CN110927819A - Crack development degree characterization method - Google Patents
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- CN110927819A CN110927819A CN201811105953.9A CN201811105953A CN110927819A CN 110927819 A CN110927819 A CN 110927819A CN 201811105953 A CN201811105953 A CN 201811105953A CN 110927819 A CN110927819 A CN 110927819A
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Abstract
The invention discloses a crack development degree characterization method, which comprises the following steps: determining the calculation step length of the fracture strength by adopting a high-resolution sequence stratigraphy method, wherein the calculation step length value is the deposition cycle thickness close to the seismic data identification precision; acquiring basic crack parameters including the number of cracks and crack inclination angles; quantitatively calculating the crack line density and the crack apparent cutting ratio by adopting a fixed-step and windowing method, wherein the crack line density is the ratio of the number of cracks in the calculated step length to the calculated step length, and the crack apparent cutting ratio is the ratio of the sum of tangent values of the inclination angles of the cracks in the calculated step length to the calculated step length; and characterizing the development degree of the fracture of the single-well core well section according to the fracture line density and the fracture apparent cutting ratio. On the basis of research on a high-resolution sequence stratigraphic method, the definition of the length of a straight line in the density of the fracture line is perfected by clearly calculating the step length, and the difference of the development degree of the fracture caused by the difference of the dip angle of the fracture is solved by adopting the quantitative characterization of the apparent cutting ratio of the fracture.
Description
Technical Field
The invention relates to the technical field of crack research, in particular to a crack development degree characterization method.
Background
The accurate characterization of the crack development degree is a basic link and an important link in the crack research, the result of the link directly influences the conclusion of the follow-up work of the crack research, the established characterization method and standard must have the principles of analogy, prediction and quantification, and the accurate and effective characterization of the crack development strength has important significance for the crack research.
How to accurately characterize fracture development degree is not determined, and different students propose different evaluation schemes or standards of fracture development degree according to the development characteristics and evaluation parameters of field outcrop, rock core and imaging logging fractures in a research area (such as Narr et al, 1984; Van Golf-Racht et al, 1989; Ruhland et al, 1989; monowaysia et al, 1997; serpins et al, 2004; Wangzhua et al, 2007; Wenxui et al, 2003, 2009; small cattle et al, 2014; Liuge cloud et al, 2015). Wherein Van Golf-Racht et al (1989) provides a crack density index, and respectively provides general expressions of crack body density, crack surface density and crack line density; ruhland et al (1989) define the fracture strength of high angle fractures as the ratio of fracture frequency to formation frequency; the fracture spacing index, the ratio of formation thickness to fracture spacing, as proposed by Narr et al (1984), Mono Var et al (1997); yuanshiyi et al (2004) and Wangzhenhua et al (2007) propose to evaluate the degree of crack development by grading the crack length and opening; zhongxingui et al (2003, 2009) proposed an evaluation index of the degree of development of the tight sandstone fracture in the region along the river gulf in the Ordos basin according to the distribution range of the linear density of the structural fracture; and (3) the Liuge cloud (2015) provides a fracture cutting ratio index to represent the longitudinal development strength of the high-angle fracture, and the fracture cutting ratio index is a ratio of the total fracture depth of the sandstone core segment to the total thickness of the rock stratum.
Currently, the extent of fracture development is generally characterized by a fracture line density, which is defined as: and generally refers to the ratio of the number of fractures intersecting a straight line perpendicular to the flow direction or the centerline of the core to the length of the straight line. However, the length of a straight line is not defined, the straight line is a certain lithology, a well section (core section) to be measured, the fixed length or the whole stratum, and meanwhile, the difference of the fracture development degree caused by the difference of the fracture inclination angle is not represented by a quantitative parameter all the time, so that the establishment of a rock stratum fracture development degree system is directly influenced, an accurate guide reference cannot be provided for the exploration and development of the oil and gas field, and the adverse influence is brought to the deep research of the exploration and development of the oil and gas field.
Disclosure of Invention
The invention aims to overcome the defects that a scientific and complete fracture development degree system is not established in the prior art, and accurate guide reference cannot be provided for the exploration and development of oil and gas fields, so that adverse effects are brought to the deep research of the exploration and development of the oil and gas fields, and provides a fracture development degree characterization method, so that the fracture can be characterized in an analogized, predictable and quantitative manner.
In order to achieve the above purpose, the invention provides the following technical scheme:
a fracture development degree characterization method, comprising the following steps:
the method comprises the following steps: determining the calculation step length of the fracture strength by adopting a high-resolution sequence stratigraphy method, wherein the calculation step length value is the deposition cycle thickness close to the seismic data identification precision;
step two: acquiring basic fracture parameters, wherein the basic fracture parameters comprise the number of fractures and fracture inclination angles;
step three: quantitatively calculating crack line density and crack apparent cutting ratio by adopting a fixed-step and windowing method, wherein the crack line density is the ratio of the number of cracks in the calculated step length to the calculated step length, and the crack apparent cutting ratio is the ratio of the sum of tangent values of the inclination angles of the cracks in the calculated step length to the calculated step length;
step four: and characterizing the development degree of the fracture of the single-well core well section according to the fracture line density and the fracture apparent cutting ratio.
Preferably, in the first step, short-period gyrus are identified on the basis of high-resolution sequence stratigraphic division, a single forward gyrus or reverse gyrus is represented in combination to obtain a first interval range of deposition gyrus thickness, an identifiable longitudinal precision minimum value is obtained according to the geophysical seismic data resolution, and finally the thickness closest to the longitudinal precision minimum value in the first interval range is taken as a calculation step length.
Preferably, in the second step, the fracture basic parameters further include depth, type, inclination, opening, length and width, and these parameters can assist in the research of the fracture development degree and can also be further used as check data.
Preferably, in the second step, the fracture basic parameters are obtained according to the rock core, the outcrop and the imaging logging.
Preferably, in the second step, the fracture basic parameters are obtained from imaging logging, and auxiliary correction is performed through core and outcrop measurement.
Preferably, in the third step, the selection of the window is based on the imaging log section.
Preferably, the third step is to movably set a plurality of windows, so that the cracks are movably identified, the identification precision is higher, and missing identification is avoided.
Preferably, in the fourth step, the fracture development degree characterization result of the research area is divided into three stages, which are respectively:
when the crack line density is more than 0.15 and the apparent cutting ratio of the crack is more than 0.1, the crack develops at a high angle;
when the density of the crack lines is more than 0.15 and the apparent cutting ratio of the crack is less than 0.1, the crack develops at a low angle;
when the density of the crack lines is less than 0.15, cracks are underdeveloped.
Compared with the prior art, the invention has the beneficial effects that:
the crack development degree characterization is an important basis for developing research on main control factors of crack development in a research area and quantitative prediction of cracks, and the method perfects the definition of the linear length in the density of the crack lines by clearly calculating the step length on the basis of research on a high-resolution sequence stratigraphic method, quantitatively characterizes the longitudinal strength of the cracks by adopting the crack apparent cutting ratio, and solves the problem of crack development degree difference caused by crack inclination angle difference. The method for determining the step length and windowing can realize analogized, predictable and quantitative characterization of crack development degrees, and solves the defect of inconsistent crack characterization of different regions and different layer systems, and belongs to the first application in crack development degree characterization. The crack development degree characterization system is established, scientific and accurate guidance reference can be provided for the exploration and development of the oil and gas field, and therefore research and analysis of the exploration and development of the oil and gas field can be promoted; the method is not influenced by the lithology and thickness of the stratum, has good popularization and has important significance for crack research.
Description of the drawings:
FIG. 1 is a schematic flow chart of a fracture development degree characterization method according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to test examples and specific embodiments. It should be understood that the scope of the above-described subject matter is not limited to the following examples, and any techniques implemented based on the disclosure of the present invention are within the scope of the present invention.
As shown in fig. 1, a fracture development degree characterization method includes the following steps:
the method comprises the following steps: and determining the calculation step length of the fracture strength by adopting a high-resolution sequence stratigraphy method, wherein the calculation step length value is the deposition cycle thickness close to the seismic data identification precision.
The method takes the deposition cycle thickness close to the seismic data identification precision as the fracture strength calculation fixed step length based on the sequence stratigraphy research, avoids the calculation thickness from being non-uniform, and has the advantages of analogism and predictability.
Since the high-resolution sequence stratigraphic theory comes out, strong reverberation and high attention are drawn to the petroleum geology and sedimentary geology by brand-new concepts and technical methods and actual application effects thereof. In recent years, a plurality of research results of Chinese scientists show that the theoretical system and the technical method thereof are more suitable for analyzing the stratigraphic sequence of the continental facies basin compared with the typical stratigraphic sequence theory of P.R.Vall, and have wide application prospect in the geological research of the exploration and development engineering of oil and gas reservoirs.
The short-period gyrocompass is a minimum-cause sequence unit divided according to data such as earth surface bedrock outcrop, well drilling rock core, well logging and the like. The top-bottom interface of the sequence is a small scouring surface or an intermittent exposed surface formed when the short-period reference surface descends to the lowest point, and can also be a discontinuous surface or an entire interface formed by under-compensation or no deposition during the ascending and descending period of the reference surface.
The method identifies short-period gyroids on the basis of high-resolution sequence stratigraphic division, and the short-period gyroids are combined to be a single forward gyroid or a single reverse gyroid to obtain a first interval range (60m-100m) of the thickness of the deposition gyroid.
Seismic data resolution is always calculated by a series of wavelength values given by the quotient of wave speed and frequency. There are two limits to the vertical resolution, both derived from the interaction of the wavelets reflected by two adjacent interfaces, the separable limit being equal to a quarter of a wavelength, according to which the longitudinal resolution recognizable by the study area is 55 m.
And integrating the high-resolution sequence stratum research and the three-dimensional seismic longitudinal recognition precision of the research area, and determining the calculation step length of the crack strength of the research area to be 60 m.
Step two: the method comprises the steps of obtaining basic fracture parameters according to a rock core, an outcrop and an imaging logging, wherein the basic fracture parameters comprise the number of fractures and fracture inclination angles, and further comprise depth, type, inclination, openness, length and width, and the basic fracture parameters can assist in researching the development degree of the fracture and can also be further used as check data. The basic parameters of the fracture come from imaging logging and are corrected in an auxiliary mode through core and outcrop measurement.
Step three: the method adopts a fixed-step length and windowing method to quantitatively calculate the fracture line density and the fracture apparent cutting ratio, the selection of the windows is based on the imaging well logging section, a plurality of windows can be movably arranged, the fractures can be movably identified, the identification precision is higher, and the identification omission is avoided. The crack line density is the ratio of the number of cracks in the calculation step length to the calculation step length,
the apparent fracture cutting ratio is the ratio of the sum of tangent values of the inclination angles of the fractures in the calculation step length to the calculation step length,
where θ is the fracture dip, n is the number of fractures, D is the borehole diameter, and is a fixed value for a single well, and D is 30cm for the area of investigation.
Step four: according to the fracture line density and the fracture apparent cutting ratio, the fracture development degree of the single-well coring well section is represented, and the fracture development degree representation result of the research area is divided into three stages, namely:
when the crack line density is more than 0.15 and the apparent cutting ratio of the crack is more than 0.1, the crack develops at a high angle;
when the density of the crack lines is more than 0.15 and the apparent cutting ratio of the crack is less than 0.1, the crack develops at a low angle;
when the density of the crack lines is less than 0.15, cracks are underdeveloped.
Comparing the single well test result with the actually measured physical properties, the finding shows that the high-angle seam development and the low-angle seam development can obtain a high-yield and relatively high-permeability high-quality reservoir, but the high-angle seam development is obviously superior to that of the low-angle seam development reservoir, which indicates that the method has objective verification applicability in a research area.
The above embodiments are only used for illustrating the invention and not for limiting the technical solutions described in the invention, and although the present invention has been described in detail in the present specification with reference to the above embodiments, the present invention is not limited to the above embodiments, and therefore, any modification or equivalent replacement of the present invention is made; all such modifications and variations are intended to be included herein within the scope of this disclosure and the appended claims.
Claims (8)
1. A fracture development degree characterization method is characterized by comprising the following steps:
the method comprises the following steps: determining the calculation step length of the fracture strength by adopting a high-resolution sequence stratigraphy method, wherein the calculation step length value is the deposition cycle thickness close to the seismic data identification precision;
step two: acquiring basic fracture parameters, wherein the basic fracture parameters comprise the number of fractures and fracture inclination angles;
step three: quantitatively calculating crack line density and crack apparent cutting ratio by adopting a fixed-step and windowing method, wherein the crack line density is the ratio of the number of cracks in the calculated step length to the calculated step length, and the crack apparent cutting ratio is the ratio of the sum of tangent values of the inclination angles of the cracks in the calculated step length to the calculated step length;
step four: and characterizing the development degree of the fracture of the single-well core well section according to the fracture line density and the fracture apparent cutting ratio.
2. The method for characterizing the development degree of the fracture as claimed in claim 1, wherein in the first step, the short-period gyrus are identified on the basis of high-resolution sequence stratigraphic division, and the short-period gyrus are combined to be a single forward gyrus or reverse gyrus to obtain a first interval range of the thickness of the deposition gyrus, then an identifiable longitudinal precision minimum value is obtained according to the resolution of geophysical seismic data, and finally the thickness closest to the longitudinal precision minimum value in the first interval range is taken as the calculation step length.
3. The method for characterizing the development degree of a fracture according to claim 1, wherein in the second step, the basic fracture parameters further include depth, type, inclination, opening, length and width.
4. The method for characterizing the development degree of the fracture according to claim 1, wherein in the second step, the fracture basic parameters are obtained according to core, outcrop and imaging logging.
5. The method for characterizing the development degree of the fracture as claimed in claim 4, wherein in the second step, the fracture basic parameters are from imaging logging and are corrected by core and outcrop measurement.
6. The method for characterizing the development degree of a fracture as claimed in claim 1, wherein in the third step, the window is selected based on the imaging log section.
7. The method for characterizing the development degree of a fracture according to claim 6, wherein the third step is to open a plurality of windows.
8. The method for characterizing the development degree of cracks according to any one of claims 1 to 7, wherein in the fourth step, the characterization results of the development degree of cracks in the research area are divided into three stages, which are respectively:
when the crack line density is more than 0.15 and the apparent cutting ratio of the crack is more than 0.1, the crack develops at a high angle;
when the density of the crack lines is more than 0.15 and the apparent cutting ratio of the crack is less than 0.1, the crack develops at a low angle;
when the density of the crack lines is less than 0.15, cracks are underdeveloped.
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