly controlled by its depth, temperature and pressure conditions. Therefore, the natural gas concentration in different cap layers can be calculated according to the solubility formula of natural gas in formation water. The calculation formula is as follows:

[0046]

[0047] Where: K p =e -18.56+2133.68 / T ; φ i =0.35φ m ,in:

[0048] φ m =2.12963×10 -8 t 3 -1.257929×10 -6 t 2 +3.1639178×10 -5 t+9.696829×10 -3 ;

[0049] Where: C is the gas concentration of the gas reservoir, K p -Methane hydration equilibrium constant; φ i - effective interstitial degree of pore water, %; R - gas constant, 8.315 J / mol; T - temperature, K; t - temperature, °C; p - pressure, Pa; b m -Van der Waals volume of gas, 4.28×10-5m3 / mol; φ m - Maximum effective interstitial degree of pore water, %;

[0050] S4. Based on the data obtained in steps S1-S3, quantitatively evaluate the preservation conditions of the high-temperature and high-pressure buried hill structure to be evaluated according to Fick's law to obtain the dissipation rate value of the typical structure, analyze the correlation between the thickness of the gas layer of each structure and the dissipation rate, determine the upper limit of the dissipation rate value of the high-temperature and high-pressure buried hill to be evaluated, and determine the plane distribution characteristics of the preservation conditions of the buried hill gas reservoir in the area to be evaluated;

[0051] Based on Fick's law, the loss rate V 失 It can be deduced that the natural gas loss rate is related to the natural gas diffusion coefficient (D), the concentration difference between the high-temperature and high-pressure buried-hill gas reservoir and its overlying layer (C-C0), and the diffusion loss distance (Z). According to the key parameters obtained in steps S1-S3, the natural gas loss rate of the buried-hill structure can be calculated to obtain the typical structural loss rate value. Finally, the correlation analysis between the thickness of the gas layer in each structure in the study area and the loss rate is carried out to determine the upper limit of the loss rate in the study area, and provide an evaluation standard for the plane distribution characteristics of the preservation conditions of the buried-hill gas reservoir in the evaluation area. The calculation formula is as follows:

[0052]

[0053]

[0054] Where: Q 失一气 Diffusion loss of natural gas in reservoir, m 3 ; D - diffusion coefficient of natural gas in overlying strata, m 2 / s; t-natural gas diffusion time s; dc / dz-concentration gradient in the natural gas diffusion direction, m 3 / m 3 / m; C-gas concentration in gas reservoir, m 3 / m 3 ; C0 - gas concentration in the cap rock, m 3 / m 3 ; s-natural gas diffusion area m 2 ; Z-natural gas diffusion and loss distance, m; v 失一气 Diffusion loss rate of natural gas in reservoir, m 3 / m 2 ·Ma;

[0055] The loss rate value refers to the amount of natural gas diffusion loss through the cap layer per unit area per unit time, which comprehensively considers the porosity of the cap layer, natural gas diffusion coefficient, temperature, pressure and other parameters. Therefore, for high-temperature and high-pressure gas reservoirs and their overlying layers, the loss rate can better quantitatively evaluate the sealing performance of the cap layer for high-temperature and high-pressure buried-hill gas reservoirs.

[0056] S5. Establish a geological model of the overburden of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0057] The basis for establishing the overlying strata model of the buried-hill gas reservoir is the reflection interface and lithology characteristics of each stratum overlying the high-temperature and high-pressure buried-hill gas reservoir to be evaluated;

[0058] S6. Based on the data obtained in steps S1-S3 and the model established in step S5, quantitative evaluation is performed on the planar distribution characteristics of the preservation conditions of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated according to Fick's law, and the difference in the sealing capacity of the overburden layer on the high-temperature and high-pressure buried-hill to be evaluated is determined, thereby determining the favorable preservation condition area or favorable target.

[0059] According to the temperature, pressure and natural gas diffusion coefficient characteristics of different cap rocks in the area, the loss rate of the overlying layer in the low uplift (buried hill group) in the area is calculated based on Fick's theorem, and then the favorable preservation conditions or favorable targets can be selected on the plane.

[0060] Specifically, the temperature distribution characteristics of each cap layer in the study area can be calculated through the thermal gradient in the study area, as shown in the formula below; the pressure distribution characteristics of each cap layer in the study area can be fitted through the pressure data of each layer of all wells in the study area and the burial depth data to obtain the relationship between pressure and depth applicable to the area, and then the pressure distribution characteristics of each cap layer can be calculated according to the depth domain data of the seismic reflection surface of each cap layer in the study area; the natural gas diffusion coefficient distribution characteristics of each cap layer in the study area can be calculated through the logging porosity data of each formation of a single well in the area.

[0061] T=T gd ×d×10 -2 +T0

[0062] Where: T - formation temperature, °C; T gd -geothermal gradient, ℃ / 100m; d-burial depth, m; T 0－ Seafloor temperature, °C.

[0063] In some examples, the geophysical property inversion data can be used to obtain the natural gas diffusion coefficient distribution characteristics of each cap layer in the work area.

[0064] After obtaining the temperature, pressure and natural gas diffusion coefficient data of the upper covering layer of the high-temperature and high-pressure buried hill by the above method, each cover layer is taken as a calculation unit, and the temperature and pressure data are calculated "face to face" by formula 3 to obtain the natural gas concentration distribution characteristics of each layer, and the concentration difference between the buried hill gas reservoir and each cover layer is further calculated. The loss rate of the upper covering layer of the low uplift (buried hill group) in the area is obtained in combination with the natural gas diffusion coefficient calculation. Finally, the favorable preservation condition area or favorable target is evaluated according to the planar distribution characteristics of the loss rate and the upper limit of the loss rate determined in step S4. Specific embodiment:

[0066] This embodiment takes the Y8-1, Y8-3, Y10, Y13 structures of Songnan low uplift and the L26, L26, L32 structures of Lingnan low uplift as examples to introduce in detail the calculation of the loss rate value, the determination of the upper limit of the loss rate and the optimization of the favorable area.

[0067] (1) Obtaining the diffusion coefficient of the overburden layer of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated

[0068] The Y8-1 and Y8-3 structures in the Songnan Low Uplift each have two buried-hill wells, namely Y8-1a and Y8-1b, and Y8-3a and Y8-3b; the Y10 and Y13 structures already have corresponding buried-hill wells, namely Y10a and Y13a. The L26 and L32 structures in the Lingnan Low Uplift already have corresponding buried-hill wells, namely L26a and L32a. Based on the well logging porosity of the wells that have been drilled, the well logging porosity of the overburden layer on the buried hill is averaged to obtain the porosity value corresponding to each well. The natural gas diffusion coefficient corresponding to each cap layer is obtained through the porosity, and then the comprehensive diffusion coefficient D of each well is calculated. T The porosity and diffusion coefficient values ​​are detailed in Table 1.

[0069] Table 1 Statistics of drilling diffusion coefficients of typical structures in Songnan Low Uplift and Lingnan Low Uplift

[0070]

[0071] (2) Determine the dissipation distance of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated

[0072] Since this example is a marine buried hill natural gas reservoir, the divergence distance is the distance from the buried hill interface to the seabed of each well. The divergence distances of each well in Songnan Low Uplift and Lingnan Low Uplift are shown in Table 2.

[0073] Z=D b -D0

[0074] Where: Z - natural gas diffusion and loss distance, m; D b - burial depth of the buried top interface, m; D 0－ Water depth, m;

[0075] Table 2 Statistics of drilling loss distances of typical structures in Songnan Low Uplift and Lingnan Low Uplift

[0076]

[0077] (3) Determine the concentration of each layer of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated

[0078] In this embodiment, the temperature data of the buried hill reservoir and the upper cover layer of the typical structure of Songnan Low Uplift and Lingnan Low Uplift are obtained from the drilling logging data, the pressure data are obtained from the drilling pressure measurement data, and the concentration is calculated by Formula 3; for the cap rock natural gas concentration, since the natural gas is lost from the buried hill reservoir to the seabed, the Songnan Low Uplift is a normal pressure cap rock, and the cap rock concentration is the seabed natural gas concentration. From the logging temperature measurement data, it can be known that the seabed temperature is 4°C and the pressure is the hydrostatic pressure of 18Mpa. It can be calculated that the seabed natural gas concentration of the Songnan Low Uplift is 0.046225353m 3 / m 3 As for the high-pressure cap rock in Lingnan Low Uplift, the presence of abnormally high pressure and high temperature in the upper cover increases the concentration of natural gas in the cap rock, which can be calculated by Equation 3 based on the temperature and pressure conditions of the overlying direct cover rock. The detailed data of the buried hill reservoir and the upper cover rock of each well are shown in Table 3.

[0079] Table 3 Statistics of gas reservoir concentration in typical structural wells of Songnan Low Uplift and Lingnan Low Uplift

[0080]

[0081] (4) Based on the data obtained in steps S1-S3, the loss rate value of typical structural drilling is obtained according to Fick's law, and the correlation between the thickness of the gas layer in each structure in the study area and the loss rate is analyzed to determine the upper limit of the loss rate in the study area, thereby providing an evaluation standard for the plane distribution characteristics of the preservation conditions of the buried hill gas reservoir in the area to be evaluated;

[0082] ① The comprehensive diffusion coefficient D of the overburden on the typical structures of Songnan Low Uplift and Lingnan Low Uplift obtained from steps S1-S3 T , dissipation distance Z, concentration difference (C-C0) data, and the dissipation rate value of each well was calculated according to Fick's law (Formula 4-2). The detailed data on the dissipation rate of drilling wells in typical structures of Songnan Low Uplift and Lingnan Low Uplift are shown in Table 4.

[0083] like Figure 3 As shown in Figure 2, the dissipation rates of the Songnan low uplift and the Lingnan low uplift in the Qiongdongnan Basin are quite different, with the dissipation rate of the Songnan low uplift ranging from 4.91 to 13.38 m 3 / Ma*m 2 , with an average of 8.54m 3 / Ma*m 2 The Lingnan low uplift has an overpressure cap rock with a low loss rate, ranging from 0.5 to 0.66 m 3 / Ma*m 2 , with an average of 0.58m 3 / Ma*m 2 It can be seen that the abnormally high-pressure cap rock in Lingnan Low Uplift can better seal the buried-hill gas reservoir, and the loss rate is only 6.8% of the normal-pressure cap rock in Songnan Low Uplift, with a good sealing effect.

[0084] Table 4 Statistics of gas reservoir loss rates in typical structures of Songnan Low Uplift and Lingnan Low Uplift

[0085]

[0086] ② The correlation between the drilling loss rate and the well logging gas layer thickness of the typical structures of Songnan Low Uplift and Lingnan Low Uplift in the Qiongdongnan Basin was analyzed. Figure 4 As shown in Figure 2, it can be seen that for buried hill natural gas reservoirs, the gas layer thickness and the loss rate are negatively correlated, and the correlation is good. 2 =0.8286, that is, the better the preservation conditions (the smaller the loss rate), the thicker the gas layer. According to the fitting formula (Equation 7) of the loss rate and the thickness of the gas layer in all reservoir wells in the study area, the thickness of the gas layer H is taken as 气 The dissipation rate when it is 0 is 10.445m 3 / Ma*m 2 Therefore, the upper limit of the gas loss rate of the buried hill gas reservoirs in Songnan Low Uplift and Lingnan Low Uplift in the Qiongdongnan Basin is finally determined to be 10m 3 / Ma*m 2 In the subsequent evaluation of the plane distribution characteristics of the preservation conditions of the buried-hill gas reservoir, it is believed that the loss rate is greater than 10m 3 / Ma*m 2 It is a non-favorable area.

[0087] V 失 =0.0001H 气 2 -0.084H 气 +10.445

[0088] Where: v 失一气 Diffusion loss rate of natural gas in reservoir, m 3 / m 2 ·Ma;H 气－ Well logging gas layer thickness, m;

[0089] (5) Establish geological models of the overburden of the buried-hill gas reservoirs in the Songnan Low Uplift and Lingnan Low Uplift;

[0090] Based on the seismic reflection interfaces of the overburden of the Songnan low uplift and its surrounding buried hills in the Qiongdongnan Basin, including a total of 6 reflection interfaces, namely T70, T60, T50, T40, T30, and T00, as well as the mud content and cap rock thickness of wells Y8-1a, Y8-1b, Y8-3a, Y8-3b, Y10a, and Y13a, a cap rock geological model of the Songnan low uplift was established ( Figure 5a); A geological model of the caprock of the Lingnan low uplift was established based on the seismic reflection interfaces of the caprocks overlying the Lingnan low uplift and its surrounding buried hills, including a total of 6 reflection interfaces: T70, T60, T50, T40, T30, and T00, as well as the mud content and caprock thickness of wells LS26a and LS32a. Figure 5b ).

[0091] (6) Based on the data obtained in steps S1-S3 and the geological model established in step S5, a quantitative evaluation is performed on the planar distribution characteristics of the preservation conditions of the buried-hill gas reservoirs in the Songnan Low Uplift and the Lingnan Low Uplift in the Qiongdongnan Basin.

[0092] Geothermal gradient T in the Qiongdongnan Basin gd The seafloor temperature T0 is 4.31℃ / 100m, and the seafloor temperature T0 is 4℃. The temperature distribution characteristics of each layer of the overlying layer on Songnan Low Uplift and Lingnan Low Uplift are calculated according to Formula 5.

[0093] According to the pressure data and burial depth of the wells drilled in the Songnan Low Uplift and its surrounding buried hills, including Well Y8-1a, Well Y8-1b, Well Y8-3a, Well Y8-3b, Well Y10a, and Well Y13a, the paper Figure 6a ), the relationship between the pressure and depth of the Songnan low uplift is obtained, as shown in Equation 8-1; according to the pressure data of the buried hill wells in the Lingnan low uplift, including the L26a well and the L32a well, the pressure data and the burial depth are fitted ( Figure 6b ), and the relationship between the pressure of the Lingnan low uplift and the depth is obtained, as shown in Equation 8-2. Finally, based on the seismic reflection surface depth data of the overburden layer of the Songnan low uplift and the Lingnan low uplift, the pressure distribution characteristics of each layer are calculated.

[0094] p=(3E-12D 3 -4E-08D 2 +0.0002D+0.6735)×0.01D

[0095] p=(-7E-8D 2 +0.001D–1.1546)×0.01D

[0096] Where: p is pressure, MPa; D is burial depth, m.

[0097] Based on the logging porosity data of the cap layers of the buried hill wells in Songnan Low Uplift and Lingnan Low Uplift, including Well Y8-1a, Well Y8-1b, Well Y8-3a, Well Y8-3b, Well Y10a, Well Y13a, Well L26a and Well L32a, the distribution characteristics of the natural gas diffusion coefficient of each cap layer in the region were calculated using Formula 1.

[0098] According to the planar distribution characteristics of temperature, pressure and natural gas diffusion coefficient of each layer of the overburden layer on the buried hills of Songnan Low Uplift and Lingnan Low Uplift in the Qiongdongnan Basin, the natural gas concentration difference between each cap rock was calculated by "plane-to-plane" calculation. Finally, based on Fick's theorem, the planar distribution characteristics of the loss rate of the overburden layer on Songnan Low Uplift and Lingnan Low Uplift were obtained, and then the favorable preservation conditions or favorable targets can be selected on the plane.

[0099] Under the sealing of medium-thick mudstone at normal pressure, the natural gas loss rate of each structure in Songnan Low Uplift is quite different, which is mainly controlled by the thickness of the overburden layer on the buried hill. Among them, the loss rates of Y8-1a and Y8-1b wells in Y8-1 structure and Y8-3a and Y8-3b wells in Y8-3 structure are less than the upper limit of the loss rate of natural gas reservoirs in the study area (10m 3 / Ma*m 2 ), combined with the ultra-late continuous filling of natural gas, the Y8-1 and Y8-3 structures have large-scale natural gas accumulation in the buried hill reservoirs; while the Y13 structure is shallow and the overlying mudstone is a normal pressure cap rock, so the loss rate is greater than that of other structures, resulting in late natural gas loss and failure. Under the background of double sealing of overpressured and thick mudstone cap rocks, the natural gas loss rate of Lingnan Low Uplift is generally small, far less than the upper limit of the loss rate of natural gas reservoirs in the study area (10m 3 / Ma*m 2 ), the preservation conditions are good. Therefore, the loss rate of the overburden layer on the high-temperature and high-pressure buried hill in the Lingnan low uplift is low, and the preservation conditions in the whole area are good, which is a favorable preservation area. However, the loss rate of the shallow buried parts of the Songnan low uplift is large, which has exceeded the upper limit of the loss rate (10m 3 / Ma*m 2 ), that is, the Y10 structure and Y13 structure in the Songnan low uplift and their shallowly buried surrounding areas are unfavorable areas for preservation.

[0100] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for evaluating the preservation conditions of a high-temperature and high-pressure buried-hill gas reservoir, characterized in that: The steps include: S1. Obtain the diffusion coefficient of the overburden layer on the high-temperature and high-pressure buried-hill gas reservoir to be evaluated; S2. Determine the dissipation distance of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated; S3. Determine the concentration of each layer of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated; S4. Based on the data obtained in steps S1-S3, quantitatively evaluate the preservation conditions of the high-temperature and high-pressure buried hill structure to be evaluated according to Fick's law to obtain the dissipation rate value of the typical structure, analyze the correlation between the thickness of the gas layer of each structure and the dissipation rate, determine the upper limit of the dissipation rate value of the high-temperature and high-pressure buried hill to be evaluated, and determine the plane distribution characteristics of the preservation conditions of the buried hill gas reservoir in the area to be evaluated; S5. Establish a geological model of the overburden of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated; S6. Based on the data obtained in steps S1-S3 and the model established in step S5, quantitative evaluation is performed on the planar distribution characteristics of the preservation conditions of the high-temperature and high-pressure buried-hill gas reservoir to be evaluated according to Fick's law, and the difference in the sealing capacity of the overburden layer on the high-temperature and high-pressure buried-hill to be evaluated is determined, thereby determining the favorable preservation condition area or favorable target.

2. A method for evaluating storage conditions of high-temperature and high-pressure buried-hill gas reservoirs according to claim 1, characterized in that: In the step S1, the diffusion coefficient is obtained based on the porosity.

3. A method for evaluating storage conditions of a high-temperature and high-pressure buried-hill gas reservoir according to claim 1, characterized in that: In step S2, the dissipation distance is determined by the burial depth of each cap layer of the buried hill gas reservoir and the water depth.

4. A method for evaluating storage conditions of a high-temperature and high-pressure buried hill gas reservoir according to claim 1, characterized in that: In step S3, the concentration is determined according to the temperature and pressure characteristics of each cap layer of the buried hill gas reservoir.

5. A method for evaluating storage conditions of a high-temperature and high-pressure buried-hill gas reservoir according to claim 1, characterized in that: In step S5, the overlying stratum model of the buried-hill gas reservoir is established based on the reflection interfaces and lithological characteristics of each stratum overlying the high-temperature and high-pressure buried-hill gas reservoir to be evaluated.

6. A method for evaluating storage conditions of a high-temperature and high-pressure buried-hill gas reservoir according to claim 1, characterized in that: In step S6, the favorable preservation condition area or favorable target is determined by calculating the loss rate of the upper covering layer of the buried hill group of the high-temperature and high-pressure buried hill to be evaluated according to Fick's theorem.

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