CN114047547A - Quantitative evaluation method for sealing capacity of gypsum-rock cover layer - Google Patents
Quantitative evaluation method for sealing capacity of gypsum-rock cover layer Download PDFInfo
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Abstract
The invention relates to a quantitative evaluation method for sealing capacity of a paste rock cover layer, which comprises the following steps: selecting lithology combination types, lithology partitions, dominant lithology accumulated thickness, cover layer accumulated thickness, maximum thickness of a thick single layer and a cover-to-ground ratio as evaluation parameters; taking the closure capacity of the cover layer as a decision target, taking the lithology and the thickness as intermediate elements, taking the evaluation parameters as alternative schemes, establishing a hierarchical structure model in AHP software, analyzing the model to generate a judgment matrix, and judging the evaluation parameters by the judgment matrix to obtain the weight values of the evaluation parameters; describing and quantifying each evaluation parameter by adopting a fuzzy language to obtain each evaluation parameter assignment; and establishing a quantitative evaluation model by using a weighted average method according to the weighted values and the assignments of the evaluation parameters, and evaluating the sealing capacity of the gypsum rock cover layer according to a comprehensive evaluation value C calculated by the quantitative evaluation model. The method can accurately judge the sealing capacity of the paste rock cover layer, and has the advantages of high precision, simplicity, feasibility and wide application range.
Description
Technical Field
The invention belongs to the technical field of oil-gas exploration, relates to a technology of oil-gas exploration of a paste rock cover layer, and particularly relates to a quantitative evaluation method for sealing capacity of the paste rock cover layer.
Background
The gypsum rock is used as the top-quality cover layer and is very important for the storage of oil and gas reservoirs. According to statistics, the total number of the oil-gas fields with the gypsum-rock as the cover layer is only 8%, but 55% of oil-gas reserves are controlled. The deep hanwu system is one of the most important sedimentary horizons of the Migao-salt rock in the world (Zhao-Menjun et al, 2017), and the potential of oil-gas exploration under the salt is huge. Taking the Tarim basin as an example, the ZS1 and ZS5 wells break through a dolomitic reservoir under salt, the existence of oil and gas under salt is proved, the LT1, TC1 and other wells drilled with Mitsubishi rock in the cold Wu system are not found with oil and gas under salt, and the poor cap sealing capability is the main cause of disfavor (Shiwei et al, 2019).
At present, scholars at home and abroad provide various methods and ideas for quantitatively evaluating the capping layer sealing capacity, start with the characteristic analysis of the capping layer from the macroscopic aspect and the microscopic aspect respectively, and mostly adopt a fuzzy evaluation method for evaluating the capping layer sealing capacity. For example, the microscopic and macroscopic evaluation results of the cold and armed system stratum in the region are researched in a quaternary manner and the like, the exploration condition of actual drilling is used as constraint, a fuzzy evaluation method is adopted, a comprehensive evaluation mode of the cap layer sealing capability is established, and the cap layer development energetic region is pointed out according to the evaluation results. The fuzzy mathematical method is rough in determining the weight coefficient and lacks certain accuracy; in addition, considering that the quantitative evaluation content has too many elements, the evaluation process is complicated, and the general applicability is poor.
Disclosure of Invention
Aiming at the problems of poor accuracy, low precision and the like in the prior art, the invention provides the quantitative evaluation method for the sealing capacity of the paste rock cover layer, which can accurately judge the sealing capacity of the paste rock cover layer and has the advantages of high precision, simplicity, practicability and wide application range.
In order to achieve the aim, the invention provides a quantitative evaluation method for the sealing capacity of a gypsum salt rock cover layer, which comprises the following specific steps:
selecting evaluation parameters: selecting lithology combination types, lithology partitions, dominant lithology accumulated thickness, cover layer accumulated thickness, maximum thickness of a thick single layer and a cover-to-ground ratio as evaluation parameters;
determining the weight: establishing a hierarchical structure model in AHP software by taking the closure capability of the cover layer as a decision target, taking lithology and thickness as intermediate elements and taking evaluation parameters as alternative schemes; analyzing the layer mechanism model through AHP software to generate a judgment matrix, comparing evaluation parameters pairwise through the judgment matrix, and obtaining the weight value of each evaluation parameter according to the judgment matrix scale or the input data of a sliding strip on the right side of an adjusting module in the AHP software;
evaluation parameter assignment step: describing and quantifying each evaluation parameter by adopting a fuzzy language to obtain each evaluation parameter assignment;
quantitative evaluation step: according to the weighted value and the assigned value of each evaluation parameter, a quantitative evaluation model is established by using a weighted average method, a comprehensive evaluation value C is calculated through the quantitative evaluation model, the sealing capacity of the gypsum rock cover layer is evaluated according to the comprehensive evaluation value C, and the quantitative evaluation model is expressed as follows:
C＝∑xi×yi (1)
in the formula, xiAs the i-th evaluation parameter, yiThe weight of the evaluation parameter of the ith item.
Preferably, in the evaluation parameter selection step, the lithology combination types are divided into three types of lithology combinations, namely a salt rock type, a plaster rock type and a limestone type according to the lithology proportion of a single well, the salt rock type comprises two types of lithology combinations of the salt rock type I and the salt rock type II, the plaster rock type comprises two types of lithology combinations of the plaster rock type I and the plaster rock type II, and the limestone type comprises two types of lithology combinations of the limestone rock type I and the limestone rock type II.
Preferably, the specific steps for dividing the lithology combination type are as follows: according to the relative contents of the gypsum rock and the salt rock, dividing the combination with the salt rock content higher than the gypsum rock into salt rock types, dividing the combination with the salt rock content more than or equal to 40 percent into salt rock type I, and dividing the combination with the salt rock content less than 40 percent into salt rock type II; the combination with the content of the gypsum rock higher than that of the salt rock is divided into a gypsum type I, the content of the gypsum rock and the mudstone is more than or equal to 40 percent, and the content of the gypsum rock and the mudstone is less than 40 percent, and the combination is divided into a gypsum type II; the limestone and mudstone content is more than or equal to 40 percent and is divided into a limestone I type, and the limestone and mudstone content is less than 40 percent and is divided into a limestone II type.
Preferably, in the evaluation parameter selection step, the determination method of the dominant lithology comprises the following steps: and screening the lithology with strong physical property sealing capability by taking the breakthrough pressure of 4MPa as a boundary, and determining the lithology with the breakthrough pressure of more than 4MPa as the dominant lithology.
Preferably, in the evaluation parameter selection step, the thick monolayer is a monolayer with a thickness of more than 10m in the dominant lithology.
Preferably, in the evaluation parameter assignment step, each evaluation parameter is described by using a fuzzy language and divided into five grades, amplitude intervals are (0,1], (1,2], (2,3], (3,4], (4, 5), and single evaluation parameter assignment is obtained by quantifying according to a single evaluation parameter value.
Compared with the prior art, the invention has the advantages and positive effects that:
(1) the quantitative evaluation method for the sealing capacity of the gypsum rock cover layer provided by the invention is based on a fuzzy teaching method, fully considers the characteristics of the cover layer in the macroscopic aspect and the microscopic aspect, introduces a microscopic factor-breakthrough pressure in the analysis process of the macroscopic factors such as lithology, thickness and the like, divides the lithology with the breakthrough pressure of more than 4MPa into the dominant lithology, divides the thickness in a dominant lithology section into thick single layers, and introduces an analytic hierarchy process to determine the weight of each factor in an evaluation system when the cover layer sealing capacity is controlled by multiple factors together, so that the influence of human subjective factors on the evaluation of the cover layer sealing capacity is reduced, and the accuracy and precision of the evaluation are improved.
(2) The quantitative evaluation method for the sealing capacity of the gypsum-rock cover layer provided by the invention is simple and easy to implement, has wide applicability, has the characteristics of accuracy, reliability and high efficiency, is convenient to popularize in oil field exploration, and has guiding reference significance for exploration of deep oil and gas reservoirs under salt.
Drawings
FIG. 1 is a flow chart of a quantitative evaluation method for sealing ability of a gypsum rock cover layer according to an embodiment of the invention;
FIG. 2 is a triangular plate for limestone lithology differentiation and evaluation according to an embodiment of the present invention;
FIG. 3 is a triangular plate for cloud lithology differentiation and evaluation according to an embodiment of the present invention;
FIG. 4 is a schematic diagram of the AHP software process and data input according to the present invention;
FIG. 5 is a schematic diagram illustrating the division of the lithologic combination types of the middle-lower Han dynasty gypsum rock type cap layer in the Tarim basin according to the embodiment of the present invention;
FIG. 6 is a schematic diagram of evaluation results of sealing capability of Tarim basin gypsum salt rock and oil gas display analysis according to an embodiment of the present invention.
Detailed Description
The invention is described in detail below by way of exemplary embodiments. It should be understood, however, that elements, structures and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.
Referring to fig. 1, the invention provides a quantitative evaluation method for sealing capability of a gypsum rock cover layer, which comprises the following specific steps:
s1, evaluation parameter selection: selecting lithology combination type, lithology partition, dominant lithology accumulated thickness, cover layer accumulated thickness, maximum thickness of a thick single layer and cover-to-ground ratio as evaluation parameters.
It should be noted that the analysis of the dominant lithology and the thick monolayer in the cover layer macro characteristics covers the cover layer micro characteristics-breakthrough pressure, so that 6 main influence factors of lithology combination type, lithology partition, dominant lithology accumulated thickness, cover layer accumulated thickness, thick monolayer maximum thickness and cover area ratio are selected as evaluation parameters in the evaluation system of the sealing capability of the gypsum rock cover layer in combination with the cover layer macro and micro characteristic analysis.
The lithology division is very important when the gypsum-rock cover layer of the Hanwu system is analyzed, the lithology combination type is divided into three types of lithology combinations of a salt rock type, a gypsum rock type and a limestone rock type according to the lithology proportion of a single well, the salt rock type comprises two types of lithology combinations of the salt rock type I and the salt rock type II, the gypsum rock type comprises two types of lithology combinations of the gypsum rock type I and the gypsum rock type II, and the limestone rock type comprises two types of lithology combinations of the limestone rock type I and the limestone rock type II. Specifically, the method is characterized in that the relative contents of the gypsum rock and the salt rock are distinguished, the combination with the salt rock content higher than the gypsum rock is divided into salt rock types, the salt rock content is larger than or equal to 40% and is divided into salt rock I types, and the salt rock content is smaller than 40% and is divided into salt rock II types. The combination with the content of the gypsum rock higher than that of the salt rock is divided into a gypsum type, the content of the gypsum rock and the mudstone in the gypsum type is more than or equal to 40 percent and is divided into a gypsum type I, and the content of the gypsum rock and the mudstone is less than 40 percent and is divided into a gypsum type II. In addition to the common lithology of the cap rock formed by the gypsum rock, the salt rock, the mudstone and the like, the limestone can also become a part for researching the cap rock because the displacement pressure of the limestone is greater than that of the dolomite, the limestone and mudstone content which is more than or equal to 40 percent is divided into a limestone I type, and the limestone and mudstone content which is less than 40 percent is divided into a limestone II type.
And (4) considering that the physical properties of various rock types in the limestone and dolomite have large differences, and performing lithological partition evaluation. Specifically, only marbled limestone (breakthrough pressure 7.69MPa) and claystone (breakthrough pressure 8.28MPa) in the limestone are superior lithology, while the lithology such as granular limestone is less than 4MPa, and is not the superior lithology of the composition cover layer, and is divided into other limestone, which is distinguished from marbled limestone and claystone, and the three units in the triangular plate are evaluated in a partition mode by taking the marbled limestone, the marbled limestone and other limestone as the lithology of the limestone, and are divided into five areas a-E, and the lithology of the areas a-E gradually becomes worse (see fig. 2). Similarly, the margarite cloud rock and the clayey cloud rock with the average breakthrough pressure of more than 4MPa in the cloud rock are distinguished from other cloud rocks, the clayey cloud rock and other cloud rocks are used as three units in the cloud rock lithology zone evaluation triangular plate and are divided into five areas A-E, and the lithology of the areas A-E gradually becomes worse (see figure 3).
Specifically, the determination method of the dominant lithology is as follows: and screening the lithology with strong physical property sealing capability by taking the breakthrough pressure of 4MPa as a boundary, and determining the lithology with the breakthrough pressure of more than 4MPa as the dominant lithology.
A thick monolayer is a monolayer with a thickness greater than 10m in the dominant lithology. Specifically, in the process of analyzing the thickness of a single layer, the physical property sealing capacity is considered, the dominant lithology with the breakthrough pressure of more than 4MPa is screened, and the single layer with the thickness of more than 10m in the dominant lithology is determined as the thick single layer.
S2, weight determination: the method comprises the steps of taking the closure capacity of the cover layer as a decision target, taking the lithology and the thickness as intermediate elements, taking evaluation parameters of lithology combination type, lithology partition, dominant lithology accumulated thickness, cover layer accumulated thickness, maximum thickness of a thick single layer and cover ground as alternative schemes, and establishing a hierarchical structure model in AHP software (see figure 4). Analyzing the layer mechanism model through AHP software to generate a judgment matrix, comparing evaluation parameters pairwise through the judgment matrix, and obtaining each evaluation parameter weight value (see table 2) according to judgment matrix scale (the meaning of the judgment matrix scale is shown in table 1, and scale data is shown in fig. 4) or adjustment module right side sliding strip input data in the AHP software.
TABLE 1
| Scale | Means of |
| (7,9] | Indicating that Fi is absolutely important compared to Fj |
| (5，7] | Indicating that Fi is important compared to Fj |
| (3，5] | Indicating that Fi is more important than Fj |
| (1，3] | Indicating that Fi is somewhat important compared to |
| 1 | Indicating that factors Fi and Fj are equally important when compared to Fj |
| [1/3，1) | Indicating that factors Fi compares to Fj, Fj being of slight importance |
| [1/5，1/3) | Indicating that factors Fi compares with Fj, which is important |
| [1/7，1/5) | Indicating that factors Fi compares with Fj, Fj being important |
| [1/9，1/7) | Indicating that factors Fi compares with Fj, Fj being absolutely important |
TABLE 2
S3, evaluation parameter assignment step: and describing and quantifying each evaluation parameter by adopting a fuzzy language to obtain each evaluation parameter assignment.
And describing each evaluation parameter by adopting a fuzzy language, dividing the evaluation parameter into five grades, wherein amplitude intervals are respectively (0,1], (1,2], (2,3], (3, 4) and (4, 5), quantifying according to the numerical value of the single evaluation parameter to obtain the assignment of the single evaluation parameter, and referring to a table 3 for each evaluation parameter assignment condition.
TABLE 3
S4, quantitative evaluation step: according to the weighted value and the assigned value of each evaluation parameter, a quantitative evaluation model is established by using a weighted average method, a comprehensive evaluation value C is calculated through the quantitative evaluation model, the sealing capacity of the gypsum rock cover layer is evaluated according to the comprehensive evaluation value C, and the quantitative evaluation model is expressed as follows:
C＝∑xi×yi (1)
in the formula, xiAs the i-th evaluation parameter, yiThe weight of the evaluation parameter of the ith item.
The larger the comprehensive evaluation value C is, the stronger the sealing capacity of the gypsum rock cover layer is, the more favorable the storage of deep oil and gas reservoirs under salt is, and the smaller the risk of oil and gas drilling is; on the contrary, the weaker the sealing capability of the gypsum-rock cover layer is, the less favorable the storage of deep oil-gas reservoirs under salt is, and the greater the risk of oil-gas drilling is. When the comprehensive evaluation value C of the cover layer is 3-4, the quality of the cover layer is good; when the comprehensive evaluation value C of the cover layer is 2-3, the quality of the cover layer is general; when the cap layer comprehensive evaluation value C is 1 to 2, the cap layer quality is poor.
It should be noted that the sequence of step S2 and step S3 may be interchanged, or may be performed simultaneously.
The quantitative evaluation method for the sealing capacity of the shale rock cover layer is based on a fuzzy mathematical method, fully considers the characteristics of the cover layer in the macroscopic and microscopic aspects, introduces a microscopic factor-breakthrough pressure in the analysis process of the macroscopic factors such as lithology, thickness and the like, divides the lithology with the breakthrough pressure of more than 4MPa into the dominant lithology, and divides the lithology with the dominant lithology into thick single layers with the thickness of more than 10m in the dominant lithology section. When the capping layer sealing capacity is controlled by multiple factors together, an analytic hierarchy process (AHP for short) is introduced to determine the weight of each factor in an evaluation system, so that the influence of human subjective factors on evaluation is reduced, an evaluation standard of the capping layer sealing capacity of the gypsum rock is formulated, the capping layer sealing capacity of the deep oil and gas reservoir can be accurately judged, and the application range is wide.
In order to describe the quantitative evaluation method of blocking capability of the gypsum rock type cover coat in more detail, the method of the present invention is further described below with reference to specific examples.
Example (b):
the Tarim basin is located in the south of the Uygur autonomous region in Xinjiang and is the largest inland oily-gas basin in China. The reservoir is a hydrocarbon source rock of Yuertusi group of Hanwu system, a Shoebulake dolomite reservoir and a cover layer of Wusonger group-avata group, and a deep and high-quality raw storage cover combination under the salt in the research area is formed. Large-area pasty salt rock strata are developed in a platform basin area of a Tarim basin by the Hanwu system, and the Ordok system on salt finds a billion-ton-grade large oil-gas field derived from hydrocarbon source rock under salt; with the breakthrough of ZS1, ZS5 wells in dolomitic reservoirs under salt, the presence of hydrocarbons under salt has been confirmed. Meanwhile, the oil gas is not found in the salt in the LT1, TC1 and other wells drilled with the Mitsui rock in the cold and military systems, which shows that the oil gas distribution difference under the control of the covering layer sealing capability is large. Therefore, the Tarim basin Han Wu system gypsum rock is selected as a research horizon, and the cover layer sealing capacity of the Tarim basin Han Wu system gypsum rock is evaluated by the quantitative evaluation method. The specific process is as follows:
and (3) selecting 14 wells in the research area, which reveal the formation of the Han-dynasty, and dividing the rock combination types through seismic data, logging and the like (see fig. 5). Statistics of individual well lithology classification, data in table 4, triangular chart for evaluation of input lithology zone (fig. 2, fig. 3)
TABLE 4
The single evaluation parameter data is evaluated by using an evaluation parameter evaluation table (namely table 3) according to a single evaluation parameter value or a partition, and is substituted into the formula (1) for calculation, and the data, the evaluation value and the calculation result are shown in table 5.
TABLE 5
As can be seen from the evaluation results in Table 5, the capping ability value C of the gypsum salt rock of the Hanwu system in the Baschu region is between 2.49 and 4.17, the average value is 3.54, and the quality of the capping layer is good; the sealing capacity value C of the gypsum salt rock cover layer of the area of the tower in the cold and armed systems is 1.5-2.6, the average value is 2.07, and the whole sealing capacity is in a grade from normal to bad; the sealing capacity values C of the talbe uplifting cold-armed system gypsum salt rock cover layers are all less than 2, and the talbe uplifting cold-armed system gypsum salt rock cover layers belong to poor cover layers.
It should be noted that, in order to clarify the control effect of the self-sealing ability of the cover layer on the deep oil gas distribution, the report of the single-well comprehensive histogram, the completion geological summary and the like is combined, the oil gas display layer section and the thickness of the single well are counted, the relative positions of the development horizon of the gypsum rock of the Hanwu system and the oil gas display horizon are divided into three types, namely, the salt-below type, the salt-below main type and the salt-above main type. Because the reservoir conditions of oil and gas under salt are complex and may be influenced by factors such as oil and gas sources, transportation conditions and the like, the oil and gas display is not performed on the wells such as 1,2, Job probe 1 and the like, so that only the well with the oil and gas display is selected for comparative analysis when the sealing capacity of the gypsum-rock cover layer and the oil and gas display relation are analyzed.
The evaluation result has a certain positive correlation with the deep oil gas display of the Tarim basin in the current research area, namely the self sealing capacity of the gypsum rock cover layer has a certain control effect on the oil gas display. Referring to FIG. 6, C values > 2, i.e., generally good quality cap layers, are mostly only under-salt or under-salt oil gas, while C values < 2, cap layer quality is poor and oil gas is shown as over-salt.
The above-described embodiments are intended to illustrate rather than to limit the invention, and any modifications and variations of the present invention are possible within the spirit and scope of the claims.
Claims (6)
1. A quantitative evaluation method for sealing capability of a gypsum rock cover layer is characterized by comprising the following specific steps:
selecting evaluation parameters: selecting lithology combination types, lithology partitions, dominant lithology accumulated thickness, cover layer accumulated thickness, maximum thickness of a thick single layer and a cover-to-ground ratio as evaluation parameters;
determining the weight: establishing a hierarchical structure model in AHP software by taking the closure capability of the cover layer as a decision target, taking lithology and thickness as intermediate elements and taking evaluation parameters as alternative schemes; analyzing the layer mechanism model through AHP software to generate a judgment matrix, comparing evaluation parameters pairwise through the judgment matrix, and obtaining the weight value of each evaluation parameter according to the judgment matrix scale or the input data of a sliding strip on the right side of an adjusting module in the AHP software;
evaluation parameter assignment step: describing and quantifying each evaluation parameter by adopting a fuzzy language to obtain each evaluation parameter assignment;
quantitative evaluation step: according to the weighted value and the assigned value of each evaluation parameter, a quantitative evaluation model is established by using a weighted average method, a comprehensive evaluation value C is calculated through the quantitative evaluation model, the sealing capacity of the gypsum rock cover layer is evaluated according to the comprehensive evaluation value C, and the quantitative evaluation model is expressed as follows:
C＝∑xi×yi (1)
in the formula, xiAs the i-th evaluation parameter, yiThe weight of the evaluation parameter of the ith item.
2. The method for quantitatively evaluating the sealing capability of the soft cover rock of claim 1, wherein in the evaluation parameter selection step, the lithologic combination types are divided into three types of lithologic combinations of a salt rock type, a soft rock type and a limestone type according to the lithologic proportion of a single well, the salt rock type comprises two types of lithologic combinations of the salt rock type I and the soft rock type II, the soft rock type comprises two types of lithologic combinations of the soft rock type I and the soft rock type II, and the limestone type comprises two types of lithologic combinations of the limestone type I and the soft rock type II.
3. The quantitative evaluation method for the sealing capability of the gypsum rock cover layer as claimed in claim 2, wherein the specific steps for dividing the lithologic combination type are as follows: according to the relative contents of the gypsum rock and the salt rock, dividing the combination with the salt rock content higher than the gypsum rock into salt rock types, dividing the combination with the salt rock content more than or equal to 40 percent into salt rock type I, and dividing the combination with the salt rock content less than 40 percent into salt rock type II; the combination with the content of the gypsum rock higher than that of the salt rock is divided into a gypsum type I, the content of the gypsum rock and the mudstone is more than or equal to 40 percent, and the content of the gypsum rock and the mudstone is less than 40 percent, and the combination is divided into a gypsum type II; the limestone and mudstone content is more than or equal to 40 percent and is divided into a limestone I type, and the limestone and mudstone content is less than 40 percent and is divided into a limestone II type.
4. The quantitative evaluation method of the sealing capability of the gypsum rock cover layer as claimed in claim 1, wherein in the evaluation parameter selection step, the determination method of the dominant lithology is as follows: and screening the lithology with strong physical property sealing capability by taking the breakthrough pressure of 4MPa as a boundary, and determining the lithology with the breakthrough pressure of more than 4MPa as the dominant lithology.
5. The quantitative evaluation method of blocking ability of a Mirabilite cap layer according to claim 4, wherein in the evaluation parameter selection step, the thick single layer is a single layer with a thickness of more than 10m in the dominant lithology.
6. The quantitative evaluation method for the sealing capacity of the soft rock cover layer according to claim 1, wherein in the evaluation parameter assignment step, fuzzy language is adopted to describe each evaluation parameter, the evaluation parameter is divided into five grades, the amplitude intervals are (0,1], (1,2], (2,3], (3,4], (4, 5), and the single evaluation parameter assignment is obtained through quantification according to the single evaluation parameter value.
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