Method for qualitatively identifying geological sweet spots of shale reservoir

Abstract

The invention relates to a method for qualitatively identifying geological sweet spots of a shale reservoir, and belongs to the technical field of oil and gas development. The method specifically comprises the following steps: selecting a standard well in a research area, and describing dessert characteristics through special logging data and test analysis data of geochemical logging in combination with formation testing, yield and rock core display; for coring wells with complete logging series in a research area, a sensitive curve cross plot is formed by combining special logging data, test analysis data, oil testing, yield and rock core display description with common scale conventional logging curves, and sweet spot conventional curve response characteristics are qualitatively described through the sensitive curve cross plot; and constructing a dessert factor, analyzing logging response characteristics to establish a dessert standard, selecting key coring wells with complete logging series in a research area for verification, and determining the goodness of fit of the method. The method solves the problem that shale reservoir dessert recognition is difficult, the whole method is high in operability, and the method has important scientific guiding significance in old well review, unconventional oil and gas resource exploration and the like.

Description

Technical Field

[0001] The invention relates to a method for qualitatively identifying geological sweet spots in shale reservoirs, and belongs to the technical field of oil and gas development. Background Art

[0002] Identifying oil and gas sweet spots is a crucial step in developing reservoir stimulation plans for oil and gas wells. In low-permeability, unconventional reservoirs with multiple layers, thick layers, or long horizontal well sections, the "sweet spots" that contribute significantly to well production often account for less than 30% due to the high heterogeneity and interlayer differences between wells. Therefore, stimulation measures are needed to improve the flow environment in these sweet spots and achieve high production in individual wells. Inaccurate identification of sweet spots significantly reduces the relevance and effectiveness of stimulation efforts.

[0003] Conventional methods for identifying geological sweet spots include drilling logging, completion logging, and mechanical production logging. Drilling logging is subject to significant wellbore interference and has a limited detection range of only a few meters. Due to the large number of characteristic parameters, completion logging suffers from multi-solution errors caused by nonlinearity, leading to significant deviations in the results. Mechanical production logging can verify the accuracy of interpretation results. However, production logging is subject to stringent conditions and requires the use of mechanical logging instruments. These are often constrained by conditions such as completion methods and wellbore integrity. For example, wells with casing deformation, choke devices under the production string, or segmented ball-dropping sleeves cannot be subjected to production logging. Furthermore, the test data obtained from production logging is only a point-in-time data point, which is easily affected by the test environment and cannot reflect the dynamic information of a continuous production period. Therefore, production logging data does not provide complete guidance. Conventional methods for identifying geological sweet spots are difficult to identify. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for qualitatively identifying geological sweet spots in shale reservoirs. In the absence of special logging data, the method can qualitatively identify shale sweet spots through conventional logging curve intersection and determine favorable shale reservoirs. This solves the problem of difficult identification of shale reservoir sweet spots and has important scientific guidance significance for the review of old wells and the exploration of unconventional oil and gas resources.

[0005] The technical solution adopted by the present invention is a method for qualitatively identifying geological sweet spots in shale reservoirs, specifically:

[0006] Step 1: Select a standard well in the study area and describe the sweet spot characteristics by analyzing special well logging data and geochemical logging data, combined with oil testing, production, and core drilling results.

[0007] Step 2: For several cored wells in the study area with complete logging series, we generate sensitivity curve crossplots based on special logging data, laboratory analysis data, oil test data, production rate, and core display descriptions combined with commonly scaled conventional logging curves. This crossplot is used to qualitatively describe the response characteristics of the conventional curves at the sweet spot.

[0008] Step 3: Construct the sweet spot factor and analyze the logging response characteristics to establish the sweet spot standard, where the sweet spot factor = movable porosity × movable saturation × brittle mineral content;

[0009] Step 4: Select several other key core wells with complete logging series in the study area to verify steps 1 to 3 to determine the consistency of the method.

[0010] Furthermore, the special logging data in step 1 include nuclear magnetic resonance, downhole imaging and lithologic scanning, and the laboratory analysis data include total organic carbon TOC, free hydrocarbon content S1, brittleness, porosity, saturation and maturity.

[0011] Furthermore, the sensitivity curve cross-plot in step 2 is an acoustic time difference AC-resistivity RT cross-plot.

[0012] Furthermore, in step 3, the brittle mineral content = brittleness index × total mineral content.

[0013] Furthermore, the sweet spot standards in step 3 are as follows: Class I sweet spot rules are as follows: natural gamma: 110-115 API, resistivity >12Ω·m, acoustic wave travel time 260-300μs / m, movable porosity >3%, movable oil saturation >40%, brittleness index >50%, mainly silty laminar felsic shale, oil production intensity >0.4t / (dm); Class II sweet spot rules are as follows: natural gamma: 115-120 API, resistivity 6-12Ω·m, acoustic wave travel time 300-320μs / m s / m, movable porosity 2-3%, movable oil saturation 30-40%, brittleness index 40-50%, mainly composed of clayey laminae and silt laminae felsic shale, with an oil production intensity of 0.2-0.4t / (dm); the rules of Class III sweet spots are as follows: natural gamma >120API, resistivity <6Ω·m, sonic time difference >320μs / m, movable porosity <2%, movable oil saturation <40%, brittleness index <40%, mainly composed of clayey shale with clayey laminae, and an oil production intensity <0.2t / (dm).

[0014] Furthermore, step 5 is to promote the application to a certain region to summarize the sweet spot response characteristics of the conventional curve and establish a conventional curve identification sweet spot chart.

[0015] The present invention discloses a method for qualitatively identifying geological sweet spots in shale reservoirs. This method, without the need for specialized logging data, can be used to identify shale sweet spots using conventional curve intersection. This method allows for rapid qualitative identification of shale sweet spots and the identification of favorable shale reservoirs. This method addresses the difficulty of identifying sweet spots in shale reservoirs. The method is highly operational and offers important scientific guidance for reviewing old wells and exploring unconventional oil and gas resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0017] Figure 1 The figure shows a sweet spot diagram for identifying special well logging curve intersection in an example of the present invention;

[0018] Figure 2 The figure shows a sweet spot diagram identified by intersection of conventional logging curves in an example of the present invention;

[0019] Figure 3 Shown is a diagram showing the relationship between the sweet spot factor and the oil production intensity in an example of the present invention;

[0020] Figure 4 Shown is a comprehensive interpretation result diagram of key wells in the study area in the example of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] In order to further understand the content of the present invention, this technical solution is further described below in conjunction with specific implementation methods.

[0023] Example 1:

[0024] like Figures 1 to 4 As shown, this embodiment provides a method for qualitatively identifying shale reservoir geological sweet spots, specifically:

[0025] Standard wells in the study area were selected, and the characteristics of the sweet spots were described by combining special logging data such as nuclear magnetic resonance, downhole imaging and lithologic scanning, and laboratory analysis data such as total organic carbon (TOC), free hydrocarbon content (S1), brittleness, porosity, saturation and maturity from geochemical logging, with oil testing, production and core indications. In this example, a lacustrine shale sample from the Qingshankou Formation in the southern Songliao Basin was used as an example to conduct a correlation analysis of five parameters: oil recovery intensity, movable porosity, resistivity (RT), acoustic transit time (AC) and movable oil saturation.

[0026] For eight cored wells in the study area with complete logging series, we used special logging data, laboratory analysis data, oil testing, production, and core display descriptions combined with commonly scaled conventional logging curves to select and intersect the sensitivity curves reflecting reservoir characteristics to form acoustic transit time (AC)-resistivity (RT) crossplots. This crossplot was used to qualitatively describe the response characteristics of the conventional curves in the sweet spot.

[0027] Mobile porosity and mobile oil saturation reflect matrix mobility, while brittle mineral content reflects matrix compressibility. Shale oil production capacity is primarily controlled by matrix mobility and matrix compressibility. The sweet spot factor is constructed using the product of these three factors: sweet spot factor = mobile porosity × mobile saturation × brittle mineral content; where brittle mineral content = brittleness index × total mineral content.

[0028] like Figure 3 As shown in the figure, the correlation between the sweet spot factor and the oil production intensity is y = 0.5763x + 0.0228, where y is the oil production intensity, x is the sweet spot factor, and the correlation coefficient between the sweet spot factor and the oil production intensity is R 2 =0.9007, reaching above 0.9, and the oil production intensity is greater than 0.4t / (dm) as the Class I sweet spot layer. The sweet spot standard is established by analyzing the logging response characteristics, and the sweet spot standard is divided into three categories, as shown in Table 1. The sweet spot standards are as follows: Class I sweet spot rules are as follows: natural gamma: 110-115API, resistivity>12Ω·m, sonic wave time difference 260-300μs / m, movable porosity>3%, movable oil saturation>40%, brittleness index>50%, mainly silty laminae felsic shale, and oil production intensity>0.4t / (dm). The characteristics of Type II sweet spots are as follows: natural gamma ray: 115-120 API, resistivity 6-12 Ω·m, acoustic transit time 300-320 μs / m, movable porosity 2-3%, movable oil saturation 30-40%, brittleness index 40-50%, predominantly felsic shale with argillaceous and silty laminae, and oil production intensity 0.2-0.4 t / (dm). The characteristics of Type III sweet spots are as follows: natural gamma ray > 120 API, resistivity < 6 Ω·m, acoustic transit time > 320 μs / m, movable porosity < 2%, movable oil saturation < 40%, brittleness index < 40%, predominantly clayey shale with argillaceous laminae, and oil production intensity < 0.2 t / (dm).

[0029] Table 1

[0030]

[0031] The remaining five core wells with complete logging series in the study area were selected to verify steps 1 and 2 to determine the consistency of the method. Figure 4 The remaining five wells shown fall within the sweet spot range and can be widely used.

[0032] This method was applied to 20 key wells to summarize the sweet spot response characteristics of the conventional curve and establish a conventional curve sweet spot identification chart.

[0033] The above-established method for qualitatively identifying shale reservoir geological sweet spots based on conventional curve intersections, thereby identifying favorable shale reservoirs, solves the problem of identifying favorable shale reservoirs. The entire method is highly operational and has important scientific guidance for the review of old wells and the exploration of unconventional oil and gas resources.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for qualitatively identifying geological sweet spots in shale reservoirs, characterized in that: Step 1: Select a standard well in the study area and describe the sweet spot characteristics by analyzing special well logging data and geochemical logging data, combined with oil testing, production, and core drilling results. Step 2: For several cored wells in the study area with complete logging series, we generate sensitivity curve crossplots based on special logging data, laboratory analysis data, oil test data, production rate, and core display descriptions combined with commonly scaled conventional logging curves. This crossplot is used to qualitatively describe the response characteristics of the conventional curves at the sweet spot. Step 3: Construct the sweet spot factor and analyze the logging response characteristics to establish the sweet spot standard, where the sweet spot factor = movable porosity × movable saturation × brittle mineral content; Step 4: Select several other key core wells in the study area with complete logging series to verify the consistency of steps 1 to 3.

2. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 1, characterized in that: The special logging data in step 1 include nuclear magnetic resonance, downhole imaging and lithologic scanning.

3. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 1, characterized in that: The analytical data in step 1 include total organic carbon TOC, free hydrocarbon content S1, brittleness, porosity, saturation and maturity.

4. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 1, characterized in that: The sensitivity curve cross-plot in step 2 is the acoustic time difference AC-resistivity RT cross-plot.

5. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 1, characterized in that: In step 3, brittle mineral content = brittleness index × total mineral content.

6. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 5, characterized in that: The dessert standards in step 3 are as follows: The rules of Class I sweet spots are as follows: Natural gamma: 110-115 API, resistivity> 12Ω · m, acoustic wave delay 260-300 μs / m, movable porosity>3%, movable oil saturation>40%, brittleness index>50%, silty laminar felsic shale, oil recovery intensity>0.4t / (dm); The rules of Class II sweet spots are as follows: Natural gamma: 115-120 API, resistivity 6-12 Ω · m, acoustic wave delay 300-320μs / m, movable porosity 2-3%, movable oil saturation 30-40%, brittleness index 40-50%, felsic shale with muddy laminae and silty laminae, oil recovery intensity 0.2-0.4t / (dm); The rules of Class III sweet spots are as follows: natural gamma > 120API, resistivity < 6Ω · m, acoustic time difference >320μs / m, movable porosity <2%, movable oil saturation <40%, brittleness index <40%, clayey shale with argillaceous layers, and oil recovery intensity <0.2t / (dm).

7. The method for qualitatively identifying geological sweet spots in shale reservoirs according to claim 1, characterized in that: Step 5 is to summarize the sweet spot response characteristics of the conventional curve and establish a conventional curve identification sweet spot chart to promote the application to a certain area.

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