Distribution Of Tectonic Fractures Research Articles

Characteristics and Controlling Factors of Natural Fractures in Deep Carbonates of the Puguang Area, Sichuan Basin, China.

Understanding the types, characteristics, and controlling factors of natural fractures in deep and ultradeep carbonates is crucial for evaluating reservoir quality, optimizing well deployment, and comprehending their impact on hydrocarbon exploitation. Multiple types of natural fractures are widespread in the deep carbonates of the Feixianguan Formation in the Puguang area, northeastern Sichuan Basin, China, and the main controlling factors are complex. Based on geological, geophysical, and experimental data, this study defined fracture types and analyzed the fracture development characteristics in the deep Feixianguan carbonates. On this basis, the main geological factors that control the development and distribution of tectonic fractures were discussed by combining statistical and experimental analyses. Results indicate that natural fractures in the Feixianguan Formation can be genetically classified into tectonic and diagenetic fractures. Specifically, tectonic fractures include shear fractures and tensile fractures, in which the former are predominant. In the Feixianguan carbonates, tectonic shear fractures are mainly developed in the NE-SW and near E-W strikes, with dip angles mostly ranging from 30 to 70°. The majority of shear fractures appear on a small scale and have good effectiveness. The fracture heights and apertures are commonly less than 50 cm and 25 μm, respectively, and unfilled fractures account for more than half. The distribution and development of tectonic fractures are mainly controlled by lithology, mechanical stratigraphy, reservoir physical properties, diagenetic cementation, and faults. In the Feixianguan carbonates, tectonic fractures are more developed in crystalline dolomite. With the increasing thickness of mechanical stratigraphy, the fracture density decreases and the scale increases. The presence of early dissolution pores can prevent the formation of later tectonic fractures. Tectonic fractures in the NNW-SSE and near N-S strikes generally possess poor effectiveness due to multiple cementations after their formation. In the vicinity of faults, tectonic fractures generally stretch subparallel to the extension direction of the fault, and the development degree of fractures close to major faults is higher.

Simulation of tectonic stress field and prediction of tectonic fracture distribution in Longmaxi Formation in Lintanchang area of eastern Sichuan Basin

Shale is a low-porosity and low-permeability reservoir, and structural fractures are the main controlling factor for the migration and accumulation of shale gas. Moreover, tectonic fractures are controlled by the paleo-tectonic stress field. In this paper, taking the Longmaxi Formation of the Lintanchang area as an example, the finite element numerical simulation technology is used to analyze the distribution law of the paleo-tectonic stress field, and further, the fracture development areas under the superposition of two periods of tectonic stress are predicted using seismic, rock mechanics, and field data. The results show that the tectonic fractures developed in the Lintanchang area are mainly EW- and NNW-striking conjugate shear fractures formed in the Mid-Yanshanian period, followed by the NWW- and SWW-striking conjugate shear fractures formed in the late Yanshanian period. The distribution of tectonic fractures is affected by faults, folds, rock physical parameters and tectonic stresses. It is found that the comprehensive fracture coefficients of the anticline core and fault areas are both greater than 1.1, which are the areas with the most developed structural fractures, and these areas have poor shale gas preservation conditions. However, the comprehensive fracture coefficients of the western flanks of the anticline and the eastern and western dipping ends are between 1.0 and 1.1, which are areas with better shale gas preservation conditions. In addition, the development degree of tectonic fractures in the east and northwest areas of the Lintanchang anticline is lower than that in other areas. The comprehensive fracture coefficients of shale in these areas are between 0.9 and 1.0. The shale is in a state of “breaking without cracking”, and shale gas can be well preserved.

Simulation of multi-period tectonic stress fields and distribution prediction of tectonic fractures in tight gas reservoirs: A case study of the Tianhuan Depression in western Ordos Basin, China

Abstract Hydraulic fracturing technology, which is emerging in low- or ultralow-permeability oil and gas and tight gas reservoirs, has become a key technology for improving the development efficiency and economic benefit of unconventional gas reservoirs. The success rate of hydraulic fracturing is closely related to the development and distribution of natural fractures. Data obtained from outcrops, cores, thin sections and image logging were used to determine the developmental characteristics of tectonic fractures in the study area to obtain a quantitative forecast of the distribution of gas reservoir fractures in the Tianhuan Depression. With the aid of burial history analysis, geologic interpretation, seismic inversion, logging evaluation, rock mechanics and acoustic emission tests, 3D geomechanical models were established using the finite element method in Tianhuan Depression to simulate the paleotectonic stress fields during Indosinian, Yanshanian and Himalayan periods. The effects of different rock mechanics parameters on the development and distribution of tectonic fractures were identified. A fracture density model was established to determine the quantitative development of tectonic fractures in the upper He8 Member during the production of multi-period tectonic stress fields. The validity of the fracture density model was verified by the fracture statistics of drill core density and gas well productivity tests. Favorable areas for hydraulic fracturing were also determined. Simulation results indicate that the maximum and minimum principal stresses and the maximum shear stress during the Indosinian, Yanshanian and Himalayan periods are controlled by the distribution of the sand body. Rock mechanics parameters play important roles in the development of tectonic fractures in the sedimentary basin with less faults and folds. The 3D models of the multi-period tectonic stress fields and density calculation modelling are not only significant for tight gas sandstone reservoirs but also for predicting of other reservoir fractures.

Quantitative prediction of fracture distribution using geomechanical method within Kuqa Depression, Tarim Basin, NW China

Understanding and predicting the development and distribution of tectonic fractures in the super-deep tight sandstone reservoir are important for both gas exploration and exploitation activities in Kuqa Depression. We analyzed the characteristics of regional structural evolution and paleotectonic stress field setting. A reasonable geological model of the research area was built based on an interpretation of the geological structure, a test for rock mechanics, and experiment on acoustic emission. Thereafter, a three-dimensional paleotectonic stress field during the Late Himalayan movement was simulated by the finite element method. Composite rock failure criterion and geomechanical models between fracture density, aperture, strike and strain energy density were used to determine the quantitative development of fractures and predict zones that are prone to fracture development. Areas with well-developed tectonic fractures are mainly controlled by the tectonic stress field and elastic strain energy density, typically located in the fold limbs, fault zones and locations of changes in the orientation of fault. In turn, factors of faults, the lithology, depth and curvature control the development and distribution of tectonic fractures in the tight sandstone. The overall simulated results match well with core observation and FMI (Formation MicroScanner Image) results both in the whole geometry and fracture distribution. This evolutionary model of the structures present to us is a distinct and intuitive top-popup fold with low amplitude and relatively low-density fractures in the top, has only experienced pre-folding stage and strong folding stage, and has not yet been developed to vertical uplift stage.

Simulation of Paleotectonic Stress Fields and Distribution Prediction of Tectonic Fractures at the Hudi Coal Mine, Qinshui Basin

AbstractStudy on tectonic fractures based on the inversion of tectonic stress fields is an effective method. In this study, a geological model was set up based on geological data from the Hudi Coal Mine, Qinshui Basin, a mechanical model was established under the condition of rock mechanics and geostress, and the finite element method was used to simulate the paleotectonic stress field. Based on the Griffith and Mohr‐Coulomb criterion, the distribution of tectonic fractures in the Shanxi Formation during the Indosinian, Yanshanian, and Himalayan period can be predicted with the index of comprehensive rupture rate. The results show that the acting force of the Pacific Plate and the India Plate to the North China Plate formed the direction of principal stress is N‐S, NW ‐ SE, and NE ‐ SW, respectively, in different periods in the study area. Changes in the direction and strength of the acting force led to the regional gradients of tectonic stress magnitude, which resulted in an asymmetrical distribution state of the stress conditions in different periods. It is suggested that the low‐stress areas are mainly located in the fault zones and extend along the direction of the fault zones. Furthermore, the high‐stress areas are located in the junction of fold belts and the binding site of multiple folds. The development of tectonic fractures was affected by the distribution of stress intensity and the tectonic position of folds and faults, which resulted in some developed areas with level I and II. There are obvious differences in the development of tectonic fractures in the fold and fault zones and the anticline and syncline structure at the same fold zones. The tectonic fractures of the Shanxi Formation during the Himalayan period are more developed than those during the Indosinian and Yanshanian period due to the superposition of the late tectonic movement to the early tectonic movement and the differences in the magnitude and direction of stress intensity.

Fracture characteristics and their effects on hydrocarbon migration and accumulation in tight volcanic reservoirs: A case study of the Xujiaweizi fault depression, Songliao Basin, China

The Xujiaweizi fault depression is located in the northern part of the Songliao Basin, China. The Yingcheng Formation of the Xujiaweizi fault depression is a fractured tight volcanic reservoir. Many primary pores exist in the tight volcanic reservoirs of the Yingcheng Formation, but their connectivity is very poor. The degree of development of tectonic fractures determines the reservoir quality and the probability of hydrocarbon accumulation. To elucidate the fracture characteristics and their effects on hydrocarbon migration and accumulation, we analyze the fracture genetic types, characteristics, and controlling factors using data from cores, image logs, and thin sections. Then, we evaluate the matching relationship between tectonic fractures and hydrocarbon migration and accumulation by combining the evolution of the source rocks, analysis of the gas-source fault activity period and evolution of the cap rock sealing ability. We find two types of fractures developed in tight volcanic rocks: primary fractures and secondary fractures. Primary fractures mainly include cooling contraction fractures and cryptoexplosive fractures. Secondary fractures could be further divided into tectonic fractures, dissolution fractures, and weathering fractures. Among them, tectonic fractures are dominant. The distribution of tectonic fractures is controlled by lithology, lithofacies, faults, rock anisotropy, and an unconformity. Tectonic fractures are mainly formed in three phases. The time when the second phase of tectonic fractures formed (the Late Quantou-Qingshankou period) coincided with the peak hydrocarbon generation of the source rocks of the Shahezi Formation. Also at that time, the gas-source faults were active and the cap rock had a good top-seal capacity. Thus, the Late Quantou-Qingshankou period was the main period of natural gas accumulation.

Prediction of tectonic fractures in low permeability sandstone reservoirs: A case study of the Es3m reservoir in the Block Shishen 100 and adjacent regions, Dongying Depression

Tectonic fractures are important reservoir spaces for storage of hydrocarbons in low permeability sandstone reservoirs and can significantly improve the permeability; therefore, understanding and predicting their location and intensity in reservoirs are of extreme importance for both the exploration and exploitation planning activities. In the present study, the Early Himalayan Dongying period paleotectonic stress field, the period of time when the majority of tectonic fractures generated in the Dongying Depression, Bohai Bay Basin, China, was simulated and investigated with a three dimensional finite element (3D FE) model. Estimation of the Comprehensive Rupture Rate (CRR) and the relationship between the measured tectonic fracture densities and CRRs were undertaken to quantitatively predict the development and distribution of tectonic fractures in the Es3m low permeability sandstone reservoir. The results indicated that well developed tectonic fractures were located in regions within and between fault zones, near fault tips, and the eastern parts of Block Shishen 100 and adjacent regions. Fault activities were critical to the development and distribution of tectonic fractures in the Es3m reservoir of Block Shishen 100 and adjacent regions. In addition, abnormal high fluid pressures in the Es3m reservoir can promote the development of tectonic fractures.

Numerical study of multi-period palaeotectonic stress fields in Lower Cambrian shale reservoirs and the prediction of fractures distribution: A case study of the Niutitang Formation in Feng'gang No. 3 block, South China

Fractures not only control the distribution of oil and gas reservoirs, but also are key points in the research of oil and gas reservoir development programmes. The tectonic fractures in the Lower Cambrian shale reservoirs in the Feng'gang No. 3 block are effective reservoir spaces for hydrocarbon accumulation, and these fractures are controlled by palaeotectonic stress fields. Therefore, quantitatively predicting the development and distribution of tectonic fractures in the Lower Cambrian shale reservoir is important for the exploration and exploitation of shale gas in the Feng'gang No. 3 block. In the present study, a reasonable geological, mechanical and mathematical model of the study area was established based on the faults systems interpreted from seismic data, fracture characteristics from drilling data, uniaxial and triaxial compression tests and experiments on the acoustic emissions (AE) of rocks. Then, a three-dimensional (3-D) finite element method is applied to simulate the palaeotectonic stress field with the superposition of the Yanshan and Himalayan movements and used to predict the fracture distribution. The simulation results indicate that the maximum principal stress value within the study area ranged from 269.97 MPa to 281.18 MPa, the minimum principal stress ranged from 58.29 MPa to 79.64 MPa, and the shear stress value ranged from 91.05 MPa to 106.21 MPa. The palaeotectonic stress field is controlled by the fault zone locations. The fracture development zones are mainly controlled by the tectonic stress fields and are located around the faults, at the end of the fault zones, at the inflection point and at the intersection of the fault zones.

Tectonic Fractures in the Lower Cretaceous Xiagou Formation of Qingxi Oilfield, Jiuxi Basin, NW China. Part two: Numerical simulation of tectonic stress field and prediction of tectonic fractures

In the Xiagou low permeability reservoir, tectonic fractures are important reservoir spaces for storage of hydrocarbon and can significantly improve the permeability; therefore, understanding and predicting the development and distribution of tectonic fractures in the Xiagou reservoir are important for both petroleum exploration and exploitation activities in the Qingxi Oilfield. In the present study, the Himalayan paleotectonic stress field, the period of time when the majority of unfilled tectonic fractures generated in the Xiagou Formation of Qingxi Oilfield, was simulated with a three dimensional (3D) finite element (FE) model. Estimations of rock failure criteria (RFC) and comprehensive rupture rate (CRR) were undertaken to quantitatively determine the development and distribution of tectonic fractures in the Xiagou reservoir. Horizontally, areas with well-developed tectonic fractures were primarily located in fault zones, regions among faults, around Well G107 and with changes in the orientation of faults. Vertically, the K1g3 layer showed a relative higher CRR, indicating that it was highly fractured. Factors of faults and the lithology controlled the development and distribution of tectonic fractures in the Xiagou reservoir of Qingxi Oilfield. Abnormal high fluid pressures in the Xiagou Formation can promote the development of fractures in reservoirs and the transformation from shear fractures to tensile fractures under certain conditions.