Areas Of Structural Complexity Research Articles

Characteristics and Controlling Factors of Methane Adsorption of the Longmaxi Shale in Northeastern Chongqing: Implications for Shale Gas Occurrence in Complex Structural Areas

Characteristics and Controlling Factors of Methane Adsorption of the Longmaxi Shale in Northeastern Chongqing: Implications for Shale Gas Occurrence in Complex Structural Areas

Study on Key Technologies of Geosteering for Shale Gas Horizontal Wells in the Complex Structural Area of Block H in Western Hubei-Eastern Chongqing.

Block H, located in western Hubei-eastern Chongqing, remains at a low exploration degree. Characterized by its complex structural attributes, the area presents adverse conditions such as a thin thickness of high-quality shale reservoir, rapid lateral formation occurrence, and poor stratigraphic correlation, challenging conventional geosteering methods. The primary shale gas reservoir in Block H corresponds to the Upper Permian Wujiaping Formation. To ensure that the shale gas horizontal wells in this block effectively penetrate high-quality gas reservoirs, this study delves into the geological characteristics of this stratigraphic unit, identifies principal challenges faced by current geosteering techniques, and introduces a tailored technical solution. This solution encompasses the application of real-time 3D geological modeling to track while drilling, identification of steering marker layers, optimization of steerable tools, and optimization of the steering trajectory while drilling. In the technology of optimization of the steering trajectory while drilling, a trajectory control calculation model based on the average angle technique was established for the first time. Additionally, a sectional control chart for marker layers and well inclination under different deflecting constraints was established. These methods have solved the problems of large error in target prediction and poor trajectory control effects by using the equal thickness method alone. The findings from this study can significantly enhance target prediction and trajectory control accuracy in complex structural areas, offering pivotal insights for the proficient development of analogous shale gas reservoirs in the future.

Adaptive fault enhancement in OVT domain based on anisotropy theory

As a result of the combined influence of multi-stage and multi-directional tectonic activities, the subsurface medium in complex structural areas can easily develop intricate fault systems with varying scales and directions. Post-stack seismic and azimuth-stack attributes have limited precision in recognizing such complex fault systems. In this paper, we propose an adaptive fault enhancement workflow in offset vector tile (OVT) domain based on anisotropy theory to improve the recognition ability of seismic data for multi-directional faults and minor faults. The vertical directions of fault strikes and tectonic strikes estimated by the gradient structure tensor (GST) can be used as sensitive observation azimuths of faults. At the same time, according to the anisotropic forward modeling and real data amplitude variation with offset (AVO) analysis of minor faults in marine shale of Wufeng-Longmaxi formations in Sichuan Basin, China, the incident angles with the largest difference between isotropic and anisotropic reflection coefficients can be used as sensitive incident angles of faults. A new fault enhancement seismic data can be reconstructed from the OVT gathers by traversing the sensitive azimuths and incident angles adaptively. The 3D model and real data indicate that the faults enhanced by the workflow we proposed are clearer in shape, smaller in scale, and richer in details, which is consistent with geology and well.

Development of All-electric Discharge Device for Working String

Most of the existing pipe string discharge devices in China are suitable for drilling operations, but some auxiliary devices for surface pipe string discharge in workover operations are not mature enough, and there are some problems such as inconvenient transportation, complex structure and large area. Based on the actual situation of small workover operation site, this paper puts forward the scheme of all-electric discharge device for well site operation pipe string, determines the structure function and work flow of the discharge device, carries out structural design for three parts of the lift, conveying device and pipe rack, and analyzes and calculates the structural parameters of the device. Through the static analysis of the main force components, the rationality of the device design is verified, and its structural strength is in line with the safe range.

川西龙门山复杂构造区精细模型构建和正演

川西龙门山复杂构造区精细模型构建和正演

Accumulation and exploration enlightenment of shallow normal-pressure shale gas in southeastern Sichuan Basin, SW China

Based on the drilling, logging, experimental and testing data of Well PD1, a shallow normal-pressure shale gas well in the Laochangping anticline in southeastern Sichuan Basin, the shallow shale gas reservoirs of the Ordovician Wufeng Formation to Silurian Longmaxi Formation (Wufeng–Longmaxi) were investigated in terms of geological characteristics, occurrence mechanism, and adsorption-desorption characteristics, to reveal the enrichment laws and high-yield mechanism of shallow normal-pressure shale gas in complex structure areas. First, the shallow shale gas reservoirs are similar to the medium–deep shale gas reservoirs in static indicators such as high-quality shale thickness, geochemistry, physical properties and mineral composition, but the former is geologically characterized by low formation pressure coefficient, low gas content, high proportion of adsorbed gas, low in-situ stress, and big difference between principal stresses. Second, shallow shales in the complex structure areas have the gas occurrence characteristics including low total gas content (1.1–4.8 m3/t), high adsorbed gas content (2.5–2.8 m3/t), low sensitive desorption pressure (1.7–2.5 MPa), and good self-sealing. Third, the adsorbed gas enrichment of shales is mainly controlled by organic matter abundance, formation temperature and formation pressure: the higher the organic matter abundance and formation pressure, the lower the formation temperature and the higher the adsorption capacity, which is more beneficial for the adsorbed gas occurrence. Fourth, the shallow normal-pressure shale gas corresponds to low sensitive desorption pressure. The adsorbed gas can be rapidly desorbed and recovered when the flowing pressure is reduced below the sensitive desorption pressure. Fifth, the exploration breakthrough of Well PD1 demonstrates that the shallow complex structure areas with adsorbed gas in dominance can form large-scale shale reservoirs, and confirms the good exploration potential of shallow normal-pressure shale gas in the margin of the Sichuan Basin.

Unchartered fault through outcrop study by using simple structure from motion technique in seismicaly active area

Structure from motion (SfM) is a photogrammetric method used to reconstruct 3-Dimensional (3D) surfaces from the displacement of the camera in between several 2-dimensional photographs. This method can produce sparse and dense point clouds from which high-resolution surface models such as digital surface models and digital terrain models are obtained. SfM is not restricted to topographic surfaces, it also can be used to model various ground objects at different scales such as trees, buildings, outcrops and any other structure that can be photographed with an ordinary camera. Among this myriad of possibilities, the present contribution focuses on the reconstruction of 3D outcrop models, as they can become digital archives of geological and seismic activity, especially in countries where landscape remodeling activity and mining are important. Outcrop is a vertical exposure of particular rock formation. By knowing the characteristics of the outcrop, we can understand the reservoir characteristics and important stratigraphic information. Also, we can take more attention on microstructural information for both slope instability and seismic characteristics analysis. Thus, although SfM is relatively new in geoscience, this study will provide the usage of the SfM technique to support the outcrop analysis to obtain important micro-structure information of the outcrop. Further, this data was used to support the seismic susceptibility assessment in a very complex geological structure area.

Explainable Supervised Machine Learning Model To Predict Solvation Gibbs Energy.

Many challenges persist in developing accurate computational models for predicting solvation free energy (ΔGsol). Despite recent developments in Machine Learning (ML) methodologies that outperformed traditional quantum mechanical models, several issues remain concerning explanatory insights for broad chemical predictions with an acceptable speed-accuracy trade-off. To overcome this, we present a novel supervised ML model to predict the ΔGsol for an array of solvent-solute pairs. Using two different ensemble regressor algorithms, we made fast and accurate property predictions using open-source chemical features, encoding complex electronic, structural, and surface area descriptors for every solvent and solute. By integrating molecular properties and chemical interaction features, we have analyzed individual descriptor importance and optimized our model though explanatory information form feature groups. On aqueous and organic solvent databases, ML models revealed the predictive relevance of solutes with increasing polar surface area and decreasing polarizability, yielding better results than state-of-the-art benchmark Neural Network methods (without complex quantum mechanical or molecular dynamic simulations). Both algorithms successfully outperformed previous ΔGsol predictions methods, with a maximum absolute error of 0.22 ± 0.02 kcal mol-1, further validated in an external benchmark database and with solvent hold-out tests. With these explanatory and statistical insights, they allow a thoughtful application of this method for predicting other thermodynamic properties, stressing the relevance of ML modeling for further complex computational chemistry problems.

A Numerical Study of Complex Impact Loads on Thin-Walled Casing of Aeroengine Considering Turbine Guide Vane Structure1

As the main load-bearing component of the aero-engine system, the thin-walled casings have the characteristics of large size, complex structure, thin wall, and large area. In addition to the harsh working environment, it is necessary to study applicable preventive measures to contain high-energy fragments to ensure flight safety. The complex load formed by the axial impact and circumferential torsion exerted by the turbine rotor on the exhaust casing is studied, and the model includes the turbine rotor. By analyzing the deformation and energy dissipation of the exhaust casing in the calculation results, the dynamic response of the power turbine and the exhaust casing in the complex impact load is obtained, and it is verified that the initial speed of the power turbine has no obvious relationship with the dynamic response and energy dissipation of the exhaust casing. At the same time, it is concluded that the axial velocity and aerodynamic force of the power turbine have a strong positive correlation with the complex impact load and dynamic response of the exhaust casing. In the follow-up studies and equivalent experiments, these conclusions can be used as a reference for further experimental design.

Quantitative evaluation of structural complexity in Shengquan minefield based on improved local linear embedding algorithm

Mine water disaster is closely related to the geological structure of the mine. A scientific evaluation of the complexity of the minefield structure can greatly contribute to mining safety. In this study, we optimized the fault impact index in the study area and proposed an improved local linear embedding (LLE) algorithm by investigating the Shengquan coal mine. We analyzed the fault formation age and connectivity between faults in the study area, combined with topology theory, and based on previous studies. The mechanical properties of faults and the influence of small faults on the strata can be combined to derive a quantitative evaluation model of the structural complexity of mines. Based on the evaluation model, the study area was divided into a simple structural area, a medium structural area, and a complex structural area. By comparing the location of water inrush points in recent years with the three-dimensional high-density electrical exploration of the 21,304 working face, the effectiveness and rationality of structural complexity zoning were determined.

Exploration and development in the Zhaotong national shale gas demonstration area: Progress and prospects

The Zhaotong national shale gas demonstration area in Yunnan (hereinafter referred to as demonstration area) is China's third largest national shale gas production base after Changning–Weiyuan in Sichuan and Fuling in Chongqing. And after more than ten years of deep and careful cultivation, a series of important achievements have been obtained in the exploration and development. From the perspective of exploration and development history, theory and technology, this paper systematically summarizes the exploration discovery process and productivity construction progress of shale gas in the demonstration area, expounds the geological exploration theories and key technologies of mountain shale gas, and predicts their development prospect and direction. And the following research results are obtained. First, the exploration and development in the demonstration area has gone through five development stages, and so far, three major productivity construction zones have been formed, including Huangjinba and Zijinba middle–deep shale gas zones and Taiyang shallow shale gas zone, with cumulative proved geological reserves more than 3100 × 108 m3 and cumulative gas production more than 72 × 108 m3. It has been constructed into the third largest green shale gas demonstration base in China. Second, the “multi-field coordination and multi-element coupling” mountain shale gas enrichment, accumulation and occurrence theory of “sedimentary background controlling source rock and reservoir, reworking intensity controlling preservation, and three-dimensional sealing controlling enrichment” is put forward innovatively, and the “three-dimensional sealing system” accumulation model of extrabasinal shallow shale gas is established. Third, a series of zone selection and evaluation technologies for mountain shale gas in strongly reworked complex structural areas have been developed, and the concept of geology–engineering integration has first been adopted to create transparent shale gas reservoirs and cultivate high-yield wells. A major exploration breakthrough has been achieved from marginal basin medium deep shale gas layers to extrabasin ultra shallow to medium shallow ones, and domestic first large-scale monoblock shallow shale gas field with reserves over 2570 × 108 m3 has been discovered. Fourth, a landmark technological achievement and efficient development model with geology–engineering integration and shale geomechanical evaluation as the core has been formed, which leads the clean, green and efficient exploration and development of mountain shale gas. In conclusion, it is necessary to implement the exploration strategic idea of “two outgoing” in the demonstration area, i.e., “walking out of the stable area of the basin and marching into the complex structure areas in the Dianqianbei Depression” and “walking out of the Wufeng–Longmaxi Formation and exploring other layers for breakthrough”. What's more, it is recommended to carry out the double-layer stereoscopic horizontal well pattern deployment of “Leping Formation CBM (coal measure gas) + Longmaxi Formation shale gas” appropriately in a large scale, so as to establish a new integrated development model for the three-dimensional efficient development of mountain shale gas and CBM.

Lithofacies Types and Reservoir Characteristics of Mountain Shale in Wufeng Formation-Member 1 of Longmaxi Formation in the Complex Structural Area of Northern Yunnan-Guizhou.

The mountain shale in Wufeng Formation-Member 1 of Longmaxi Formation in the complex structural area of northern Yunnan-Guizhou has great potential for exploration and development. In order to clarify the differences of reservoir quality and the longitudinal distribution law of different lithofacies, the lithofacies in Wufeng Formation-Member 1 of Longmaxi Formation was divided combined with core, logging, and analytical test data. Based on the data of total organic carbon, laminate structure, reservoir porosity types and physical properties, and gas content, the reservoir characteristics and advantageous lithofacies shale reservoir distribution were determined. The results show that the mountain shale lithofacies in the study area are divided into 7 major types and 20 subtypes. The high-carbon siliceous shale has the highest degree of organic pore development, specific surface area (average 28.55 cm2/g), and pore volume (average 0.0397 cm3/g). Two types of advantageous lithofacies shale reservoir in the study area were identified. The high-carbon siliceous shale reservoir could be considered as an excellent shale reservoir for shale gas and is mainly concentrated in the first section. It is mainly developed in layer-1 and the bottom of layer-2 of the Longmaxi Formation, providing favorable source-reservoir conditions for shale gas enrichment. The medium-carbon siliceous shale, medium-carbon clay siliceous shale, and medium-carbon calcareous siliceous shale, developed in the top of layer-2 and the bottom of layer-3 of the Longmaxi Formation, are assumed to be moderately promising for shale gas. Therefore, the research results deepen the understanding of the longitudinal distribution of the dominant shale reservoirs in the study area and are of great significance in promoting strategic transfer of the main shale gas exploration system in the south from the Sichuan basin to the outer basin.

Variations of Pore Structure and Methane Adsorption of Continental Deformed Shales from Small-Scale Anticline and Syncline: Two Cases Study of the Triassic Yanchang Formation, Ordos Basin and Jurassic Yaojie Formation, Minhe Basin.

In order to investigate the effect of tectonic compression on pore structures and methane adsorption capacity, the continental deformed shales are collected from the Rujigou section in the Ordos Basin and the Hongshawan section in the Minhe Basin as research objects. The porosity, N2 and CO2 adsorption, field emission scanning electron microscopy (FE-SEM), and methane isothermal adsorption experiments are used to investigate the pore structure and methane adsorption of continuous deformation shales. Combined with formation curvature, the quantitative correlations between tectonic compression deformation and reservoir structure parameters and methane adsorption are analyzed. The interlayer pore, intergranular pore, dissolution pore, and microfracture are developed, and the amounts of microfractures are obviously higher in anticlinal cores than that of the anticlinal wings. The porosities for the Rujigou and Hongshawan sections are 2.1-4.73% (avg 3.21%) and 1.49-9.05% (avg 4.80%), respectively. The corresponding mesopore volume, specific surface area, and average diameter for the Rujigou section are 0.022-0.038 cm3/g, 12.35-14.30 m2/g, and 8.76-11.21 nm and for the Hongshawan section are 0.0033-0.0052 cm3/g, 0.376-0.875 m2/g and 21.61-36.37 nm, respectively. The corresponding micropore specific surface area and pore volume for the Rujigou section are 11.301-16.068 m2/g and 0.0033-0.0051 cm3/g and for the Hongshawan section are 10.951-15.912 m2/g and 0.0043-0.0058 cm3/g, respectively. The methane adsorption capacities for the Rujigou and Hongshawan sections are 2.76-3.82 mg/g and 1.62-2.135 mg/g, respectively. The porosity, mesopore and micropore structure parameters, and methane adsorption capacity in synclinal core are lower than those in synclinal wings. However, the above tendency is reversed for the anticline, whose adsorption capacity in the anticlinal core is higher than that in anticlinal wings. There exist high correlations between formation curvature and pore structure, physical property, and methane adsorption, indicating that formation curvature has a significant effect on the shale reservoir. By combining theoretical maximum adsorbed gas and free gas results, it implies that the anticlinal core undergoing moderate structural compression deformation can provide more methane adsorption sites and reservoir space, which is the shale gas favorable accumulation area. This study could provide beneficial references for continental shale gas exploration and evaluation in complex structure areas.

Hydrogeochemical and geophysical investigations to delineate underground water aquifer in arid regions: A case study, Gara oasis, Egypt

The goal of the present study is to investigate, delineate, and evaluate the shallow Miocene groundwater aquifer with vertical and lateral facies variations in the Gara oasis, western desert of Egypt. This oasis represents a typical arid region in North Africa. Through grid texture analysis, lineament detection, edge detection, thresholding, and identifying areas of structural complexity from the filtered residual reduced-to-pole magnetic anomaly map, it is possible to outline the fracture zones that principally control the groundwater aquifers and water flow in the area. The groundwater quality and quantity are examined hydro-geochemically through nine groundwater samples that were gathered from wells and springs distributed throughout the area around Gara Lake. Measurements of physio-chemical parameters (TDS, pH, and EC) are carried out and its spatial distribution is critically studied. The results reveal that the ion-exchange process caused by water-rock interaction is the dominant process. Furthermore, the main ions in the groundwater in the study areas were Na and Cl. This might be due to evaporation or halite dissolution with the upward flow of waters through the fractures from the deep aquifer of the Nubian sandstone to the shallow aquifer of the fractured Miocene limestone.

Uniform and Competency-Based 3D Keypoint Detection for Coarse Registration of Point Clouds with Homogeneous Structure

Recent advances in 3D laser scanner technology have provided a large amount of accurate geo-information as point clouds. The methods of machine vision and photogrammetry are used in various applications such as medicine, environmental studies, and cultural heritage. Aerial laser scanners (ALS), terrestrial laser scanners (TLS), mobile mapping laser scanners (MLS), and photogrammetric cameras via image matching are the most important tools for producing point clouds. In most applications, the process of point cloud registration is considered to be a fundamental issue. Due to the high volume of initial point cloud data, 3D keypoint detection has been introduced as an important step in the registration of point clouds. In this step, the initial volume of point clouds is converted into a set of candidate points with high information content. Many methods for 3D keypoint detection have been proposed in machine vision, and most of them were based on thresholding the saliency of points, but less attention had been paid to the spatial distribution and number of extracted points. This poses a challenge in the registration process when dealing with point clouds with a homogeneous structure. As keypoints are selected in areas of structural complexity, it leads to an unbalanced distribution of keypoints and a lower registration quality. This research presents an automated approach for 3D keypoint detection to control the quality, spatial distribution, and the number of keypoints. The proposed method generates a quality criterion by combining 3D local shape features, 3D local self-similarity, and the histogram of normal orientation and provides a competency index. In addition, the Octree structure is applied to control the spatial distribution of the detected 3D keypoints. The proposed method was evaluated for the keypoint-based coarse registration of aerial laser scanner and terrestrial laser scanner data, having both cluttered and homogeneous regions. The obtained results demonstrate the proper performance of the proposed method in the registration of these types of data, and in comparison to the standard algorithms, the registration error was diminished by up to 56%.

Water-gas combined methane control in low permeability coal seam near fault: a case study

ABSTRACT Coal and gas outburst (CGO) is one of the most devastating disasters in underground coal mines, and it always triggers substantial casualties and property losses. Therein, the coal seam permeability and gas extraction rate are usually low in tectonic coal reservoirs, threatening safe coal production activities. In this work, water-gas combined methane control technology was proposed, based on the merits of hydraulic fracturing (HF) and liquid CO2 phase change fracturing (LCPCF), to improve the permeability of tectonic coal reservoirs. A field experiment was then conducted in a coal seam near a fault to verify its technical practicality, and the tectonic coal seam gas governance effect was accordingly evaluated. The research results suggested that the maximal concentration and average concentration of a single drill hole after HF increased by 13 times and 3 times, respectively, while the maximal flow and average flow increased by 23.4 times and 24.7 times, respectively. On the other hand, the peak concentration and mean concentration of a single hole after LCPCF increase by 2.7 times and 3 times, respectively, and the peak flow and mean flow increase by 6 times and 6.6 times, respectively. Additionally, the destructive degree triggered by LCPCF can be intuitively quantified through grayscale analysis. Furthermore, through the application of water-gas combined methane control technology in engineering practice, the gross quantity of extracted gas is 11 times larger than when LCPCF or HF is individually conducted, and the mean concentration and flow are 1.9 times greater and 2.1 times greater, respectively, than when LCPCF or HF is separately performed, indicating that this technology is practical and has a superior tectonic coal seam permeability improvement effect. This study has profound implications for enhancing coalbed methane (CBM) recovery and for eliminating CGO disasters in tectonic coal reservoirs or complex geologic structure areas.

Effects of Fracture Formation Stage on Shale Gas Preservation Conditions and Enrichment in Complex Structural Areas in the Southern Sichuan Basin, China

Fractures have significantly impacted the preservation, enrichment, and productivity of shale gas in the Longmaxi Formation in the complex structural area of the southern Sichuan Basin. Based on outcrop, core, imaging logging, inclusion analysis, acoustic emission experiments, and burial and thermal evolution history data, the formation stage, evolution and preservation conditions of structural fractures were comprehensively studied. Shear fractures are the main features of tectonic origin and are characterized by small widths, wide spacing, and high filling degrees. The structural fractures of the Longmaxi Formation can be divided into three groups in terms of their formation stage. The first-stage fractures were formed in the middle-late period of the Yanshanian tectonic movement (86.2–68.5 Ma), when the palaeotectonic stress was 68.33–71.82 MPa; and the homogenization temperature of the fluid inclusions in the corresponding fracture fillings is 150–178°C. The second-stage fractures were formed at the end of the Yanshanian -early Himalayan tectonic movement (68.5–35.2 Ma), when the palaeotectonic stress was 85.2–100.5 MPa; the homogenization temperature of the corresponding fluid inclusions is 123–148°C. The third-stage tectonic fractures formed during the middle-late period of the Himalayan tectonic movement (35.2–0 Ma), when the palaeotectonic stress was 55.6–63.8 MPa; fillings are scarce in these fractures, but the measured homogenization temperature of the corresponding fluid inclusions is 90–110°C. Shale gas preservation conditions were affected by the fracture formation stage, maximum horizontal crustal stress, fault scale, structural burial depth, formation pressure coefficient, etc. Three types of favourable preservation conditions were identified. The Type I target area is the low slope area in the middle of the syncline, which occurs more than 2.0 km from the fault. The research results have guiding significance for the evaluation of the preservation conditions of deep shale gas in the study area and similar areas.

Geometry and Kinematics Characteristics of Strike-Slip Fault Zone in Complex Structure Area: A Case Study From the South No. 15 Strike-Slip Fault Zone in the Eastern Sichuan Basin, China

The eastern Sichuan Basin has undergone multiple stages of tectonic evolution and shows complex structural characteristics. It is found that there are a series of NW-SE base-trending strike-slip faults in this area besides NE-SW strike-blocking structures. There are almost no previous studies on strike-slip faults in the eastern Sichuan Basin. This paper fills in the blank of geometry and kinematics research on the strike-slip fault zone in this area. Based on highly precise 3D seismic section, coherent attribute slice and time slice, the geometric and kinematic characteristics of the fault are analyzed. The dynamic characteristics are analysed based on the structural style of the superimposed development model and the nature and activity intensity of strike-slip faults in different periods. and it was found that No. 15 strike-slip fault was a large basement strike-slip fault. The research results show that the profile of the No. 15 strike-slip fault mainly shows a subvertical fracture, positive flower structure and negative flower structure and a composite flower structure with positive and negative flower structures superimposed on each other in the upper and lower planar sections with linearly outspread and zonal distribution characteristics; spatially, there is a “ribbon” effect and a “dolphin” effect. the left strike-slip distance of the TS interface is 0.462 km, and the right strike-slip distance of the TP2 interface is 0.782 km. The strike-slip fault experienced at least three active stages of superimposed deformation during its formation and reconstruction, among which episode II in the middle Caledonian movement was the main active stage of the No. 15 strike-slip fault zone. This study of the structural style and genetic mechanism of a strike-slip fault zone is of guiding significance to the exploration and development of strike-slip fault-controlled reservoirs in the study area.

Normal Pressure Shale Gas Preservation Conditions in the Transition Zone of the Southeast Basin Margin of Sichuan Basin

Shale in the Wufeng Formation of the upper Ordovician and Longmaxi Formation of lower Silurian in the Sichuan Basin and its surrounding area is widespread. Shale gas resources are abundant. Shale gas in the Wufeng Formation and the Longmaxi Formation in the basin has been a major breakthrough. The basin margin transition zone in southeastern Chongqing is in an intense tectonic activity area, which is more complicated and special than the stable stratum in the basin. Therefore, it is necessary to put forward higher requirements for preservation conditions and enrichment pattern evaluation of shale gas. Therefore, in view of the complicated structural pattern of the basin margin transition zone in southeastern Chongqing, the preservation conditions and reservoir forming patterns are analyzed through structural evolution, uplift and denudation, fault development, structural styles, roof and floor conditions, and formation pressure. The results show that the main reason for the formation of normal pressure is the late uplift, denudation and fault development. The pressure coefficient from the basin to the outer layer is changed from overpressure to normal pressure, and structural transformation forms the preservation form of shale gas with narrow and steep residual anticline, wide residual syncline and residual slope. The preservation condition evaluation of normal shale gas should be based on structural factors such as structural evolution, structural style, uplift and denudation degree and fault development degree, with formation pressure coefficient as reference condition, combined with material basic conditions such as roof and floor conditions and formation thickness. The findings of this study can help for better understanding of the “sweet spot” prediction of normal pressure shale gas in complex structural area.

3D structural modeling for seismic exploration based on knowledge graphs

Three-dimensional structural models provide valuable references for studying exploration challenges and often are used for survey design and seismic method validation as well as to assist with reservoir interpretation. The current structural modeling strategy primarily relies on seismic images, which can suffer from degraded image quality in areas of complex structures. This leads to less-reliable structural interpretations. It is difficult to build appropriate models with unreliable inputs by data-driven modeling methods when the input data contain no other constraints. To mitigate this problem, we have adopted a knowledge-data-driven structural modeling method for seismic exploration based on knowledge graphs that contain certain digitized prior information related to the subsurface structures. The knowledge graph of the structural models formalizes the knowledge of geoscientists by describing the structural model entities and their interrelations in the form of a graph. We first establish the knowledge graph of the structural model to constrain the model topology, then estimate the geologic intersections (lines) between the geologic surfaces under the guidance of the knowledge graph, and finally reconstruct the surfaces under the constraints of the intersections and generate closed geologic bodies. The knowledge graph defines the overall structure of the model, which sets up a priori constraint for the modeling and plays a role in transferring expertise to computers. We use two field models to demonstrate our structural modeling process and prove the effectiveness and feasibility of the method.