A method for predicting favorable reservoirs in a fluvial facies compacted sandstone

Abstract

The present application relates to the technical field of oil and gas exploration and development, in particular to a fluvial facies tight sandstone favorable reservoir prediction method, comprising: based on geological and geophysical characteristics, establishing a fluvial facies tight sandstone reservoir static geological model; combining reservoir mineralogical characteristics and present formation water composition to restore reservoir diagenetic environment; based on the static geological model and the diagenetic environment, determining the boundary conditions of diagenetic numerical simulation, and carrying out reservoir diagenetic evolution numerical simulation; further constraining geophysical prediction results through numerical simulation results, and realizing the favorable reservoir prediction combining geology and geophysics. Through the prediction method, the problems of insufficient predictability of geological methods and low prediction accuracy of geophysical data can be effectively solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil and gas exploration and development, more particularly to the field of sedimentary reservoir, and particularly to a method for predicting favorable reservoirs in fluvial facies tight sandstone. BACKGROUND

[0002] Favorable reservoir prediction is an important research content in the field of oil and gas exploration and development, and is of great significance to guiding exploration area and layer selection and rational deployment of development well pattern. In particular, the tight sandstone reservoir has the characteristics of fine pore throat, various types, complex structure, poor correlation of porosity and permeability, nonlinear seepage, and strong heterogeneity. Therefore, it is of great significance to carry out favorable reservoir prediction for finding "sweet spot" area with relatively good physical property under the overall tight background, and to realize efficient exploration and rational development of tight sandstone oil and gas resources.

[0003] At present, favorable reservoir prediction is mainly based on the comprehensive analysis of geology and geophysics. The favorable reservoir prediction based on geological data mainly analyzes the control factors of favorable reservoir development through the comparison and analysis of the differences in geological conditions between favorable reservoirs and non-favorable reservoirs based on the known favorable reservoirs. Then, the favorable reservoirs are predicted. This method needs a large amount of drilling and geological sample analysis test data, and is limited to the extension of the known favorable reservoir development area. Therefore, the prediction is relatively limited. In addition, due to the limitation of drilling and geological data, this method is not suitable for low-mature exploration areas with few wells.

[0004] In summary, for the prediction of favorable reservoirs in tight sandstone, it is necessary to develop a new method for predicting favorable reservoirs by combining geophysical data with limited geological data, which can overcome the shortcomings of the geological method and the low prediction accuracy of the geophysical data. SUMMARY

[0005] To solve the above technical problems, the present application provides a method for predicting favorable reservoirs in fluvial facies tight sandstone, which can effectively solve the problems of insufficient prediction of the geological method and low prediction accuracy of the geophysical data.

[0006] The present application is achieved by adopting the following technical solutions:

[0007] A method for predicting favorable reservoirs in fluvial facies tight sandstone, comprising the following steps:

[0008] Step S1. Establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics; restoring reservoir diagenetic environment in combination with reservoir mineralogical characteristics and present formation water composition;

[0009] Step S2. Determining boundary conditions of diagenetic numerical simulation based on the static geological model and diagenetic environment, and carrying out reservoir diagenetic evolution numerical simulation;

[0010] Step S3. Further constraining geophysical prediction results by numerical simulation results to realize favorable reservoir prediction combining geology and geophysics.

[0011] The step S1 of establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics specifically refers to: establishing a static geological model of typical fluvial facies sand body deposition distribution through analysis of sand body deposition characteristics, sand body scale and morphology, determining the distribution range, internal period and structure of sand body, single sand body thickness distribution interval and overall sand ratio.

[0012] The method for determining the sand body deposition characteristics is: observing core material composition, lithology, particle size, color, biological disturbance, sedimentary structure and layer thickness of coring well, combining with logging and mud logging data, dividing the sedimentary lithofacies types of the study area based on sediment particle size, combining with sedimentary structure and material composition, and determining the lithofacies association type in combination with the different vertical stacking relationships of the lithofacies; determining the sedimentary microenvironment and sedimentary evolution process of the fluvial facies sand body through the relationship between the lithofacies association type and the sedimentary dynamic process.

[0013] The method for determining the sand body scale and morphology is: carrying out stratigraphic interpretation on three-dimensional seismic data, establishing a sequence stratigraphic framework, analyzing seismic attributes, and correcting seismic data using synthetic vertical seismic profile records; carrying out stratigraphic slice analysis, layer attribute extraction and interlayer attribute extraction by means of seismic sedimentology research method, and finely depicting the planar geometry and internal structure of fluvial facies sand body.

[0014] The step S1 of restoring reservoir diagenetic environment in combination with reservoir mineralogical characteristics and present formation water composition specifically refers to: determining the present diagenetic environment of the reservoir as the end point of diagenetic environment evolution through present formation water characteristic analysis and present reservoir diagenetic mineral type analysis, taking the original deposition material composition of the sand body as the starting point of diagenetic environment evolution, combining the formation sequence of minerals indicated by the replacement cutting relationship of diagenetic minerals and the representative diagenetic environment indication significance of different diagenetic minerals, and summarizing the reservoir diagenetic environment evolution process.

[0015] The present formation water characteristic analysis specifically refers to: obtaining the chemical composition of present formation water including formation water type, salinity size, pH value size, main ion type and different ion content in combination with oilfield production test results and geochemical test results.

[0016] The present reservoir diagenetic mineral type analysis specifically refers to: through sampling and grinding of a representative sample, casting thin section, reservoir material composition and diagenetic feature microscopic observation and analysis are carried out on the casting thin section to determine the main cementation type; on this basis, samples with early carbonate basement type strong cementation are selected to carry out mineral composition identification and XRD whole rock diffraction analysis, and the remaining part after removing the carbonate cementation is taken as the material composition of the original sedimentation of the sand body.

[0017] The step S2 specifically comprises the following steps:

[0018] Step S 21 . Determining the boundary conditions of diagenetic numerical simulation: based on the static geological model of the research area and the plane distribution characteristics of the sedimentary sand body, three-dimensional geodetic coordinates of the target work area are obtained; on the basis of determining the vertical sedimentary superposition characteristics of the key well area, a sand body distribution model consistent with the research work area range is established, and a three-dimensional grid model is constructed by combining the discrete network construction technology of the water-rock numerical simulation software; according to the obtained present formation water chemical composition, the initial parameters and chemical ions of water-rock interaction of diagenetic numerical simulation are determined;

[0019] Step S 22 . Diagenetic numerical simulation process control: diagenetic numerical simulation is carried out by using the water-rock interaction numerical simulation software, the coupling reaction process of two fluid phases of water, sodium chloride and carbon dioxide is considered in the simulation process, the chemical minerals and composition characteristics in the water-rock interaction simulation model are set, including the proportion, particle radius, surface area and unit of each mineral, and the water-rock reaction fluid inlet and fluid injection mode are further defined;

[0020] Step S 23 . Diagenetic numerical simulation result analysis: the related steps of simulation processing are set, including the start time, end time and maximum time step of water-rock numerical simulation, diagenetic simulation of different minerals is carried out, the corresponding results are output, and the difference distribution law of different minerals is further analyzed.

[0021] The initial parameters and chemical ions in the step S 21 include the density, porosity, permeability in three directions, thermal conductivity, specific heat and relative permeability calculation method of sandstone and mudstone sections.

[0022] The step S3 specifically refers to: according to the results of diagenetic numerical simulation, the internal heterogeneity of the favorable reservoir predicted by geophysical prediction is corrected, and then the distribution of the favorable reservoir in the low maturity exploration area is determined, so that the prediction of the favorable reservoir is realized.

[0023] Compared with the prior art, the beneficial effects of the present application are:

[0024] 1. The present application takes fluvial facies dense sandstone as the research object, combines limited geological data with geophysical data through diagenetic numerical simulation method, specifically, further constrains the geophysical prediction result through the numerical simulation result, realizes the favorable reservoir prediction combined with geology and geophysics, can solve the problems that the prediction based on geological data has limited extension range, the prediction based on geophysical data has relatively low precision, the relative thin layer favorable reservoir and the internal heterogeneity of the relative thick layer reservoir are limited in effect, and improves the accuracy and operability of the favorable reservoir prediction in the low mature exploration area.

[0025] 2. In the present application, based on the geological and geophysical characteristics, a static geological model of fluvial facies dense sandstone reservoir is established, the three-dimensional spatial distribution of the channel sand body can be finely described, and the geometric boundary condition of diagenetic simulation is more accurate.

[0026] 3. In the present application, the reservoir diagenetic environment is restored based on the reservoir mineralogical characteristics and the present formation water composition, so that the chemical boundary condition of diagenetic simulation is more accurate. BRIEF DESCRIPTION OF DRAWINGS

[0027] The present application will be further described in detail below in combination with the drawings and specific embodiments of the present application, in which:

[0028] Figure 1 It is a flowchart of the present application;

[0029] Figure 2 It is a schematic diagram of the sand body shape and scale of the root mean square amplitude attribute (RMS) of fluvial facies sand body in a certain area of Sichuan Basin in the present application;

[0030] Figure 3 It is a schematic diagram of the lithofacies combination type of fluvial facies sand body in a certain area of Sichuan Basin in the present application;

[0031] Figure 4 It is a schematic diagram of the static geological model of fluvial facies sand body in a certain area of Sichuan Basin in the present application;

[0032] Figure 5 It is a schematic diagram of the reservoir material composition and diagenetic characteristics of fluvial facies sand body in a certain area of Sichuan Basin in the present application;

[0033] Figure 6 It is a schematic diagram of the reservoir diagenetic evolution process of fluvial facies sand body in a certain area of Sichuan Basin in the present application;

[0034] Figure 7 It is a schematic diagram of the three-dimensional model construction of water-rock numerical simulation in the present application;

[0035] Figure 8 It is a schematic diagram of the three-dimensional spatial distribution of laumontite revealed by water-rock numerical simulation in the present application;

[0036] Figure 9 A schematic diagram of three-dimensional spatial distribution of calcite revealed by water-rock numerical simulation in the present application;

[0037] Figure 10 A schematic diagram of three-dimensional spatial distribution of kaolinite revealed by water-rock numerical simulation in the present application;

[0038] Figure 11 A schematic diagram of favorable reservoir distribution after correction based on diagenetic numerical simulation in the present application. DETAILED DESCRIPTION

[0039] Embodiment 1

[0040] As a basic embodiment of the present application, the present application comprises a method for predicting favorable reservoirs of fluvial facies tight sandstone, comprising the following steps: establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics; restoring the diagenetic environment of the reservoir in combination with the mineralogical characteristics of the reservoir and the composition of present-day formation water; determining the boundary conditions for diagenetic numerical simulation based on the static geological model and the diagenetic environment, and carrying out numerical simulation of diagenetic evolution of the reservoir; further constraining the geophysical prediction results by the numerical simulation results, and realizing the prediction of favorable reservoirs in combination with geology and geophysics.

[0041] Embodiment 2

[0042] As a preferred embodiment of the present application, the present application comprises a method for predicting favorable reservoirs of fluvial facies tight sandstone, comprising the following steps:

[0043] Step S1. Establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics; restoring the diagenetic environment of the reservoir in combination with the mineralogical characteristics of the reservoir and the composition of present-day formation water.

[0044] Specifically, the establishment of a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics refers to: establishing a static geological model of typical fluvial facies sand body deposition distribution through analysis of sand body deposition characteristics and sand body scale and morphology, and clarifying the distribution range, internal period and structure, single sand body thickness distribution interval and overall sand-to-ground ratio of the sand body.

[0045] Specifically, the restoration of the diagenetic environment of the reservoir in combination with the mineralogical characteristics of the reservoir and the composition of present-day formation water refers to: clarifying the present-day diagenetic environment of the reservoir as the end point of diagenetic environment evolution, taking the original deposition of the sand body as the starting point of diagenetic environment evolution, combining the formation sequence of minerals indicated by the replacement and cutting relationship of diagenetic minerals and the representative diagenetic environment indication significance of different diagenetic minerals, and summarizing the diagenetic environment evolution process of the reservoir.

[0046] Step S2. Based on the static geologic model and diagenetic environment, the boundary conditions of diagenetic numerical simulation are determined, and reservoir diagenetic evolution numerical simulation is carried out.

[0047] Step S3. The geophysical prediction result is further constrained by the numerical simulation result, and the favorable reservoir prediction combining geology and geophysics is realized. Specifically, according to the result of diagenetic numerical simulation, the internal heterogeneity of the favorable reservoir predicted by geophysics is corrected, and then the distribution of the favorable reservoir in the low-maturity exploration area is determined, so as to realize the purpose of favorable reservoir prediction.

[0048] Embodiment 3

[0049] As another preferred embodiment of the present application, the present application comprises a method for predicting favorable reservoirs of fluvial facies tight sandstone, comprising the following steps:

[0050] Step S1. Based on the geological and geophysical characteristics, a static geologic model of the fluvial facies tight sandstone reservoir is established; and the reservoir diagenetic environment is restored in combination with the reservoir mineralogical characteristics and the present formation water composition.

[0051] Specifically, the static geologic model of the fluvial facies tight sandstone reservoir is established based on the geological and geophysical characteristics, and comprises the following steps:

[0052] (1) The scale and shape of the sand body are determined. The stratum interpretation is carried out on the three-dimensional seismic data by using the PaleoScan software, the sequence stratigraphic framework is established, the seismic attributes are analyzed, and the seismic data are corrected by using the synthetic vertical seismic profile record. By means of the seismic sedimentology research method, various analyses such as stratum slicing analysis, layer attribute extraction, and interlayer attribute extraction are carried out, and the planar geometry and internal structure of the fluvial facies sand body are finely described.

[0053] (2) The typical sedimentary characteristics of the sand body are determined. The sedimentary facies types in the research area are divided based on the sediment particle size, combined with the sedimentary structure and material composition, and the lithofacies association types are determined in combination with the different vertical stacking relationships of the lithofacies. The sedimentary microenvironment and sedimentary evolution process of the fluvial facies sand body are determined through the relationship between the lithofacies association types and the sedimentary dynamic process.

[0054] (3) The static geologic model is established. Through the analysis of the sedimentary characteristics, scale and shape, the static geologic model of the sedimentary distribution of the typical fluvial facies sand body is established, and the distribution range, internal period and structure, single sand body thickness distribution interval, and overall sand ratio of the sand body are determined.

[0055] Specifically, the reservoir diagenetic environment is restored in combination with the reservoir mineralogical characteristics and the present formation water composition, and comprises the following steps:

[0056] (1) Reservoir petrology and geochemical characteristics analysis. Through sampling and grinding of representative samples, the cast thin section was observed and analyzed by Cessier Axioscope A1 APOL. digital transmission reverse polarization microscope to determine the main cement types. On this basis, mineral composition identification and XRD whole rock diffraction analysis were carried out on samples with early carbonate-based strong cementation, and the remaining part after removing carbonate cement was used as the original sedimentary material composition of the sand body.

[0057] (2) Analysis of the ion composition characteristics of the present formation water of the reservoir. According to the combination of geochemical test results and oilfield production test results, the chemical composition of the present formation water was obtained, including the type of formation water, the size of salinity, the size of pH value, the type of main ions and the content of different ions, etc.

[0058] (3) Reservoir diagenetic environment evolution recovery. Through the analysis of the characteristics of the present formation water and the analysis of the present reservoir diagenetic mineral types, the present diagenetic environment of the reservoir was determined as the endpoint of the diagenetic environment evolution, and the original sedimentary material composition of the sand body was used as the starting point of the diagenetic environment evolution. Combined with the formation sequence of minerals indicated by the replacement cutting relationship of diagenetic minerals and the representative diagenetic environment indication significance of different diagenetic minerals, the reservoir diagenetic environment evolution process was summarized.

[0059] Step S2. Based on the static geological model and the diagenetic environment, the boundary conditions of the diagenetic numerical simulation were determined, and the reservoir diagenetic evolution numerical simulation was carried out. Specifically including the following steps:

[0060] Step S 21 . Determine the boundary conditions of the diagenetic numerical simulation. Based on the static geological model of the study area, guided by the planar distribution characteristics of the sedimentary sand body, combined with the three-dimensional digital extraction software Getdata to obtain the three-dimensional geodetic coordinates of the target work area. On the basis of clarifying the vertical sedimentary superposition characteristics of the key well area, a sand body distribution model consistent with the research work area was established, and a three-dimensional grid model was constructed by combining the discrete network construction technology of the water-rock numerical simulation software. According to the obtained present formation water chemical composition, the initial parameters and chemical ions of water-rock interaction in diagenetic numerical simulation were determined, including the density, porosity, permeability in three directions, thermal conductivity, specific heat and relative permeability calculation method of sandstone and mudstone section.

[0061] Step S 22. Petrologic numerical simulation process control. The numerical simulation software of water-rock interaction (Tough-2 and Tough-react modules in PetraSim) is used to carry out petrologic numerical simulation. The coupling reaction process of two fluid phases of water, sodium chloride and carbon dioxide is considered in the simulation process. The chemical minerals and composition characteristics in the water-rock interaction simulation model are set, including the proportion, particle radius (m), surface area (m 2 ) and unit of each mineral, and the water-rock reaction fluid inlet and fluid injection mode are further defined.

[0062] Step S 23 . Petrologic numerical simulation result analysis. The simulation processing related steps such as the start time, end time and maximum time step of water-rock numerical simulation are set, and then the petrologic simulation of different minerals is carried out, the corresponding results are output, and the difference distribution law of different minerals is further analyzed, specifically the distribution law of main cement.

[0063] Step S3. The results of numerical simulation are further constrained to predict the results of geophysics, and the favorable reservoir prediction of geology and geophysics is realized. Specifically, according to the results of petrologic numerical simulation, that is, the distribution law of main cement, combined with the sand body genesis and sand body distribution obtained by studying the static geological model, the internal heterogeneity of the favorable reservoir predicted by geophysics is corrected, and then the distribution of the favorable reservoir in the low mature exploration area is determined, and the purpose of favorable reservoir prediction is realized.

[0064] Example 4

[0065] As another embodiment of the present application, referring to the description attached Figure 1 , the present application comprises a method for predicting favorable reservoirs of fluvial facies tight sandstone, taking the prediction of favorable reservoirs of fluvial facies tight sandstone in a certain area of Sichuan Basin as an example, which specifically comprises the following steps:

[0066] Step S1. Based on the geological and geophysical characteristics, a static geological model of fluvial facies tight sandstone reservoir is established. The reservoir diagenetic environment is restored by combining the reservoir mineralogical characteristics and present formation water composition.

[0067] Among them, based on the geological and geophysical characteristics, a static geological model of fluvial facies tight sandstone reservoir is established, which specifically comprises the following steps:

[0068] (1) Taking the fluvial facies tight sandstone in a certain area of Sichuan Basin as the research object, through the analysis of three-dimensional seismic data, the stratum interpretation of three-dimensional seismic data is carried out by using PaleoScan software, the sequence stratigraphic framework is established, and the geometric shape and plane distribution characteristics of sand body are analyzed by using root mean square amplitude attribute (RMS). Referring to the description attached Figure 2The sand body shape of the root mean square amplitude attribute display is a typical meandering sand body formed by the point bar side accumulation of the river channel; the internal attribute strength has obvious differences, further indicating that the sand body migration inside the river channel results in the convex bank being mainly sandy deposition and the concave bank being mainly muddy deposition; meanwhile, the internal strong heterogeneity of the sandy deposition of the convex bank indicates the superimposed comprehensive geophysical response of different period sand bodies.

[0069] (2) Core observation analysis was carried out on typical coring wells, and through the different vertical superimposed relationship of lithofacies, referring to the lithofacies classification in the description Figure 3 , four kinds of lithofacies combination types were established. They are composite channel-filling sedimentary lithofacies combination (FA1), isolated channel-filling sedimentary lithofacies combination (FA2), splay sedimentary lithofacies combination (FA3), and overflow sedimentary lithofacies combination (FA4). Referring to the lithofacies combination in the description Figure 3 , Fig. (a), the composite channel-filling sedimentary lithofacies combination is mainly composed of massive conglomerate facies, trough cross-bedded sandstone facies and parallel-bedded sandstone facies. Referring to the lithofacies combination in the description Figure 3 , Fig. (b), the isolated channel-filling sedimentary lithofacies combination is mainly composed of trough cross-bedded sandstone facies and plate cross-bedded sandstone facies. Referring to the lithofacies combination in the description Figure 3 , Fig. (c), the splay sedimentary lithofacies combination is mainly composed of trough cross-bedded sandstone facies, parallel-bedded sandstone facies, normal grading sandstone facies, miscellaneous accumulation facies and sand ripple cross-bedded siltstone facies. Referring to the lithofacies combination in the description Figure 3 , Fig. (d), the overflow sedimentary lithofacies combination is mainly composed of sand ripple cross-bedded siltstone facies, horizontal-bedded siltstone facies, miscellaneous accumulation facies and purple mudstone facies. It is further confirmed that the study area is a typical fluvial facies deposition sand body.

[0070] (3) Through fine analysis of the geophysical distribution characteristics and sedimentary characteristics, referring to the lithofacies combination in the description Figure 4 , a static geological model of fluvial facies sand body deposition in a certain area of Sichuan Basin is established. The overall channel deposition is developed, the sandy channel deposition is surrounded by splay and overflow deposition, the internal multi-period superimposed sandy channel deposition forms a vertically normal grading superimposed channel sand body deposition, the near-end sandy channel deposition is developed, and the sand ratio is relatively high. With the increase of the transport distance, the content of sandy deposition gradually decreases, the content of muddy deposition gradually increases, and the sand ratio gradually decreases.

[0071] Among them, the reservoir diagenetic environment is restored by combining the reservoir mineralogical characteristics and the present formation water composition, which specifically includes the following steps:

[0072] (1) The present reservoir diagenetic mineral type analysis specifically refers to: through sampling and grinding of representative samples, casting thin sections, using Zeiss Axioscope A1 APOL. digital transmission reverse polarizing microscope to observe and analyze the reservoir material composition and diagenetic characteristics of the casting thin sections, the reservoir diagenetic types in the study area are diverse, including constructive chemical diagenesis and destructive chemical diagenesis. The constructive diagenesis is mainly feldspar and detritus dissolution. The destructive diagenesis is mainly precipitation of different types of cements, including laumontite cementation, calcite cementation, siliceous cementation, albite cementation, clay mineral cementation, etc., and the material composition and diagenetic characteristics are shown in the drawings of the specification Figure 5 . Specifically, Figure (a) in the specification Figure 5 is a sample under feldspar dissolution collected at a depth of 2224.1 m in Well A, and the characteristic diagram under single polarized light; Figure (b) in the specification Figure 5 is a sample under laumontite dissolution collected at a depth of 2654.5 m in Well B, and the characteristic diagram under single polarized light; Figure (c) in the specification Figure 5 is a sample under zeolite cementation collected at a depth of 2654.5 m in Well B, and the characteristic diagram under single polarized light; Figure (d) in the specification Figure 5 is a sample under zeolite cementation collected at a depth of 2654.5 m in Well B, and the characteristic diagram under crossed light; Figure (e) in the specification Figure 5 is a sample under calcite cementation collected at a depth of 1808.5 m in Well C, and the characteristic diagram under single polarized light; Figure (f) in the specification Figure 5 is a sample under quartz secondary enlargement collected at a depth of 2153.5 m in Well D, and the characteristic diagram under single polarized light; Figure (g) in the specification Figure 5 is a sample under feldspar secondary enlargement collected at a depth of 2153.48 m in Well E; Figure (h) in the specification Figure 6 is a sample under albite collected at a depth of 2009.9 mm in Well F, and the characteristic diagram under single polarized light.

[0073] (2) The present formation water characteristic analysis specifically refers to: the present pressure and temperature analysis of the study area indicates that the whole is in a normal pressure state, the temperature is about 70-75 degrees, and the formation temperature is relatively low. As shown in Table 1 below, the formation water characteristics show low salinity characteristics, which are much smaller than the present seawater salinity. The present formation water pH is mostly less than 7, and the whole is an acidic diagenetic environment; the formation water is mainly CaCl2 type, indicating that the formation as a whole is well sealed.

[0074] Table 1 Present formation water characteristics of fluvial facies reservoirs in a certain area of Sichuan Basin

[0075]

[0076] (3) Reservoir diagenetic environment evolution recovery. The reservoir is currently in an acidic diagenetic environment. According to the dissolution and filling characteristics and the self-diagenetic mineral replacement cutting relationship and the relationship between hydrocarbon charging and cementation, the diagenetic evolution process of the reservoir in the research area is analyzed to be: compaction → calcite cementation / gypsum cementation / early laumontite cementation / clay coating (montmorillonite and chlorite) → feldspar dissolution / higherite precipitation / quartz increase → illite-smectite mixed layer coating → late laumontite precipitation / iron-containing calcite precipitation / albite precipitation / chlorite coating growth → laumontite dissolution / carbonate dissolution / anhydrite dissolution, as shown in the accompanying drawings of the specification. Figure 7

[0077] Step S2. Based on the static geological model and the diagenetic environment, the boundary conditions of the diagenetic numerical simulation are determined, and the reservoir diagenetic evolution numerical simulation is carried out. Specifically, the following steps are included:

[0078] Step S 21 Based on the static geological model of the fluvial facies sedimentary sand body, a stratigraphic framework model consistent with the research area range is established, which is mudstone-sandstone-mudstone from top to bottom, and the rock layer thickness is consistent with the actual well area analysis data as much as possible. In this simulation, the stratigraphic thickness is set to 20 m, 50 m and 30 m respectively. Combined with the water-rock numerical simulation software discrete network construction technology, the grid scale factors in x-axis direction and y-axis direction are set to 1.0495, and the grid in z-axis direction is set as the standard of stratification. The three-dimensional grid model of the target layer of the research area is constructed, as shown in the accompanying drawings of the specification. Figure 8 Combined with the current formation water chemical composition obtained from the oilfield production test results and the geochemical test results, such as Table 1 shown above, the initial parameters and chemical ions of water-rock interaction are determined, including the density, porosity, permeability in three directions, thermal conductivity, specific heat and relative permeability calculation method of sandstone and mudstone layers. Among them, the chemical parameters corresponding to the sandstone and mudstone are shown in Table 2. In the simulation process, the coupling reaction process of two fluid phases of water, sodium chloride and carbon dioxide is considered, the initial temperature is set to 75℃, the initial pressure is set to 2.0e7 Pa, the salt mass fraction is set to 0.06, and the ECO2N state reaction mode is selected. According to the test results in the research area, the initial chemical reaction ions are set to AlO 2- , Ca 2+ , Cl - , Fe 2+ , H + , H2O, HCO3 - , K + , Mg 2+ , Na + , O2(aq), SiO2(aq), SO4 2- .​

[0079] Table 2 Chemical parameters of sandstone and mudstone in water-rock numerical simulation

[0080]

[0081] Step S 22 . On the basis of determining the initial ions of water-rock simulation experiment and the minerals involved in the reaction in the solution, the chemical minerals and composition characteristics in the water-rock interaction simulation model are set, including the proportion, particle radius (m), surface area (m 2 ) and unit of each mineral. The minerals include albite, ankerite, calcite, diaspore, dolomite, hematite, illite, potassium feldspar, kaolinite, magnesite, more feldspar, pyrite, quartz, siderite, calcium montmorillonite, sodium montmorillonite, chlorite and laumontite, and the specific parameter settings are shown in Table 3. Among them, the radius of the mineral particles is set to 0.001 m, and the unit is cm 2 / g of mineral. The proportions of albite and other minerals are set to 0.015, 0.015, 0.01929, 0.004, 0.0002, 0.00497, 0.00954, 0.08179, 0.02015, 0.003, 0.19795, 0.001, 0.57888, 0.0056, 0.0028, 0.03897, 0.004556, 0.0065, respectively. Similarly, the surface area sizes of albite, ankerite and other minerals are set to 9.8, 9.8, 9.8, 9.8, 9.8, 9.8, 12.87, 151.63, 9.8, 151.6, 9.8, 9.8, 12.87, 9.8, 9.8, 151.63, 151.63, 9.8, 9.8, respectively. The setting of all parameters refers to the numerical values of chemical parameters of different minerals in the water-rock numerical simulation software PetraSim. On the basis of setting the chemical components and mineral parameters, the fluid inlet and fluid injection mode of the study area are defined. In the process of this study, three substances such as injection water, NaCl and CO2 are injected, and the flow rate and enthalpy are 30 kg / s and 920.0 J / kg, 15 kg / s and 920.0 J / kg, and 10 kg / s and 920.0 J / kg, respectively.

[0082] Table 3 Chemical minerals and composition characteristics in the water-rock interaction simulation model

[0083]

[0084] Step S 23Based on the water-rock numerical simulation software platform PetraSim, combined with the above experimental principle and experimental steps, the starting time, ending time, maximum time step and other simulation processing related steps of the water-rock numerical simulation are set, and then the diagenetic simulation of different minerals is carried out, and the three-dimensional spatial distribution characteristics of the main cement of the target layer in the research area, i.e. laumontite, calcite and kaolinite, are studied. Specifically, the three-dimensional spatial distribution characteristics of the laumontite are as shown in the accompanying drawings of the specification Figure 9 , the three-dimensional spatial distribution characteristics of the calcite are as shown in the accompanying drawings of the specification Figure 10 , and the three-dimensional spatial distribution characteristics of the kaolinite are as shown in the accompanying drawings of the specification Figure 11 .

[0085] In order to more intuitively display the distribution characteristics of minerals in different regions and different directions, three north-south lines and three east-west lines are selected for the target layer in the research area, and the basis for selecting the lines is mainly to refer to the sand body distribution characteristics in the research area to display the mineral distribution law in the key well area. In the simulation results, the blue area represents a region with relatively low mineral content, and the red area represents a region with relatively high mineral content. The correlation between the laumontite precipitation area and the mudstone interface is not obvious, the laumontite is developed in the relatively good thick sand body, and is mainly controlled by the material composition and fluid migration. The distribution of calcite is obviously controlled by the adjacent mudstone, and the calcite presents a high value near the mudstone, the calcite content in the middle of the thick sand body is low, and is mainly controlled by the sand body thickness and exogenous carbonate. The distribution of kaolinite presents a relatively high value at the upper interface, and atmospheric fresh water leaching may be the main source of exogenous kaolinite, and feldspar dissolution provides part of the endogenous kaolinite source.

[0086] Step S3. Further constrain the geophysical prediction results by the numerical simulation results to realize the favorable reservoir prediction combining geology and geophysics.

[0087] Specifically, according to the results of the diagenetic numerical simulation, the internal heterogeneity of the favorable reservoir predicted by the geophysics is corrected, the laumontite, calcite and kaolinite strong cementation areas are superimposed on the plane, and the laumontite, calcite and kaolinite strong cementation areas are deducted from the original geophysical prediction of the favorable reservoir distribution area, i.e. the more accurate favorable reservoir distribution area, as shown in the accompanying drawings of the specification ​ , thereby realizing the purpose of accurate prediction of the favorable reservoir in the low mature exploration area.

[0088] In summary, after reading the present application document, according to the technical scheme and technical concept of the present application, various corresponding transformation schemes made by ordinary skilled personnel in the art without creative mental effort are all within the scope of protection of the present application.

Claims

1. A method of predicting favorable reservoirs in fluvial, tight sandstones, characterized in that: The method comprises the following steps: Step S1. Establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics; combining reservoir mineralogical characteristics and present formation water composition to restore the reservoir diagenetic environment; Step S2. Determining boundary conditions of diagenetic numerical simulation based on the static geological model and the diagenetic environment, and carrying out reservoir diagenetic evolution numerical simulation; specifically comprising the following steps: Step S 21 . Determine the boundary conditions of diagenetic numerical simulation: based on the static geological model of the study area and guided by the planar distribution characteristics of the sedimentary sand body, obtain the three-dimensional geodetic coordinates of the target work area; on the basis of clarifying the vertical sedimentary stacking characteristics of the key well area, establish a sand body distribution model consistent with the scope of the study area, and construct a three-dimensional grid model in combination with the discrete network construction technology of the water-rock numerical simulation software; according to the obtained present-day formation water chemical composition, determine the initial parameters and chemical ions of the water-rock interaction of diagenetic numerical simulation; Step S 22 . Diagenetic numerical simulation process control: numerical simulation software of water-rock interaction is used to carry out diagenetic numerical simulation. The coupling reaction process of two fluid phases of water, sodium chloride and carbon dioxide is considered in the simulation process. The chemical minerals and composition characteristics in the water-rock interaction simulation model are set, including the proportion, particle radius, surface area and unit of each mineral, and the water-rock reaction fluid inlet and fluid injection mode are further defined; Step S 23 . Analysis of the results of the diagenetic numerical simulation: The relevant steps of the simulation process are set, including the start time, end time and maximum time step of the water-rock numerical simulation, the diagenetic simulation of different minerals is carried out, the corresponding results are output, the difference distribution law of different minerals is further analyzed, and the distribution law of the main cement is obtained; Step S3. Further constraining geophysical prediction results by numerical simulation results, and realizing favorable reservoir prediction combining geology and geophysics; specifically referring to: according to the results of diagenetic numerical simulation, i.e. the distribution of main cements, correcting the internal heterogeneity of the favorable reservoir predicted by geophysics, and then determining the distribution of the favorable reservoir in the low-maturity exploration area, and realizing the prediction of the favorable reservoir.

2. A method of predicting a favorable reservoir in a fluvial, tight sandstone according to claim 1, characterized in that: The step S1 of establishing a static geological model of fluvial facies tight sandstone reservoir based on geological and geophysical characteristics specifically refers to: through the analysis of sand body sedimentary characteristics, sand body scale and morphology, a static geological model of typical fluvial facies sand body sedimentary distribution is established, and the distribution range, internal period and structure, single sand body thickness distribution interval and overall sand ratio of the sand body are determined.

3. A method of predicting a favorable reservoir in a fluvial dense sandstone according to claim 2, characterized in that: The method for determining the sand body sedimentary characteristics is: through the observation of core material composition, lithology, particle size, color, biological disturbance, sedimentary structure and layer thickness of the coring well, combined with logging and mud logging data, based on sediment particle size, combined with sedimentary structure and material composition, the sedimentary facies types in the study area are divided, and then combined with the different vertical stacking relationships of the lithofacies, the lithofacies combination types are determined; through the relationship between the lithofacies combination types and the sedimentary dynamic process, the sedimentary microenvironment and the sedimentary evolution process of the fluvial facies sand body are determined.

4. A method of predicting a favorable reservoir in a fluvial dense sandstone according to claim 2, characterized in that: The method for determining the sand body scale and morphology is: stratum interpretation is carried out on the three-dimensional seismic data, a sequence stratigraphic framework is established, seismic attributes are analyzed, and the seismic data is corrected by using synthetic vertical seismic profile records; with the help of seismic sedimentology research method, stratum slice analysis, layer attribute extraction and interlayer attribute extraction are carried out, and the planar geometric morphology and internal structure of the fluvial facies sand body are finely described.

5. A method of predicting a favorable reservoir in a fluvial dense sandstone according to claim 4, characterized in that: PaleoScan software is used to carry out stratum interpretation on the three-dimensional seismic data.

6. A method of predicting a favorable reservoir in a fluvial dense sandstone according to claim 1 or 2, characterized in that: The step S1 of combining reservoir mineralogical characteristics and present formation water composition to restore the reservoir diagenetic environment specifically refers to: through the analysis of present formation water characteristics and present reservoir diagenetic mineral types, the present diagenetic environment of the reservoir is determined as the end point of the diagenetic environment evolution, the original sedimentary material composition of the sand body is taken as the starting point of the diagenetic environment evolution, the formation order of the minerals indicated by the diagenetic mineral replacement cutting relationship and the representative diagenetic environment indicated by different diagenetic minerals are combined, and the reservoir diagenetic environment evolution process is summarized.

7. A method of predicting a favorable reservoir in a fluvial, consolidated sandstone according to claim 6, characterized in that: The present formation water characteristic analysis specifically refers to: combining oilfield production test results and geochemical test results, the chemical composition of the present formation water is obtained, including formation water type, salinity size, pH value size, main ion type and different ion content.

8. A method of predicting a favorable reservoir in a fluvial dense sandstone according to claim 6, characterized in that: The present reservoir diagenetic mineral type analysis specifically refers to: through sampling and grinding of representative samples, casting thin sections are subjected to reservoir material composition and diagenetic feature microscopic observation analysis to determine main cement types; on this basis, samples with early carbonate basement type strong cementation are selected to carry out mineral composition identification and XRD whole rock diffraction analysis, and the remaining part after removing the carbonate cement is taken as the original sedimentary material composition of the sand body.

9. A method of predicting favorable reservoirs in fluvial, consolidated sandstones according to claim 1, characterized in that: The step S 21 The initial parameters and chemical ions include the density, porosity, three-directional permeability, thermal conductivity, specific heat, and relative permeability calculation method of sandstone and mudstone sections.

10. A method of predicting favorable reservoirs in fluvial, consolidated sandstones according to claim 1, characterized in that: Step S 22 The numerical simulation adopts Tough-2 and Tough-react modules in PetraSim platform.

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