Method and system for predicting vertical connectivity of middle fault of petroliferous basin

Abstract

The invention discloses a method and a system for predicting the vertical connectivity of a fault in a petroliferous basin, and relates to the technical field of fault connectivity detection.The method comprises the steps of determining a fault vertical connectivity coefficient of a target position according to influence factors of the fault vertical connectivity of the target position; the influence factors comprise the thickness of the fractured cover layer, the shale content, the normal stress of the fault surface, the formation fluid pressure, the brittleness degree of the cover layer and the fault displacement of the fault; the target position is the target position of a non-drilling area in the petroliferous basin; and predicting the vertical connectivity of the target position according to the fault vertical connectivity coefficient of the target position. According to the method, the identification accuracy of the vertical connectivity of the fault in the petroliferous basin is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of fault connectivity detection, and particularly to a method and system for predicting the vertical connectivity of faults in an oil and gas bearing basin. Background Art

[0002] The dual role of faults in the migration and accumulation of oil and gas has always been a hot topic in the research of oil and gas bearing basins. A large number of studies have shown that faults can either be channels for fluid migration or barriers to fluid migration. Moreover, the evolution of faults is periodic, with characteristics of intermittent activity, opening, and closing and blocking. During the active period, faults mostly appear in an open state and can serve as channels for oil and gas migration, while during the static period, they often appear in a closed state and play a role in blocking oil and gas. When acting as a channel, faults can not only connect the source rock and the reservoir to form a preferential channel for oil and gas migration, but also destroy the early formed oil and gas reservoirs and play an adjustment role on the oil and gas therein, causing the oil and gas to migrate along the fault to shallower horizons for hydrocarbon accumulation or dissipation. When acting as a barrier, faults can block the migration or dissipation of oil and gas along the fault to shallower horizons.

[0003] A large amount of field outcrop, core, microscopic analysis and other data show that faults are complex three-dimensional geological bodies, generally having a "dual" structure, namely the fault core and the fracture zone. With the influence of the periodic activity of faults, the change of overlying rock pressure, and diagenetic cementation and other effects during the fluid flow process, the permeability of the fracture zone is in a dynamic evolution process. In different evolution stages of the fault, there are significant differences in the permeability changes of the fault core and the fracture zone, playing different roles as migration channels or blocking barriers at different stages. However, the fluid conduction ability of faults in the geological history is affected by many geological factors, and the roles played by faults in fluid migration and accumulation in different evolution stages are very complex.

[0004] Currently, the methods for predicting the connectivity of faults in oil and gas bearing basins are mostly qualitative - semi - quantitative methods. Although predecessors have proposed methods for predicting fault connectivity with multiple factors, they have not considered the influence of rock brittleness on fault connectivity during the vertical migration of oil and gas along faults. Therefore, the accuracy of identifying the vertical connectivity of faults in oil and gas bearing basins remains to be improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a method and system for predicting the vertical connectivity of faults in an oil and gas bearing basin, improving the accuracy of identifying the vertical connectivity of faults in an oil and gas bearing basin.

[0006] To achieve the above purpose, the present invention provides the following solutions:

[0007] A method for predicting the vertical connectivity of faults in an oil and gas bearing basin, comprising:

[0008] Determine the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location; the influencing factors include the thickness of the faulted caprock, shale content, normal stress on the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw; the target location is the target location in the un-drilled area of the oil and gas basin.

[0009] Predict the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location.

[0010] Optionally, determining the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location specifically includes:

[0011] Determine the shale smear factor according to the thickness of the faulted caprock, the shale content, and the fault throw;

[0012] Substitute the shale smear factor, the formation fluid pressure, and the normal stress on the fault plane into the calculation formula of the vertical connectivity coefficient of the fault, and calculate the vertical connectivity coefficient of the fault at the target location;

[0013] The calculation formula of the vertical connectivity coefficient of the fault is expressed as:

[0014]

[0015] Among them, FPI represents the vertical connectivity coefficient of the fault, P represents the formation fluid pressure, σ N represents the normal stress on the fault plane, SGR represents the shale smear factor, and BI is the brittleness index.

[0016] Optionally, the shale smear factor is expressed as:

[0017]

[0018] Among them, V sh represents the shale content, D represents the fault throw, ΔZ i represents the thickness of the i-th layer of rock, and n represents the number of layers of the faulted caprock.

[0019] Optionally, the brittleness index is expressed as:

[0020]

[0021] Among them, E brit is the normalized Young's modulus, and v brit is the normalized Poisson's ratio.

[0022] Optionally, predicting the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location specifically includes:

[0023] If the vertical connectivity coefficient of the fault at the target location is greater than the maximum value of the critical region, the target location is predicted to be connected;

[0024] If the vertical connectivity coefficient of the fault at the target location is less than the minimum value of the critical region, the target location is predicted to be unconnected;

[0025] If the vertical connectivity coefficient of the fault at the target location is within the critical region, the target location is predicted to be in an intermediate state.

[0026] Optionally, the normal stress of the fault plane is expressed as:

[0027] σ N =(sinθ1·(sinθ2) 2 σ H +(cosθ1·sinθ2) 2 σ h +cosθ2 2 S v ;

[0028] Wherein, σ N represents the normal stress of the fault plane, θ1 is the angle between the fault strike and the maximum horizontal principal stress, θ2 is the fault dip angle, σ H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; S v is the vertical principal stress.

[0029] Optionally, the formation fluid pressure is expressed as:

[0030]

[0031] Wherein, P is the formation fluid pressure, S v is the vertical principal stress, P h is the hydrostatic pressure at the depth corresponding to the target location, Δt norm is the acoustic travel time at the depth corresponding to the target location in the gradient of the normal acoustic travel time with depth, and Δt is the actual acoustic travel time at the depth corresponding to the target location.

[0032] The present invention discloses a system for predicting the vertical connectivity of faults in an oil and gas bearing basin, including:

[0033] A vertical connectivity coefficient determination module of the fault, configured to determine the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location; the influencing factors include the thickness of the faulted caprock, the shale content, the normal stress of the fault plane, the formation fluid pressure, the brittleness degree of the caprock, and the fault throw; the target location is the target location in the undrilled area of the oil and gas bearing basin;

[0034] A vertical connectivity prediction module for predicting the vertical connectivity of a target location according to the vertical connectivity coefficient of a fault at the target location.

[0035] According to the specific embodiments provided by the present invention, the following technical effects are disclosed:

[0036] Among the influencing factors for calculating the vertical connectivity coefficient of a fault at a target location in the present invention, not only the thickness of the faulted caprock, shale content, normal stress on the fault plane, formation fluid pressure, and fault throw are included, but also the brittleness degree of the caprock is included, which improves the accuracy of the vertical connectivity coefficient of the fault, thereby improving the accuracy of identifying the vertical connectivity of the fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0038] Figure 1 Schematic flow diagram of a method for predicting the vertical connectivity of faults in an oil and gas basin provided by an embodiment of the present invention;

[0039] Figure 2 Schematic diagram for discriminating the vertical connectivity of faults provided by an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the normal stress distribution on the fault plane provided by an embodiment of the present invention;

[0041] Figure 4 Schematic diagram of the fluid pressure in the study area provided by an embodiment of the present invention;

[0042] Figure 5 Schematic diagram of the SGR calculation model provided by an embodiment of the present invention;

[0043] Figure 6 Schematic diagram of the brittle index calculated by well logging in the study area provided by an embodiment of the present invention;

[0044] Figure 7 Schematic diagram for predicting the vertical connectivity of the fault plane provided by an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0046] The object of the present invention is to provide a method and system for predicting the vertical connectivity of faults in an oil and gas bearing basin, which improves the accuracy of identifying the vertical connectivity of faults in an oil and gas bearing basin.

[0047] In order to make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Embodiment 1

[0049] As Figure 1 shown, a method for predicting the vertical connectivity of faults in an oil and gas bearing basin provided in this embodiment includes the following steps.

[0050] Step 101: Determine the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location; the influencing factors include the thickness of the faulted caprock, shale content, normal stress on the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw; the target location is the target location in the un-drilled area of the oil and gas bearing basin.

[0051] Step 102: Predict the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location.

[0052] Among them, step 101 specifically includes:

[0053] Determine the shale smear factor according to the thickness of the faulted caprock, the shale content, and the fault throw.

[0054] Substitute the shale smear factor, the formation fluid pressure, and the normal stress on the fault plane into the calculation formula of the vertical connectivity coefficient of the fault, and calculate the vertical connectivity coefficient of the fault at the target location.

[0055] The calculation formula of the vertical connectivity coefficient of the fault is expressed as:

[0056]

[0057] Among them, FPI represents the vertical connectivity coefficient of the fault, dimensionless; P represents the formation fluid pressure, Mpa; σ N represents the normal stress on the fault plane, Mpa; SGR represents the shale smear factor, dimensionless; BI is the brittleness index, dimensionless.

[0058] The shale smear factor is determined by three influencing factors: the thickness of the faulted caprock, the shale content, and the fault throw. The calculation model of the shale smear factor is as Figure 5 shown, and the shale smear factor is expressed as:

[0059]

[0060] where SGR represents the shale smear factor, dimensionless, V sh represents the shale content, D represents the fault throw, ΔZ i represents the thickness of the i-th layer of rock, and n represents the number of layers of the faulted caprock.

[0061] The calculation formula of the brittleness index is as follows:

[0062]

[0063]

[0064]

[0065] where BI is the brittleness index, %; E brit is the normalized Young's modulus, v brit is the normalized Poisson's ratio, E is the Young's modulus of the rock, GPa; E min is the minimum value of the Young's modulus in the formation where the target location is located, E max is the maximum value of the Young's modulus in the formation where the target location is located; v is the Poisson's ratio of the rock, dimensionless, v min is the minimum value of the Poisson's ratio of the rock in the formation where the target location is located, v max is the maximum value of the Poisson's ratio of the rock in the formation where the target location is located. The brittleness index is as Figure 6 shown, Figure 6 in which GR is the natural gamma ray curve, a conventional logging curve that can be used to roughly determine whether a formation at a certain depth is sandstone or shale, and Vsh is the shale content curve.

[0066] By using the oil and gas water data of the drilled wells in the shallow and deep layers near the faulted formations in the oil and gas bearing basin and the oil and gas bearing conditions of the paleo-oil reservoir tracer data, the fault connectivity is identified to obtain the critical area. As Figure 2 shown, the drilling data shows that there are oil and gas accumulations in the formations near the F1 fault and respectively. Then, from the source rock ( and For the faults in this part of the reservoir from the formation to the reservoir, the faults should be in a connected state (the faults at points B, C, D, and E are connected), otherwise oil and gas cannot migrate across layers. There is no oil and gas show and no ancient oil and gas reservoir show above point A, indicating that the oil and gas did not break through point A and continue to migrate upward. Therefore, it is judged that the fault at point A is not connected. Figure 2 Ng in the middle is the Guantao Formation; is the first member of the Dongying Formation; is the second member of the Dongying Formation; is the third member of the Dongying Formation; is the first member of the Shahejie Formation; is the third member of the Shahejie Formation.

[0067] Substitute the influencing factors of point A into the calculation formula of the vertical connectivity coefficient of the fault to obtain the minimum value of the critical region, and substitute the influencing factors of point B into the calculation formula of the vertical connectivity coefficient of the fault to obtain the maximum value of the critical region.

[0068] In this embodiment, the vertical connectivity coefficient of the fault is used to quantitatively characterize the vertical connectivity ability of the fault. The larger the fault connectivity coefficient, the greater the possibility of fault connection. By calculating and counting the connectivity coefficients of the connected points and unconnected points on multiple faults, the critical intervals of connection and non-connection can be given. The critical interval in this embodiment is 0.75 - 2.5. When it is greater than 2.5, the fault is completely connected; when it is less than 0.75, the fault is not connected. Within the interval of 0.75 - 2.5, the greater the connectivity coefficient, the higher the possibility of connection.

[0069] Among them, step 102 specifically includes:

[0070] If the vertical connectivity coefficient of the fault at the target position is greater than the maximum value of the critical region, the target position is predicted to be connected;

[0071] If the vertical connectivity coefficient of the fault at the target position is less than the minimum value of the critical region, the target position is predicted to be unconnected;

[0072] If the vertical connectivity coefficient of the fault at the target position is within the critical region, the target position is predicted to be in an intermediate state.

[0073] The calculation of the normal stress on the fault plane requires the calculation of the three principal stresses. The calculation formula of the three principal stresses is:

[0074]

[0075]

[0076]

[0077] Among them, h is the formation burial depth; ρ(h) is the function of the formation density varying with the formation depth; g is the acceleration of gravity, β1 and β2 are the tectonic stress coefficients in the directions of the maximum and minimum horizontal in-situ stresses respectively; μ is the Poisson's ratio of the rock; α is the Biot coefficient; P is the fluid pressure.

[0078] After determining the triaxial stress and coupling it with the stress square, substitute it into the expression of the normal stress on the fault plane. The expression of the normal stress on the fault plane is:

[0079] σ N =(sinθ1·sinθ2) 2 σ H +(cosθ1·sinθ2) 2 σ h +cosθ2 2 S v ;

[0080] Among them, σ N represents the normal stress on the fault plane, θ1 is the angle between the fault strike and the maximum horizontal principal stress, θ2 is the fault dip angle, σ H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; S v is the vertical principal stress.

[0081] The normal stress on the fault plane is as Figure 3 shown.

[0082] The formation fluid pressure is expressed as:

[0083]

[0084] Among them, P is the formation fluid pressure, S v is the vertical principal stress, P h is the hydrostatic pressure at the depth (h) corresponding to the target position, Δt norm is the acoustic travel time at the target depth corresponding to the target position in the gradient of the normal acoustic travel time varying with depth, that is, Δt norm is the acoustic travel time corresponding to the target depth under the normal compaction of the formation, and Δt is the actual acoustic travel time at the depth corresponding to the target position. The formation fluid pressure is as Figure 4 shown.

[0085] The present invention analyzes the vertical connectivity of the fault based on the vertical connectivity coefficient of the fault and the oil and gas occurrence conditions in the shallow and deep layers near the formation faulted by the fault, as Figure 7 shown.

[0086] For the connectivity of the target area in the undrilled area of the oil and gas bearing basin, first calculate the vertical connectivity coefficients of faults at several set positions within the target area, obtain multiple vertical connectivity coefficients of faults within the entire target area through interpolation, and then obtain the vertical connectivity of faults within the entire target area.

[0087] The prediction method of fault vertical connectivity established by the present invention considering 6 factors affecting fault vertical connectivity, namely the thickness of the faulted caprock, shale content, normal stress on the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw, quantitatively characterizes the fault vertical connectivity in the oil and gas bearing basin. Analyze the fault vertical connectivity based on the vertical connectivity coefficient of the fault and the oil and gas conditions in the shallow and deep layers near the strata faulted by the fault, and then predict the fault vertical connectivity in the undrilled area, which has positive significance for the selection of oil and gas exploration areas and the study of the longitudinal enrichment law of oil and gas in the shallow and deep layers.

[0088] Example 2

[0089] A fault vertical connectivity prediction system in an oil and gas bearing basin provided in this embodiment includes:

[0090] A fault vertical connectivity coefficient determination module, configured to determine the fault vertical connectivity coefficient of the target position according to the influencing factors of the fault vertical connectivity at the target position; the influencing factors include the thickness of the faulted caprock, shale content, normal stress on the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw; the target position is the target position in the undrilled area of the oil and gas bearing basin.

[0091] A vertical connectivity prediction module, configured to predict the vertical connectivity of the target position according to the fault vertical connectivity coefficient of the target position.

[0092] Each embodiment in this specification is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0093] Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, based on the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for predicting the vertical connectivity of faults in an oil and gas bearing basin, characterized in that, Comprising: Determine the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location; the influencing factors include the thickness of the faulted caprock, shale content, normal stress of the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw; the target location is the target location in the un-drilled area of the hydrocarbon-bearing basin; Predict the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location.

2. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 1, wherein, Determine the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location, specifically including: Determine the shale smear factor according to the thickness of the faulted caprock, the shale content, and the fault throw; Substitute the shale smear factor, the formation fluid pressure, and the normal stress of the fault plane into the calculation formula of the vertical connectivity coefficient of the fault, and calculate the vertical connectivity coefficient of the fault at the target location; The calculation formula of the vertical connectivity coefficient of the fault is expressed as: Among them, FPI represents the fault vertical connectivity coefficient, P represents the formation fluid pressure, σ N represents the normal stress of the fault plane, SGR represents the shale smear factor, and BI is the brittleness index.

3. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 2, wherein The shale smear factor is expressed as: Among them, V sh represents the shale content, D represents the fault throw, and ΔZ i represents the thickness of the i-th layer of rock formation, and n represents the number of layers of the faulted caprock.

4. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 2, wherein The brittleness index is expressed as: Among them, E brit is the normalized Young's modulus, and v brit is the normalized Poisson's ratio.

5. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 1, wherein Predict the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location, specifically including: If the vertical connectivity coefficient of the fault at the target location is greater than the maximum value of the critical region, the target location is predicted to be connected; If the vertical connectivity coefficient of the fault at the target location is less than the minimum value of the critical region, the target location is predicted to be unconnected; If the vertical connectivity coefficient of the fault at the target location is within the critical region, the target location is predicted to be in an intermediate state.

6. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 1, wherein, The normal stress of the fault plane is expressed as: σ N =(sinθ1·sinθ2) 2 σ H +(cosθ1·sinθ2) 2 σ h +cosθ2 2 S v ; Among them, σ N represents the normal stress of the fault plane, θ1 is the angle between the fault strike and the maximum horizontal principal stress, θ2 is the dip angle of the fault plane, σ H is the maximum horizontal principal stress; σ h is the minimum horizontal principal stress; S v is the vertical principal stress.

7. The method for predicting the vertical connectivity of faults in an oil and gas bearing basin according to claim 1, characterized in that, The formation fluid pressure is expressed as: Among them, P is the formation fluid pressure, and S v is the vertical principal stress, and P h is the hydrostatic pressure at the depth corresponding to the target position, and △t norm is the acoustic travel time at the depth corresponding to the target position in the gradient of the normal acoustic travel time varying with depth, and △t is the actual acoustic travel time at the depth corresponding to the target position.

8. A prediction system for vertical connectivity of faults in an oil and gas bearing basin, characterized in that, Comprising: A vertical connectivity coefficient determination module for determining the vertical connectivity coefficient of the fault at the target location according to the influencing factors of the vertical connectivity of the fault at the target location; the influencing factors include the thickness of the faulted caprock, shale content, normal stress of the fault plane, formation fluid pressure, brittleness degree of the caprock, and fault throw; the target location is the target location in the un-drilled area of the hydrocarbon-bearing basin; A vertical connectivity prediction module for predicting the vertical connectivity of the target location according to the vertical connectivity coefficient of the fault at the target location.

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