CN112945829A - Method and system for analyzing water drive residual oil of tight sandstone reservoir - Google Patents
Method and system for analyzing water drive residual oil of tight sandstone reservoir Download PDFInfo
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Abstract
The invention discloses a method and a system for analyzing water drive residual oil of a tight sandstone reservoir, wherein the method comprises the following steps: performing logical operation on the water phase of the core scanning slice in the water flooding process to obtain the water-oil spatial distribution in different water flooding states; establishing a water-drive residual oil analysis model based on curve similarity by using water-oil spatial distribution under different water-drive states to obtain fluid distribution difference in a core pore space; analyzing the distribution characteristics of the residual oil in the rock core sample according to the fluid distribution difference in the rock core pore space; and predicting the recovery ratio of the oil reservoir by using the distribution characteristics. The water-drive residual oil analysis method provided by the invention is based on the digital core, the formation mechanism and the dynamic change process of the residual oil are quantitatively analyzed from the pore size, and the oil reservoir evaluation precision and the oil reservoir recovery ratio can be improved.
Description
Technical Field
The invention belongs to the field of unconventional oil and gas reservoir evaluation and digital rock physics, and particularly relates to a method and a system for analyzing water-drive residual oil of a tight sandstone reservoir.
Background
Crude oil is one of the important energy sources, and advanced and low-cost development technologies are increasingly required to improve the recovery efficiency of oil reservoirs. The enhanced oil recovery technology based on water flooding is a common production increasing mode, but the investment cost is generally high, so that the mobility and distribution characteristics of oil need to be described by adopting a petroleum engineering method and numerical simulation, and the development scheme can be reasonably designed only by carrying out historical simulation and prediction on an oil reservoir. However, because the pore structure of the tight sandstone reservoir and the micro-distribution of oil are complex, the conventional microscopic observation is not enough to truly describe the internal structure of the core, and other technologies (X-ray computed tomography) are needed to perform quantitative and fine description on a micro scale. In 1991, X-ray computed tomography (X-CT) technology was beginning to be used for porous media analysis, which can provide non-destructive images at the micro-to nano-scale, enabling micro-scale analysis, and is one of the important methods for reservoir research.
In recent years, researchers perform X-CT scanning on a real core to obtain an image and reconstruct a core pore structure, can analyze reservoir characteristics, perform seepage simulation, improve the research of the recovery ratio and the like. By combining an image processing method, the distribution of different fluids in the rock core can be extracted by an X-CT scanning technology, and Geistlinger and the like research the pore structure and the fluid distribution of the rock core under different states. Iglauer et al studied the pattern of liquid colonization in the real core sample and the amount thereof by this technique. Qiang Lei et al studied the distribution of residual oil in different flow regimes. Senyou An et al quantitatively calculated the volume of remaining oil on An in situ displacement basis and classified in combination with shape factors.
However, the above studies on the residual oil were mainly performed from a qualitative point of view, and no quantitative analysis was performed on the water flooding residual oil. Thereby making reservoir predictions inaccurate and incomplete.
Disclosure of Invention
The invention aims to provide a method and a system for analyzing water-drive residual oil of a compact sandstone reservoir, which are used for observing and analyzing the formation process and mechanism of the residual oil on a pore scale level and provide a research method for the research of a micro-seepage mechanism in the oil reservoir development process.
In order to realize the purpose, the following technical scheme is adopted:
a method for analyzing water drive residual oil of a tight sandstone reservoir comprises the following steps:
performing logical operation on the water phase of the core scanning slice in the water flooding process to obtain the water-oil spatial distribution in different water flooding states;
establishing a water-drive residual oil analysis model based on curve similarity by using water-oil spatial distribution under different water-drive states to obtain fluid distribution difference in a core pore space;
analyzing the distribution characteristics of the residual oil in the rock core sample according to the fluid distribution difference in the rock core pore space; and predicting the recovery ratio of the oil reservoir by using the distribution characteristics.
Further, a CT scanning technology is adopted to obtain a core scanning slice in the water flooding process.
Further, the core scanning slice comprises a dry sample slice, a saturated water slice, a saturated oil slice and a residual oil slice.
Further, a water flooding residual oil analysis model is established based on the curve similarity, and the method specifically comprises the following steps:
carrying out data normalization on the water-oil spatial distribution;
establishing a normalized frequency accumulation distribution curve of water-oil spatial distribution;
and constructing a water drive residual oil analysis model based on curve similarity from three aspects of the total change trend of the movable oil, the relation between the pore diameter and the movable oil and the relative distribution of the residual oil by taking a frequency cumulative distribution curve of the water-oil spatial distribution as an object.
Further, firstly, carrying out data standardization on water-oil spatial distribution; on the basis of normalized data, the water flooding residual oil analysis model comprises the following steps: the general trend is used for describing the oil displacement efficiency and the general change of the movable oil by combining the saturation; the degree of expansion and contraction is used for describing the relation between the movable oil and the aperture; the amount of translation is used to describe the relative distribution of the remaining oil in the different pores.
Further, a specific method for performing data normalization on water-oil spatial distribution is as follows:
in the formula ：xiFor the data to be normalized, i belongs to (1, n), n is the number of samples, yiTo normalize the post-data, Xmax and XminThe actual range of the pore diameter is,
and
is a normalized data range.
Further, the general change trend of movable oil in the core during the displacement process is calculated according to the following formula:
wherein i is a sampling point of the pore radius, n is the total number of sampling points,
is the cumulative value of the distribution corresponding to the ith sampling point in the reference curve,
is the distribution accumulated value, y, corresponding to the ith sampling point in the curve to be evaluatedirIs the aperture coordinate.
Further, the degree of expansion and contraction E ═ E (E) of the amount of change in the movable oil in the range of different pore diameters was calculated by the following equation1,...,ej,...,ek)：
wherein ,
and
the maximum value and the minimum value of the jth reference curve,
and
and k is the number of segments.
Further, the degree of translation is calculated as follows:
wherein m is the number of pore parameter samples in the segmentation interval, N is the number of segments,
and
the cumulative value of the distributed frequencies is in the jth interval and is the radius value corresponding to the ith large value.
A system for the tight sandstone reservoir water flooding residual oil analysis method, comprising:
the water-oil spatial distribution calculation module is used for performing logical operation on the water phase of the core scanning slice in the water flooding process to obtain water-oil spatial distribution in different water flooding states;
the analysis model establishing module is used for establishing a water drive residual oil analysis model based on curve similarity by utilizing water-oil spatial distribution under different water drive states to obtain fluid distribution difference in a core pore space;
the residual oil analysis module is used for describing the distribution characteristics of residual oil in the core sample in the displacement process according to the fluid distribution difference in the core pore space; and utilizing the distribution characteristics to predict the oil reservoir.
The invention has the following beneficial effects:
the invention provides a complete digital core-based water-drive residual oil analysis method, which is used for quantitatively analyzing a residual oil formation mechanism and a dynamic change process from a pore size and can improve the oil reservoir evaluation precision and the oil reservoir recovery ratio.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a core scan slice; (a) dry sample, (b) saturated oil, (c) residual oil.
FIG. 2 is a diagram of oil-water space data volumes in different states; (a) dry sample, (b) saturated oil, (c) residual oil.
FIG. 3 is a cumulative probability curve of pore distribution under different conditions (dry sample, saturated oil, remaining oil).
Fig. 4 is a water flooding remaining oil analysis model.
Fig. 5 is a calculation result of a water flooding residual oil analysis model.
Detailed Description
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The following detailed description is exemplary in nature and is intended to provide further details of the invention. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention.
The embodiment of the invention provides a method and a system for analyzing water drive residual oil of a tight sandstone reservoir, wherein the method comprises the following steps: obtaining a core scanning slice in the water flooding process; performing logical operation on the water phase of the core scanning slice to obtain the water-oil spatial distribution under different water flooding states; establishing a water-drive residual oil analysis model based on curve similarity by utilizing water-oil spatial distribution under different water-drive states, and calculating the water-drive residual oil analysis model to obtain fluid distribution difference in a core pore space; and analyzing the distribution characteristics of the residual oil in the core sample in the displacement process according to the calculation result of the model, and predicting the oil reservoir by using the distribution characteristics.
The following is set forth with reference to specific examples, which include two parts of experiments and waterflood residual oil analysis:
1. experiment of
By taking 7 long segments of sandstone in the Huaqing area of the Ordos basin as a research object and adopting an in-situ displacement scanning technology, the dynamic change characteristics of oil in the water flooding process are deeply analyzed. A cylindrical sample (the diameter is 3.0mm, the length is 5.0mm) is drilled, a core is subjected to a displacement experiment by adopting an in-situ CT displacement system, scanning is carried out by combining Zeiss submicron CT (510VERSA) (the scanning voltage is 70KV, the power is 5W, the objective lens is 4 times, the scanning resolution is 3.32 mu m), the size of a reconstructed three-dimensional data body is 1004 x 1005, the imaging capability of water is improved by taking 10% potassium iodide as a solution, the confining pressure in displacement is 2.0MPa, and a microscopic displacement pump uses a constant-pressure mode. The specific experimental steps are as follows:
(1) and (4) firstly carrying out oil washing and salt washing treatment on the drilled rock core.
(2) Original dry core CT scanning: and (3) loading the rock core into a rock core holder, fixing the rock core holder on a CT device, and scanning for 10 hours.
(3) Saturated water: vacuumizing, self-sucking saturated water, injecting water solution by using a displacement pump to obtain a saturated water core, and scanning for 10 hours.
(4) Saturated oil: simulated oil was injected into the bound water phase to obtain a saturated oil sample, which was scanned for 14 hours.
(5) Residual oil: the saturated oil sample was subjected to a water flooding experiment to bound oil state and scanned for 14 hours.
(6) Data extraction, processing and three-dimensional model reconstruction: preprocessing the CT image by adopting non-local mean filtering (Buads), dividing rock core pores, an oil phase and a water phase by using a watershed algorithm, constructing a three-dimensional network model, and calculating the porosity and the pore radius.
And (3) obtaining a core scanning slice in the water flooding process by adopting a CT scanning technology, and referring to figure 1. Based on the different attenuation laws of the X-ray when penetrating different materials, the dark gray scale range below the threshold value in the dry sample slice corresponds to the pores, and the light gray scale range above the threshold value in the saturated oil and the residual oil slice corresponds to the water.
And performing logical operation on the extracted water phase in the dry sample pores, saturated water and residual oil states to obtain the water-oil spatial distribution in different water flooding states, which is shown in figure 2.
2. Water drive residual oil analysis model
On the basis of obtaining the digital core, a water-drive residual oil analysis model is calculated and established based on curve similarity, the fluid distribution difference in the core pore space in different states in the water flooding process is calculated, and the distribution characteristics of residual oil in the core sample in the flooding process are analyzed according to the calculation result of the water-drive residual oil analysis model.
2.1 analytical model
And (3) measuring the pore radius of the dry sample of the rock core and the occurrence space of oil (saturated oil and residual oil) in different displacement states, and calculating a probability accumulation curve of the dry sample of the rock core, which is shown in figure 3. In fig. 3, the trends of the three curves are the same, but the curves have different degrees of difference, and the occurrence rules of the oil in different pores are different under different reaction states. In this embodiment, based on the curve similarity, the general trend, the translation degree, and the expansion degree are used as similarity evaluation indexes, and a residual oil analysis model is established as shown in fig. 4.
2.2 data Specification
In order to realize quantitative analysis and comparison of rock cores of different areas and different reservoirs, firstly, data normalization is carried out on water-oil spatial distribution, and the formula is (1):
equation (1) achieves pore radius normalization, where xiFor the data to be normalized, i belongs to (1, n), n is the number of samples, yiTo normalize the post-data, Xmax and XminThe actual range of the pore diameter is,
and
is a normalized data range. The occurrence space of the oil phase is changed under different states in the oil-water flooding process, so that the aperture of a dry sample is taken as a standard reference. The aperture range of the dry sample in this embodiment is 3.38um-810um, so Xmin and XmaxFixed to 3.38um and 810um, provided
2.3 general trends
Ideally the pores in the core are saturated with oil and the oil can be completely displaced. Since the pore space and the cumulative trend of the probability of the oil occurrence space distribution curves in different states (saturated oil and residual oil) are the same, the present embodiment uses the distribution curve corresponding to the dry sample as a reference curve, and other curves as the curves to be evaluated, and the general trend is calculated by the formula (2).
Wherein i is a sampling point of the pore radius, n is the total number of sampling points,
is the cumulative value of the distribution corresponding to the ith sampling point in the reference curve,
is the distribution accumulated value, y, corresponding to the ith sampling point in the curve to be evaluatedirIs the aperture coordinate.
2.4 degree of stretchability
The pore radius range is segmented by means of dispersion marksStandardizing thought, describing the transverse expansion ratio of each section by referring to the minimum difference, and calculating the expansion degree E (E) under different aperture ranges according to the formula (3)1,...,ej,...,ek)。
wherein ,
and
the maximum value and the minimum value of the jth reference curve,
and
the maximum and minimum values of the curve to be evaluated in the j-th segment are shown, k is the number of segments, 0.01 is added to the denominator to prevent the denominator from being 0, and the segment step length of the embodiment is 10 μm.
2.5 measurement of translation
To describe the relative distribution of the remaining oil in the different pores, the degree of translation was calculated as follows:
wherein m is the number of pore parameter samples in the segmentation interval, N is the number of segments,
and
the cumulative value of the distributed frequencies is in the jth interval and is the radius value corresponding to the ith large value. This embodiment takes 10% as the segmentation step, so N is 10.
2.6 core sample analysis
And obtaining the calculation results of the general trend, the expansion degree and the translation degree based on the curve similarity, and the figure 5. Wherein, the dry sample-saturated oil and the dry sample-residual oil are both taken as reference curves.
From fig. 5(a), the general trend difference between the oil phase in the dry sample and the saturated oil is 33, which shows that the saturated oil is more in the large pore space, and the existence of the pore space not filled with oil in the rock core of the saturated oil due to the end of the pore or the throat is explained again by combining fig. 2. The general trend difference between the dry sample and the residual oil is 26, which shows that the oil in the large pores is partially removed after oil displacement, so that the proportion of the oil in the small pores is improved.
As can be seen from FIG. 5(b), the pore diameter range is 60 μm-70 μm, the minimum expansion value is obtained, the corresponding actual core pore diameter is 51 μm-59 μm according to the inverse process calculation of the formula (1), which indicates that the oil change in the pores with the radius of 51 μm-59 μm is large in the oil displacement process; in the pores with the radius larger than 210 μm (actually 172) or smaller than 10 μm (actually 10.64 μm), the expansion value approaches to 0, which indicates that the amount of change of the oil is very small, and also reflects that the oil in the large-sized pores in the experimental sample of this embodiment is not easily removed and the oil in the small-sized pores cannot be filled.
As can be seen from fig. 5(c), the minimum translation degree of saturated oil is-17.55 compared with the dry sample, which indicates that the curve is shifted to the right side, and the corresponding oil is more distributed in the macropores, mainly because the small pores in the core are easy to block and cannot be filled with oil; the residual oil translation degree is-12.55, the curve is shifted to the right side, and the shift degree is lower than that of saturated oil, which indicates the displacement effect on oil in large pores.
In the embodiment, an Ordos basin long 7 compact sandstone is taken as a research object, a water flooding experiment is carried out on a sample by adopting an in-situ displacement scanning technology, a digital core is extracted to observe the dynamic law of the existing oil in the displacement process, and a water flooding residual oil analysis method is established by combining an image processing technology and curve similarity. (1) And extracting a digital core based on in-situ displacement scanning, observing the dynamic rule of the existing oil in the water flooding process, quantitatively calculating the oil saturation and the water saturation, and calculating the probability cumulative distribution of the pore diameter of the core and the radius of the existing oil. (2) And establishing a residual oil analysis model by combining the curve similarity: the oil displacement efficiency and the general variation trend of the movable oil are analyzed by the general trend, the relation between the movable oil and the pore size is analyzed by the flexibility, and the relative distribution of the residual oil in different pores is analyzed by the translation amount. Meanwhile, a data normalization method is provided, and the generalization capability of the evaluation method is improved. (3) And describing and analyzing the movement change rate of the oil in different apertures and the spatial distribution difference of the residual oil in the displacement process according to the calculation result. The method further explains the dynamic change rule of the preserved oil in the displacement process on the basis of calculating the pore space and oil distribution in the rock core, and provides a quantifiable comparative analysis method for reservoir research in the same region.
It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.
Claims (10)
1. A method for analyzing water drive residual oil in a tight sandstone reservoir is characterized by comprising the following steps:
performing logical operation on the water phase of the core scanning slice in the water flooding process to obtain the water-oil spatial distribution in different water flooding states;
establishing a water-drive residual oil analysis model based on curve similarity by using water-oil spatial distribution under different water-drive states to obtain fluid distribution difference in a core pore space;
analyzing the distribution characteristics of the residual oil in the rock core sample according to the fluid distribution difference in the rock core pore space; and predicting the recovery ratio of the oil reservoir by using the distribution characteristics.
2. The tight sandstone reservoir water flooding residual oil analysis method of claim 1, wherein a CT scanning technology is adopted to obtain core scanning slices in the water flooding process.
3. The tight sandstone reservoir water flooding residual oil analysis method of claim 2, wherein the core scan slice comprises a dry sample slice, a saturated water slice, a saturated oil slice, and a residual oil slice.
4. The tight sandstone reservoir water flooding residual oil analysis method of claim 1, wherein the establishing of the water flooding residual oil analysis model based on curve similarity specifically comprises:
carrying out data normalization on the water-oil spatial distribution;
establishing a normalized frequency accumulation distribution curve of water-oil spatial distribution;
and constructing a water drive residual oil analysis model based on curve similarity from three aspects of the total change trend of the movable oil, the relation between the pore diameter and the movable oil and the relative distribution of the residual oil by taking a frequency cumulative distribution curve of the water-oil spatial distribution as an object.
5. The tight sandstone reservoir water drive residual oil analysis method of claim 4, wherein the data normalization is performed on the water-oil spatial distribution; on the basis of normalized data, the water flooding residual oil analysis model comprises the following steps: the general trend is used for describing the oil displacement efficiency and the general change of the movable oil by combining the saturation; the degree of expansion and contraction is used for describing the relation between the movable oil and the aperture; the amount of translation is used to describe the relative distribution of the remaining oil in the different pores.
6. The tight sandstone reservoir water drive residual oil analysis method of claim 4, wherein the concrete method for performing data normalization on the water-oil spatial distribution is as follows:
in the formula ：xiFor the data to be normalized, i belongs to (1, n), n is the number of samples, yiTo normalize the post-data, Xmax and XminThe actual range of the pore diameter is,
and
is a normalized data range.
7. The tight sandstone reservoir water flooding residual oil analysis method of claim 4, wherein the general change trend of movable oil in the core during the displacement process is calculated according to the following formula:
wherein i is a sampling point of the pore radius, n is the total number of sampling points,
is the cumulative value of the distribution corresponding to the ith sampling point in the reference curve,
is the distribution accumulated value, y, corresponding to the ith sampling point in the curve to be evaluatedirIs the aperture coordinate.
8. The tight sandstone reservoir water-flooding residual oil analysis method of claim 4, wherein the degree of expansion E-of the variable quantity of the movable oil in different pore size ranges is calculated according to the following formula (E-E)1,...,ej,...,ek)：
wherein ,
and
the maximum value and the minimum value of the jth reference curve,
and
and k is the number of segments.
9. The tight sandstone reservoir water-drive residual oil analysis method of claim 4, wherein the translation degree is calculated according to the following formula:
wherein m is the number of pore parameter samples in the segmentation interval, N is the number of segments,
and
the cumulative value of the distributed frequencies is in the jth interval and is the radius value corresponding to the ith large value.
10. A system for the tight sandstone reservoir water flooding residual oil analysis method of claim 1, comprising:
the water-oil spatial distribution calculation module is used for performing logical operation on the water phase of the core scanning slice in the water flooding process to obtain water-oil spatial distribution in different water flooding states;
the analysis model establishing module is used for establishing a water drive residual oil analysis model based on curve similarity by utilizing water-oil spatial distribution under different water drive states to obtain fluid distribution difference in a core pore space;
the residual oil analysis module is used for describing the distribution characteristics of residual oil in the core sample in the displacement process according to the fluid distribution difference in the core pore space; and utilizing the distribution characteristics to predict the oil reservoir.
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