A method for identifying volcanic rocks and sedimentary rocks based on well logging curves

Abstract

The invention discloses a method for identifying volcanic rocks and sedimentary rocks based on logging curves, comprising: selecting key parameters of a study area; establishing a dual-parameter sensitivity curve relationship chart of the volcanic rocks and sedimentary rocks in the study area by using the key parameters to determine the boundary mathematical relationship between the volcanic rocks and sedimentary rocks; determining a standard comparison constant and a fixed point by using the boundary mathematical relationship, establishing a straight line equation between the fixed point and an unknown lithology point in the study area to obtain a comparison constant, and identifying the lithology of sedimentary rocks and volcanic rocks at the unknown lithology point according to the positional relationship between the comparison constant and the standard comparison constant; the method solves the problems of being unable to quantitatively identify, unsatisfactory identification reliability and low identification efficiency in the existing multi-parameter chart method for identifying the lithology of volcanic rocks and sedimentary rocks in volcanic fault basins.

Description

Technical Field

[0001] The invention relates to a method for lithology identification in the field of oil and gas exploration, and in particular to a method for identifying sedimentary rocks and volcanic rocks in a volcanic fault basin. Background Art

[0002] The lithology type of rocks records a large amount of original geological information. Accurate identification of lithology is of great geological significance for in-depth understanding of the structure and sedimentary environment.

[0003] Volcanic fault basins often experience the dual effects of "water and fire", forming complex lithologies, making it difficult to accurately distinguish between sedimentary rocks and volcanic rocks. The degree of development of sedimentary rocks determines the resource potential of volcanic fault basins, and the development of volcanic rocks provides storage space for oil and gas accumulation. Therefore, accurately identifying sedimentary rocks and volcanic rocks in volcanic fault basins is of great significance to understanding the exploration potential of basins.

[0004] Generally, the data for identifying sedimentary rocks and volcanic rocks come from two main sources: the first is laboratory analysis of rock core slices, and the second is comprehensive identification from conventional logging data, specifically by establishing electrical intersection identification plates for different lithologies to determine lithology.

[0005] The application of coring data for laboratory analysis of ordinary thin sections or cast thin sections is to determine the lithology by describing the parameters such as the terrigenous debris content, filling materials, debris structure characteristics, pore type, structural structure, mineral composition and characteristics of the rock sample under a microscope. It has high accuracy, but is limited by drilling and coring. It can only determine the lithology of the coring section, but cannot understand the lithology distribution of the entire well.

[0006] The multi-parameter plate method is currently a more effective means of using conventional logging data to comprehensively identify the lithology distribution in the well. This method uses the response characteristics of logging data to different lithologies to determine the distribution of lithologies in the well, and establishes relevant plates by optimizing multiple characteristic parameters to determine the type of unknown lithology. This method has better solved the problem of lack of samples, especially when combined with special logging data such as imaging logging, it can more accurately identify unknown lithologies.

[0007] Specifically, the use of multi-parameter plate method to identify sedimentary rocks and volcanic rocks requires projecting the data of all known points in each area into a rectangular coordinate system, and artificially drawing the lithology boundary between volcanic rocks and sedimentary rocks. In the plate method, the lithology boundary is parallel to the Y axis and then parallel to the X axis, forming an L-shaped or reverse L-shaped line. Figure 1In the figure, after the L-shaped boundary is fixed, the area to the right and above the L-shaped boundary is volcanic rock, and the area to the left and below the L-shaped boundary is sedimentary rock. The hollow point indicates that if you want to determine the lithology of the unknown point, you need to project the data of the point onto the plate. If it is projected into the volcanic rock area, the lithology of the point is considered to be volcanic rock. If it is projected into the sedimentary rock area, the lithology of the point is considered to be sedimentary rock.

[0008] The defects of the existing multi-parameter plate method are: 1) It can only be identified qualitatively, not quantitatively, and there are many human factors; 2) It is limited by special logging data (such as in areas without special logging data), and the recognition reliability of the multi-parameter plate method is not ideal; 3) The recognition process is cumbersome and the recognition efficiency is low.

[0009] The reasons for the above defects are: 1. The boundary between the two lithologies in the multi-parameter plate method is uncertain, and it is impossible to find a mathematical equation to express it in the rectangular coordinate system, that is, it cannot be quantitatively described by means of formulas. Since the boundary of lithology discrimination is drawn manually, different people will draw different positions based on their subjective understanding, so the human factor is relatively large in the multi-parameter plate method. 2. In the multi-parameter plate method, after the L-shaped or reverse L-shaped lithology boundary of a certain area is fixed, every time there is a new unknown point, the data of the point must be re-projected onto the plate to see whether the point is on the left or right side of the lithology boundary, above or below, in order to know the lithology of the point. Therefore, the lithology identification process of the multi-parameter plate method is very cumbersome, inefficient and slow in practical application. 3. In many areas, there is often less special well data, and only a few wells have data, which makes it difficult to promote and the scope of application is limited. Summary of the invention

[0010] In view of this, the present invention provides a method for identifying volcanic rocks and sedimentary rocks based on logging curves, which solves the problems of the existing multi-parameter plate method for lithology identification of volcanic rocks and sedimentary rocks in volcanic fault basins, such as the inability to quantitatively identify, unsatisfactory identification reliability and low identification efficiency.

[0011] To achieve the above-mentioned purpose of the invention, the method for identifying volcanic rocks and sedimentary rocks based on well logging curves comprises:

[0012] Select key parameters of the study area;

[0013] Using the key parameters, a dual-parameter sensitivity curve relationship chart of the volcanic rock and sedimentary rock in the study area is established to determine the boundary mathematical relationship between the volcanic rock and the sedimentary rock;

[0014] The boundary mathematical relationship is used to determine the standard comparison constant and the fixed point, and a straight line equation is established between the fixed point and the unknown lithology point in the study area to obtain the comparison constant. The lithology of sedimentary rock and volcanic rock of the unknown lithology point is identified according to the positional relationship between the comparison constant and the standard comparison constant.

[0015] Furthermore, the method for establishing the dual-parameter sensitivity curve relationship diagram includes:

[0016] Combining the selected key parameters in pairs and projecting the volcanic rock and sedimentary rock data to establish a dual-parameter combination intersection chart;

[0017] Among the dual-parameter combination intersection graphs, the graph that can most clearly distinguish the volcanic rock from the sedimentary rock is selected as the dual-parameter sensitivity curve relationship graph.

[0018] Furthermore, the method for determining the boundary mathematical relationship between volcanic rock and sedimentary rock comprises:

[0019] Using the graphical method, the lithological boundary between volcanic rock and sedimentary rock is established on the dual-parameter sensitivity curve relationship chart;

[0020] The lithological boundary is used to establish the boundary mathematical relationship between volcanic rock and sedimentary rock.

[0021] Furthermore, the lithology boundary is a boundary that can distinguish volcanic rock and sedimentary rock data above a first set value.

[0022] Further, the boundary mathematical relationship corresponds to the lithology boundary straight line equation;

[0023] The equation of the lithology boundary line, its slope is used as the standard contrast constant, and its intersection with the x-axis is used as the fixed point.

[0024] Further, the contrast constant is the slope of the straight line equation;

[0025] and / or,

[0026] The first set value is 95%.

[0027] Further, a lithology identification curve is established using the fixed points and all depth points of the single well in the study area;

[0028] The lithology identification curve and the lithology boundary line are superimposed, and the lithology of volcanic rock and sedimentary rock is identified at a certain depth point of the single well by using the positional relationship between the lithology identification curve and the lithology boundary line.

[0029] Furthermore, the method for establishing the lithology identification curve includes:

[0030] The slope of the straight line between the fixed point and each of the depth points is fitted to obtain the lithology identification curve.

[0031] Furthermore, the method for selecting the key parameters includes:

[0032] Determine the logging parameters of sedimentary and volcanic rocks based on the laboratory rock type identification and analysis results;

[0033] The R cluster analysis method is used to perform sensitivity analysis on the logging parameters of sedimentary rocks and volcanic rocks to determine the key parameters.

[0034] Furthermore, the logging curve includes:

[0035] Natural gamma GR, compensated neutron porosity CNL, density DEN, resistivity LLD and acoustic time difference AC.

[0036] The present invention has the following beneficial effects:

[0037] The method of the present invention first selects key parameters that are sensitive to lithology discrimination in the study area, then uses the key parameters to select key parameter combinations of sedimentary rocks and volcanic rocks in the study area, and establishes a boundary mathematical relationship between volcanic rocks and sedimentary rocks according to a dual-parameter sensitivity curve relationship chart corresponding to the key parameter combination, because the boundary mathematical relationship can clearly divide the lithology boundary of volcanic rocks and sedimentary rocks at a certain point in the study area, thereby reducing personal subjective errors and achieving the purpose of quantitative description; in addition, the positional relationship between the unknown lithology point and the lithology dividing line corresponding to the boundary mathematical relationship can be used to identify the volcanic rocks and sedimentary rocks at the point, so the reliability and convenience of lithology identification in the disclosed method are greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0039] Figure 1 It is a schematic diagram of lithology identification using a multi-parameter plate method, which is the background technology of the present invention;

[0040] Figure 2 This is a flow chart of a method for identifying volcanic rocks and sedimentary rocks based on well logging curves according to Embodiment 1 of the present invention;

[0041] Figure 3 It is a mathematical relationship version of the boundary between volcanic rock and sedimentary rock in the first embodiment of the present invention;

[0042] Figure 4 This is a lithology identification column chart of Well X6 in the Hongqi Sag according to the second embodiment of the present invention. DETAILED DESCRIPTION

[0043] The present invention is described below based on embodiment, but it is worth noting that the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. However, for the part not described in detail, those skilled in the art can also fully understand the present invention.

[0044] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present invention, and the drawings are not actually drawn to scale.

[0045] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0046] The Jurassic system in the Hongqi Depression of the Hailar Basin (hereinafter referred to as the study area) has interbedded sedimentary rocks and volcanic rocks with complex and diverse lithologies. In the embodiments of the present disclosure, the identification of volcanic rocks and sedimentary rocks in the study area is taken as an example to describe in detail the specific technical scheme used to implement the method of the present disclosure.

[0047] Embodiment 1

[0048] Figure 2 is a flow chart of a method for identifying volcanic rocks and sedimentary rocks based on well logging curves according to an embodiment of the present invention; Figure 2 As shown: the method for identifying volcanic rocks and sedimentary rocks based on logging curves includes: step S101: selecting key parameters of the study area; step S102: using the key parameters to establish a dual-parameter sensitivity curve relationship chart of volcanic rocks and sedimentary rocks in the study area to determine the boundary mathematical relationship between volcanic rocks and sedimentary rocks; step S103: using the boundary mathematical relationship to determine standard comparison constants and fixed points, establishing a straight line equation between the fixed points and the unknown lithology points in the study area to obtain comparison constants, and identifying the lithology of sedimentary rocks and volcanic rocks at the unknown lithology points according to the positional relationship between the comparison constants and the standard comparison constants.

[0049] Step S101: Select key parameters of the study area. The specific selection method is as follows:

[0050] (1) Performing conventional standard processing on the well logging curves in the study area. The embodiments of the present disclosure and possible embodiments use core tracing and acoustic histogram methods to calibrate and standardize the actual well logging data in the study area; obtaining laboratory rock type identification and analysis results in the study area.

[0051] (2) The embodiments and possible embodiments of the present disclosure determine the logging parameters of sedimentary rocks and volcanic rocks based on the results of laboratory rock type identification and analysis. For example, the volcanic rocks in the Hongqi Depression show natural gamma GR 40.6-76.5 API, compensated neutron porosity CNL 5.0-20.1%, density DEN 2.40-2.71 g / cm3, resistivity LLD 33.9-182.5 Ω·m, and acoustic time difference AC 50.8-75.4 μs / ft on the logging curve; the sedimentary rocks show natural gamma GR 120.6-276.5 API, compensated neutron porosity CNL 10.0-40.1%, density DEN 2.20-2.71 g / cm3, resistivity LLD 13.9-92.5 Ω·m, and acoustic time difference AC 70.8-112.4 μs / ft on the logging curve.

[0052] (3) The embodiments of the present disclosure and possible embodiments use the R cluster analysis method to perform a sensitivity analysis on the logging parameters of the above-mentioned sedimentary rocks and volcanic rocks to lithology discrimination, and determine the key parameters of the two rock types of sedimentary rocks and volcanic rocks; in the embodiments of the present disclosure, natural gamma ray GR, compensated neutron porosity CNL and acoustic wave time difference AC can meet the above conditions and can be used as key parameters.

[0053] Step S102: using the key parameters to establish a dual-parameter sensitivity curve relationship chart of the volcanic rock and sedimentary rock in the study area to determine the boundary mathematical relationship between the volcanic rock and the sedimentary rock. The specific determination method is as follows:

[0054] (1) The three key parameters of the natural gamma ray GR curve, the compensated neutron porosity CNL curve and the acoustic time difference AC curve obtained in step S101 are combined in pairs, and the volcanic rock and sedimentary rock data are projected onto different dual-parameter combination intersection charts. It can be intuitively seen that the volcanic rock and sedimentary rock can be clearly distinguished through the GNL-GR combination intersection chart. Therefore, the key parameter combination with the best effect for identifying sedimentary rocks and volcanic rocks in this study area is the natural gamma ray GR and the compensated neutron porosity CNL. The GNL-GR combination intersection chart is used as the dual-parameter sensitivity curve relationship chart of the embodiment of the present disclosure.

[0055] (2) Using the CNL curve data as the abscissa x and the GR curve data as the ordinate y, all known volcanic and sedimentary rock data are projected onto the GNL-GR combined intersection chart. The lithologic boundary between volcanic and sedimentary rocks can be obtained by applying the graphical method. The lithologic boundary requires that the volcanic and sedimentary rock data that meet the set value can be distinguished on both sides of the boundary. The lithologic boundary can be used to determine the mathematical relationship between the boundaries of volcanic and sedimentary rocks (such as Figure 3 The setting value used in the embodiment of the present disclosure is 95%, and other values ​​may also be used.

[0056] Step S103: Determine the standard contrast constant and the fixed point by using the boundary mathematical relationship, establish a straight line equation between the fixed point and the unknown lithology point in the study area to obtain the contrast constant, and perform lithology identification of sedimentary rock and volcanic rock on the unknown lithology point according to the positional relationship between the contrast constant and the standard contrast constant. The identification method is as follows:

[0057] (1) In the GNL-GR combined intersection diagram, the mathematical relationship between the volcanic rock and the sedimentary rock boundary of the embodiment of the present disclosure is linear, that is, the equation of the lithological boundary line between the sedimentary rock and the volcanic rock is y=kx+b (k<0), and the slope k of the equation is used as the standard comparison constant; the coordinates of the intersection point M of the equation of the lithological boundary line between the sedimentary rock and the volcanic rock and the x-axis are set to (x, 0).

[0058] like Figure 3 As shown in Table 1, the straight line equation for the lithologic boundary between sedimentary rock and volcanic rock established in the embodiment of the present disclosure is: y=-6.5435x+253.742, k=-6.5435, and the coordinates of the intersection point M of the straight line equation for the lithologic boundary and the x-axis are (38.78, 0).

[0059] Table 1 Equation of the straight line between sedimentary and volcanic rocks

[0060] Lithology Identification Application Slope value Equation of limit line Fixed point M Used to distinguish sedimentary from volcanic rocks k=-6.5435 y=-6.5435x+253.742 (38.78,0)

[0061] (2) In the embodiment of the present disclosure, point M (38.78, 0) is used as a fixed point, and a straight line equation is established through the unknown lithology point α (xi, yi) through point M, that is, y = kix + bi (e.g. Figure 3 as shown).

[0062] (3) Use the positional relationship between ki and k to determine whether the lithology corresponding to a certain depth point (i.e., unknown lithology point) of the single well is sedimentary rock or volcanic rock; Figure 3 As shown, in the embodiment of the present disclosure, when ki<k, the unknown point α is located in the sedimentary rock area above the straight line, and it can be judged as sedimentary rock. When ki>k, the unknown point α is located in the volcanic rock area below the straight line, and it can be judged as volcanic rock.

[0063] Embodiment 2

[0064] The method for determining the boundary mathematical relationship and fixed points of the volcanic rock and the sedimentary rock in the second embodiment is the same as that in the first embodiment. The difference is that the second embodiment of the present disclosure uses the fixed points and all the depth points of the single well in the study area to establish a lithology identification curve, superimposes the lithology identification curve and the lithology boundary line corresponding to the boundary mathematical relationship, and uses the positional relationship between the lithology identification curve and the lithology boundary line to identify the lithology of the volcanic rock and the sedimentary rock at a certain depth point of the single well; the specific identification method is as follows:

[0065] (1) Based on the convenience of application and digitalization, the natural gamma GR curve A and the compensated neutron porosity CNL curve B are used. All depth points of a single well have corresponding values ​​Ai and Bi on these two curves. The α (Bi, Ai) corresponding to each depth point and the fixed point M can form a series of straight lines with a slope of ki. They are fitted together into a new series of lithology identification curves composed of ki.

[0066] (2) In the embodiment of the present disclosure, the Kaben geological software is used to import the newly fitted lithology identification curve composed of ki and the straight line with the slope k of the lithology boundary straight line equation, and let them overlap and distinguish. The relationship between a certain point ki and k on the lithology identification curve is used to judge whether the lithology corresponding to a certain depth point of the single well is sedimentary rock or volcanic rock (such as Figure 4 as shown).

[0067] (3) When the ki corresponding to a certain depth point of a single well is at the end with a smaller k value, that is, the ki corresponding to the depth point in the figure is on the left side of the k straight line, it is identified as sedimentary rock; when the ki corresponding to a certain depth point is at the end with a larger k value, that is, the ki corresponding to the depth point in the figure is on the right side of the k straight line, it is identified as volcanic rock (such as Figure 4 as shown).

[0068] In the embodiments of the present disclosure, the method disclosed herein is used in the Hongqi Depression of the Hailar Basin to reduce the difficulty of identifying sedimentary rocks and volcanic rocks, and the accuracy of lithology identification can reach more than 90%. Combined with the Kaben software, the lithology can be further quickly and intuitively identified.

[0069] Therefore, the method for quickly identifying sedimentary rocks and volcanic rocks using logging curves in the embodiments of the present disclosure can quantitatively identify lithology, thereby reducing personal subjective errors, so the reliability of lithology identification of sedimentary rocks and volcanic rocks is relatively high; and the corresponding lithology identification can be performed through simple position relationship judgment, so the convenience and speed of lithology identification are greatly improved, it is not limited by special well data, improves efficiency, saves costs, and has certain promotion and application value and prospects.

[0070] In addition, the disclosed method can also be used to identify acidic volcanic rocks and intermediate-basic volcanic rocks. For example, it has been applied to multiple wells such as X2 Well and X5 Well in the Hongqi Sag, and the accuracy of identifying unknown lithology can reach more than 90%, achieving good results. In addition, the disclosed method can also be applied to stratigraphic division and comparison and reservoir prediction.

[0071] The above-mentioned embodiments are only embodiments of the present invention, and the description is relatively specific, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for those skilled in the art, without departing from the concept of the present invention, several modifications, equivalent substitutions, improvements, etc. can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be based on the attached claims.

Claims

1. A method for identifying volcanic rocks and sedimentary rocks based on well logging curves, characterized in that: include: Selecting key parameters of the study area, wherein the key parameters are natural gamma ray GR and compensated neutron porosity CNL; Using the key parameters to establish a dual-parameter sensitivity curve relationship chart of volcanic rocks and sedimentary rocks in the study area, using a graphical method to establish a lithological boundary line between volcanic rocks and sedimentary rocks on the dual-parameter sensitivity curve relationship chart, and using the lithological boundary line to establish a boundary mathematical relationship between volcanic rocks and sedimentary rocks; The standard contrast constant and the fixed point are determined by using the boundary mathematical relationship, and the determination method is: the boundary mathematical relationship corresponds to the lithology boundary straight line equation; the lithology boundary straight line equation, its slope k is used as the standard contrast constant, and its intersection with the x-axis is used as the fixed point; Establishing a straight line equation between the fixed point and the unknown lithology point in the study area to obtain a contrast constant, wherein the contrast constant is the slope of the straight line equation; According to the positional relationship between the comparison constant and the standard comparison constant, the lithology of sedimentary rock and volcanic rock of the unknown lithology point is identified, and the identification method is: Establishing a lithology identification curve using the fixed point and all depth points of the single well in the study area; superimposing the lithology identification curve and the lithology boundary line, and using the positional relationship between the lithology identification curve and the lithology boundary line to identify the lithology of volcanic rocks and sedimentary rocks at a certain depth point of the single well; The method for establishing the lithology identification curve comprises: Fitting the slope of the straight line between the fixed point and each of the depth points to obtain the lithology identification curve; The relationship between ki and k at a certain point on the lithology identification curve is used to determine the lithology corresponding to a certain depth point of the single well. When the ki corresponding to a certain depth point of the single well is at the end with a smaller k value, it is identified as sedimentary rock; when the ki corresponding to a certain depth point is at the end with a larger k value, it is identified as volcanic rock.

2. The method for identifying volcanic rocks and sedimentary rocks based on well logging curves according to claim 1, characterized in that: The method for establishing the dual-parameter sensitivity curve relationship chart comprises: Combining the selected key parameters in pairs and projecting the volcanic rock and sedimentary rock data to establish a dual-parameter combination intersection chart; Among the dual-parameter combination intersection graphs, the graph that can most clearly distinguish the volcanic rock from the sedimentary rock is selected as the dual-parameter sensitivity curve relationship graph.

3. The method for identifying volcanic rocks and sedimentary rocks based on well logging curves according to claim 1, characterized in that: The lithology boundary is a boundary that can distinguish volcanic rock and sedimentary rock data above a first set value.

4. The method for identifying volcanic rocks and sedimentary rocks based on well logging curves according to claim 3, characterized in that: The first set value is 95%.

Images