Changling shale lithofacies cause analysis method based on hydrodynamic force and environmental factor conditions

Abstract

The invention belongs to the technical field of unconventional shale oil and gas exploration and development, and discloses a Changling shale lithofacies cause analysis method based on hydrodynamic force and environmental factor conditions. Comprising the following steps: finely describing a rock core, determining lithologic characteristics of shale in a Changling region, determining a lithofacies division scheme by four end members of lithologic-structure-TOC-mineral, analyzing formation causes of a clay texture layer and a silt texture layer under a hydrodynamic condition, analyzing hydrodynamic conditions formed by each lithofacies, and analyzing environmental factor conditions formed by each lithofacies. And summarizing the comprehensive cause of each lithofacies. According to the method, the formation cause of lithofacies is analyzed under the two conditions of hydrodynamic force and environmental factors, the first-stage and second-stage shale formation mechanism of the Songliao basin Changling ridge depressed green is explained in a multi-dimensional mode, and a foundation is laid for deposition characteristics, reservoir forming modes, oil and gas enrichment rules and dessert evaluation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of unconventional shale oil and gas exploration and development, and particularly relates to a Changling shale facies genesis analysis method based on hydrodynamic force and environmental factor conditions. BACKGROUND

[0002] Shale oil and gas is the focus of unconventional exploration in various countries in the world. Many studies have been conducted on shale lithology and facies identification at home and abroad. Facies genesis is crucial to the study of sedimentary characteristics, reservoir forming mode and oil and gas enrichment regularity. Therefore, shale facies genesis analysis must be intensively researched.

[0003] Shale has the characteristics of complex mineral composition, fine particles, rich organic matter and strong heterogeneity. Therefore, shale facies division and facies genesis mechanism research are the basis for the study of sedimentary characteristics, reservoir forming mode, oil and gas enrichment regularity and sweet spot evaluation. SUMMARY

[0004] In order to overcome the shortcomings of the prior art, the application provides a Changling shale facies genesis analysis method based on hydrodynamic force and environmental factor conditions. The method is researched from the aspects of hydrodynamic force condition and environmental factor, supports the further implementation of sweet spot layer and sweet spot area, and lays a foundation for the evaluation of shale sedimentary characteristics, reservoir forming mode, oil and gas enrichment regularity and sweet spot.

[0005] The above object of the application is achieved by the following technical scheme: a Changling shale facies genesis analysis method based on hydrodynamic force and environmental factor conditions, comprising the following steps:

[0006] 1. Fine core description to determine the shale lithological characteristics in the Changling area;

[0007] 2. Determine the facies division scheme by using the four end members of "lithology-structure-TOC-mineral", and clarify the facies types and characteristics;

[0008] 3. Analyze the genesis of clayey lamination and silt lamination under the condition of hydrodynamic force;

[0009] 4. Analyze the hydrodynamic force condition for the formation of each facies;

[0010] 5. Analyze the environmental factor condition for the formation of each facies;

[0011] 6. Summarize the comprehensive genesis of each facies.

[0012] Further, the shale lithological characteristics determined in step 1 include color, composition, structure and structure.

[0013] Further, the lithology in step 2 is divided by using the three end members of mud / shale-silt-carbonate rock, and each axis is divided by 50%.

[0014] Further, the step 2 is constructed by adopting block, laminated and layered three types of construction.

[0015] Further, the step 2 is divided according to the TOC value, and is divided into three types of high organic matter content, medium organic matter content and low organic matter content, wherein the TOC value of the high organic matter content is greater than 2%, the TOC value of the medium organic matter content is 1%-2%, and the TOC value of the low organic matter content is less than 1%.

[0016] Further, the step 2 is divided according to the TOC value, and is divided into three types of high organic matter content, medium organic matter content and low organic matter content, wherein the TOC value of the high organic matter content is greater than 2%, the TOC value of the medium organic matter content is 1%-2%, and the TOC value of the low organic matter content is less than 1%.

[0017] The beneficial effects of the present application compared with the prior art are: the formation mechanism of the shale of the first and second members of the Qinglong Formation in the Changling Sag of the Songliao Basin is analyzed under the conditions of hydrodynamic force and environmental factors, the formation mechanism is explained in multiple dimensions, and the foundation is laid for the sedimentary characteristics, the accumulation mode, the oil and gas enrichment rule and the sweet spot evaluation. BRIEF DESCRIPTION OF DRAWINGS

[0018] The present application will be further described below in combination with the drawings and specific embodiments

[0019] Figure 1 is a schematic diagram of shale lithology characteristics;

[0020] Figure 2 is a schematic diagram of lithofacies division scheme;

[0021] Figure 3 is a schematic diagram of high organic matter mud laminated clay shale facies characteristics;

[0022] Figure 4 is a schematic diagram of medium-high organic matter mud laminated felsic shale facies characteristics;

[0023] Figure 5 is a schematic diagram of medium-low organic matter silty sand laminated felsic shale facies characteristics;

[0024] Figure 6 is a schematic diagram of the development characteristics of the paleosalinity and redox condition environmental factors. DETAILED DESCRIPTION

[0025] The present application will be further described below in combination with the drawings and specific embodiments

[0026] Example 1

[0027] A shale lithofacies genesis analysis method based on hydrodynamic force and environmental factors, comprising the following steps:

[0028] Step 1: Detailed core characterization to determine the lithologic characteristics of shale in the Changling area

[0029] Lithology most directly reflects the characteristics of rocks, including color, composition, texture, and structure. Through core observations from 14 wells in the study area, combined with laboratory thin section identification, four main lithologies were identified in the Qingshankou Formation in the study area: shale, siltstone, calcareous limestone, and dolomite. Shale is prevalent in the Qing Member of the Qingshankou Formation in southern Songshan. It is gray-black and dark gray in color, with a mud-grade particle content of more than 50% (particle size <0.004mm), and a small amount of silt-grade particles. The composition is mainly clay minerals, with small amounts of felsic minerals and other minerals (pyrite, etc.). Horizontal bedding is commonly developed, consisting of alternating clayey, felsic, and organic laminae. Locally, it contains ostracod and ostracod fossils, and lamellae are well developed.

[0030] Step 2: Determine the lithofacies division scheme based on the four-terminal elements of "lithology-structure-TOC-minerals" to clarify the lithofacies type and characteristics

[0031] The lithology is divided into three types: mud / shale, siltstone and limestone (cloudstone) using the three-terminal division of mud / shale, siltstone and limestone with the 50% boundary of each axis. The primary structure is divided into three types: massive, laminated and layered. The mineral composition is divided into three types: clay, felsic and limestone using the three-terminal division of clay, felsic and carbonate with the 50% boundary of each axis. The fine-grained sediments are divided into three types according to the TOC value: high organic matter content (TOC value greater than 2%), medium organic matter content (TOC value 1%-2%) and low organic matter content (TOC value less than 1%). Based on the above division scheme, the shale lithofacies in the study area are mainly divided into three types: high organic matter mud-grade laminated clay shale, medium-high organic matter mud-grade laminated felsic shale, and medium-low organic matter silt-containing laminated felsic shale. Clayey shale facies with high organic matter, muddy-grade laminae, is widespread in the Tahucheng District and Yuzijing Districts of the study area. These facies are gray-black in color, with straight and continuous laminae. Muddy-grade laminae are predominant, organic-rich clay laminae, with minimal silt laminae. Clay mineral content is ≥50%. Laminae are less than 1 mm thick and predominately dark. Due to the high degree of thermal evolution, the color difference between organic-rich and poor clay laminae is less pronounced after hydrocarbon expulsion, resulting in an overall dark color. Fluorescence is poor, and laminae density is high, often exceeding 3,000 per meter. Organic matter abundance is high, with TOC ≥2%, and the primary sedimentary environment is deep lake. Felsic shale with medium-to-high organic matter, muddy-grade laminae, is widespread in the study area. These facies are dark gray and gray-black in color. Laminae are straight, continuous, or discontinuous, with muddy-grade laminae predominating, and silt-grade laminae (≤10%) present. Felsic mineral content is ≥50%. The thickness of the laminae is less than 2 mm, with dark laminae interbedded with light laminae, and the light laminae are clear. The laminae density is relatively large, ranging from 1000 to 3000 laminae / m. The organic matter abundance is medium to high, with TOC ≥1%, and the main sedimentary environment is semi-deep lake to deep lake. The medium-low organic matter silt-laminae-containing felsic shale is mainly developed in the lower part of the Qing 1st Member and the Qing 2nd Member. It is dark gray and gray in color, with wavy, continuous-intermittent laminae. The laminae are mainly composed of mud-grade laminae interbedded with silt-grade laminae, and the silt-grade laminae content is between 10% and 50%. The laminae thickness is mostly >1 mm, and the felsic mineral content is ≥50%. The interface between the light and dark laminae is clear, with good fluorescence, and most of them have deformation or sedimentary dyke structures. The laminae density is relatively low, with the main body less than 1000 laminae / m. The organic matter abundance is relatively low, with TOC <2%, and the main sedimentary environment is the pro-delta.

[0032] Step 3: Analyze the origin of clay and silt laminae under hydrodynamic conditions

[0033] Cause of clayey lamination: When fine-grained sediment is suspended in water, it carries an electric charge of a certain sign due to surface physical and chemical reactions, attracting surrounding ions and water molecules of opposite signs to tightly surround it and form an adsorbed water film, which approaches each other to form flocs. When clay is deposited as flocs, one mode is suspended sedimentation. This process primarily occurs in the still waters of the lake center, where it co-deposits with organic matter, forming clayey shales with varying degrees of organic richness and poorness. This primarily forms coupled organic-rich clayey laminae. Furthermore, fine particles carried by rivers, wind, and atmospheric dust and aerosols migrate to the center of the lake basin as suspended matter through circulation and mixed diffusion. During this process, coarser particles settle first due to reduced water velocity, while finer clay and organic matter remain dispersed and concentrated within the thermocline. Changes in climate, temperature, salinity, and biological activity disrupt the thermocline, disrupting equilibrium and increasing the static sedimentation flux of suspended matter. Under conditions of water stratification, suspended matter is preserved, ultimately forming seasonal and climatically related clayey laminae. This often results in a coupled combination of clayey laminae intercalated with felsic laminae. The second mode is the "advection transport" mode. Clay materials can form flocculent ripples and migrate without being destroyed, breaking the limitation that clay materials can only be deposited under low-energy static water conditions. These flocculent ripples migrate downstream through the continuous collapse and foredeposition of lobes, with low-angle inclined laminae within them. However, due to the 30-40 μm spacing between the felsic shale laminae containing medium-low organic matter and silt during their bottom flow, once fully compacted after deposition, the inclined thin layers within the ripples become unrecognizable, ultimately forming parallel clay laminae.

[0034] Origin of felsic laminae: Felsic sediments are typical non-cohesive particles, and the sedimentation process complies with Stock's law. When felsic debris is transported into the lake basin by terrigenous rivers, it is affected by the combined effects of gravity, buoyancy, drag force caused by bottom shear, and uplift force. When the hydrodynamic force of the load weakens, the particle movement speed decreases, and gravity gradually becomes dominant, the felsic sediments undergo mechanical differentiation near the shore and settle to form massive siltstone and felsic mudstone with wavy bedding or low-angle cross-bedding.

[0035] Step 4: Analysis of hydrodynamic conditions for the formation of each lithofacies

[0036] This study focused on shale hydrodynamic conditions, focusing on grain size analysis. Grain size analysis reveals that clayey shales with high-organic-matter mud-grade laminae are primarily composed of mixed clay-organic flocculent deposits, containing very few terrigenous clastic particles. Clay and organic matter are primarily deposited in uniform suspension, while approximately 10% of the clastic particles are in graded suspension, and less than 5% are in uniform suspension, indicating low-density hydrostatic deposition. Felsic shales with medium-to-high-organic-matter mud-grade laminae often exhibit clastic-rich laminae, where grains are primarily transported in graded suspension, with reduced flocculent sediments. The graded suspension fraction is approximately 40%, the uniform suspension fraction is approximately 20%, and the overall suspended particle content exceeds 60%. Shales with medium-to-low-organic-matter silt-bearing laminae exhibit clastic-rich laminae, where grains are primarily silt-grade and are primarily transported in graded suspension, with a graded suspension fraction exceeding 50%. This indicates strong transport dynamics, suggesting a turbidite origin, with scour structures visible in both cores and thin sections.

[0037] Step 5: Analysis of environmental factors and conditions for the formation of each lithofacies

[0038] (1) Paleoclimate factor: The fine-grained organic-rich deposits of the Qingshankou Formation were mainly formed in a stable tectonic subsidence, but in the period of rapid lake-level rise, the paleoenvironmental temperature was relatively high, and the paleoclimate background was relatively high humidity. The lithofacies of high-organic-matter argillaceous laminae mudstone and high-organic-matter argillaceous laminae felsic shale were mostly formed in a continuous humid environment; the lithofacies of high-organic-matter argillaceous laminae felsic shale and medium-low-organic-matter silty laminae felsic shale were mostly formed in a dry-wet alternating environment under the background of warm and humid, especially after the relative drought, the strong rainfall promoted the development of silty laminae; (2) Paleosalinity and preservation condition factor: Compared with other organic-rich shale formations such as Nenjiang Formation, the water salinity of the Qingshankou Formation was relatively high, and the overall performance was a semi-saline water-saline water environment, which also had good preservation conditions. The lithofacies of high-organic-matter argillaceous laminae mudstone and high-organic-matter argillaceous laminae felsic shale were mostly formed in a semi-saline water environment, which was probably caused by the reduction of water salinity due to continuous rainfall, and the water bottom was basically in reducing conditions. The lithofacies of high-organic-matter argillaceous laminae felsic shale and medium-low-organic-matter silty laminae felsic shale were mostly developed in a semi-saline water-saline water environment, which was affected by the relative drought of the paleoclimate, and was formed in a strong reducing water condition due to the influence of high salinity. This shows that the Qingshankou Formation has excellent preservation conditions during the deposition of Q1-Q9, and the preservation condition is not the key factor controlling the enrichment of organic matter; (3) Biological productivity factor: The key factors affecting the enrichment of organic matter in fine-grained sedimentary rocks are preservation conditions and organic matter sources (biological productivity). The lake had high productivity when the lithofacies of high-organic-matter argillaceous laminae mudstone and high-organic-matter argillaceous laminae felsic shale were formed; the lake productivity fluctuated relatively greatly when the lithofacies of high-organic-matter argillaceous laminae felsic shale and medium-low-organic-matter silty laminae felsic shale were formed, which had both extremely high and low lake productivity. This shows that under the background of high productivity and good preservation conditions, the effective accumulation of organic matter and the coupling of various sediment minerals are the key to the deposition of various types of lithofacies

[0039] Step 6: Summarize the comprehensive genetic analysis of each lithofacies

[0040] High-organic-matter argillaceous laminae mudstone: The laminae composition is poor and rich organic matter argillaceous laminae, and the poor and rich organic matter argillaceous laminae are coupled. From the formation process, it is mainly formed in a deep lake environment, which is far away from the delta and turbidity current source supply, and its clay minerals mainly come from suspension and sedimentation, and lack of felsic material supply. At the same time, a large number of dead plankton algae in the deep lake area also deposit together with clay through suspension and sedimentation, and are preserved under the storm wave surface to form high-organic-matter argillaceous laminae mudstone;

[0041] High-medium organic mud-grade laminae felsic shale: This shale has a high organic matter content and is characterized by predominantly mud-grade laminae, with clay-dominated laminae and a small amount of silt-grade laminae. The silt-grade material is primarily carried by lake currents, wind, atmospheric dust, and aerosols, migrating to the center of the lake basin as suspended matter through circulation (bottom currents) and mixed diffusion. During this process, coarser particles continuously settle from the thermocline due to reduced water velocity, forming silt-grade laminae, where cross-bedding reflecting water flow conditions can be seen. Finer mud-grade particles and organic matter, however, are concentrated in a dispersed, suspended state within the thermocline. Changes in climate, temperature, salinity, and biological activity lead to the disappearance of the thermocline, disrupting equilibrium and increasing the static settling flux of suspended matter. These particles are preserved under conditions of water stratification, ultimately forming mud-grade laminae related to season and climate. Furthermore, the environment in which this lithofacies formed had a certain oxygen content, which consumed organic matter to a certain extent, resulting in the formation of high-medium organic mud-grade laminae felsic shale.

[0042] Low- to medium-organic matter felsic shale with silt-grade laminae: This shale has a relatively low organic matter content and contains a moderate amount of silt-grade laminae (10%-50%). This lithofacies primarily forms in areas of turbidity current development and is closely related to turbidity current activity. Gravity sliding re-transports delta-front sand bodies, transporting them long distances along the lakebed as bedload along with mud-grade clay flocs. As flow velocity decreases, silt-grade laminae are deposited, and mud-grade flocculent ripples continue to migrate downstream. As flow velocity decreases further, sedimentation occurs. Low-angle inclined laminae are present within the ripples during deposition, but compaction after deposition makes the inclined thin layers within the ripples unrecognizable. Sedimentary structures related to compaction and drainage, such as sand balls and sluice structures, are visible. Furthermore, the large amounts of oxygen introduced by turbidity currents deplete organic matter, resulting in the formation of low- to medium-organic matter felsic shale with silt-grade laminae.

[0043] The above-established lithofacies genetic analysis method for the Changling shale, based on hydrodynamic and environmental factors, establishes a multi-dimensional analysis of its lithofacies genetic mechanism. This lays the foundation for sedimentary characteristics, reservoir formation patterns, oil and gas enrichment patterns, and sweet spot evaluation, and has important scientific guidance for the review of old wells and the exploration of unconventional oil and gas resources.

[0044] The above-described embodiments are only preferred embodiments of the present invention, and are not intended to be all feasible embodiments of the present invention. Any obvious modifications made by a person skilled in the art without departing from the principles and spirit of the present invention should be considered to be included within the scope of protection of the claims of the present invention.

Claims

1. A method for analyzing the lithofacies genesis of Changling shale based on hydrodynamic and environmental factors, characterized in that: The following steps are involved: S1. Detailed core characterization to determine the lithologic characteristics of shale in the Changling area; S2. Determine the lithofacies classification scheme based on the four-terminal elements of "lithology-structure-TOC-minerals" to clarify the lithofacies types and characteristics; S3. Analysis of the genesis of clayey and silty laminae under hydrodynamic conditions; S4. Analysis of hydrodynamic conditions for the formation of each lithofacies; S5. Analysis of environmental factors and conditions for the formation of each lithofacies; S6. Summarize the comprehensive genesis of each lithofacies.

2. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 1 is characterized in that: The shale lithologic characteristics determined in step S1 include color, composition, texture, and structure.

3. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 1 is characterized in that: In step S2, the lithology is divided using the three-terminal element of mud / shale, silt sand and carbonate rock, with each axis being divided by 50%.

4. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 1 is characterized in that: The structure in step S2 adopts three structural types: blocky, lamellar and layered.

5. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 1 is characterized in that: The TOC classification standard in step S2 is based on the TOC value, which is divided into three types: high organic matter content, medium organic matter content and low organic matter content.

6. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 5 is characterized in that: The TOC value of the high organic matter content is greater than 2%.

7. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 5 is characterized in that: The TOC value of the medium organic matter content is 1% to 2%.

8. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 5 is characterized in that: The TOC value of the low organic matter content is less than 1%.

9. The petrographic analysis method of Changling shale based on hydrodynamic and environmental factors according to claim 1 is characterized in that: In step S2, the minerals are divided into three end members: clay, felsic, and carbonate, with each axis being divided by 50%.

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