Study on Fracture Characteristics and Controlling Factors of Tight Sandstone Reservoir: A Case Study on the Huagang Formation in the Xihu Depression, East China Sea Shelf Basin, China

Abstract

Natural fractures are not only the key to affect the natural productivity of tight sandstone reservoirs but also one of the important factors to control the fracturing effect. If the local strata are affected by multistage tectonic movement and diagenesis, it will lead to the complexity of fracture types and characteristics, which makes it difficult to accurately identify natural fractures, thus, seriously affect the development of fractured reservoirs and the fracturing effect. In this paper, the macroscopic fractures were studied by combining core, conventional logging, imaging logging, petrophysical logging, logging, drilling, and gas test data. The microscopic fractures were analyzed by casting thin sections and scanning electron microscopy and cathodoluminescence. The effect of fractures on hydrocarbon migration was analyzed by fluid inclusions in fractures. The core can be used to visually study the opening fracture, but when the color of the filling inside the fracture is similar to the surrounding, the filling fracture is not easy to be found. Imaging logging has high identification accuracy for filling fractures, but it can hardly be used as a means of identifying high-angle opening fractures. The opening fracture zone in the noncoring section can be studied by conventional logging, mud logging, drilling, and rock mechanical parameter. The macroscopic structural fractures are obviously directional, which is controlled by the tectonic stress field. The occurrence and density of macroscopic structural fractures are controlled by buried depth, lithology, rock thickness, sedimentary facies, distance from the fault, and structural location. The opening fractures are all of high angle, indicating that the inclination angle is an important factor affecting the filling degree of fractures. The direction of intragranular fractures is chaotic, which is affected by the mechanical weak surface of the mineral particles, particle morphology, and particle contact relationship and stress. Effective fractures provide channels for the migration of oil and gas and acidic fluids in the historical period, which promote the occurrence of hydrocarbon accumulation and dissolution.

Fine-Grained Lithofacies Types and Sedimentary Model of the Upper Permian Longtan Formation Coal Measures in the Western Guizhou Region, South China

“…A lithofacies assemblage refers to a set of symbiotic lithofacies that are closely related in terms of their genesis and sedimentary environment. , A lithofacies assemblage reflects a certain sedimentary environment and its sedimentary processes and is a product of a single sedimentary event or a continuous evolution of a specific environment. Lithofacies assemblages represent specific environmental conditions during a particular period, such as climate, hydrodynamics, and sediment sources, and can reflect the regular evolution of each environmental condition. , Based on observations of the core samples and thin sections in the study area and combined with the analysis of measurement and logging data, the six typical lithofacies assemblages are believed to have mainly developed in the Longtan Formation in western Guizhou. Typical core segments and field sections were selected to describe the developmental patterns and petrological characteristics of the lithofacies in the six lithofacies assemblages (Table ).…”

“…Lithofacies assemblages represent specific environmental conditions during a particular period, such as climate, hydrodynamics, and sediment sources, and can reflect the regular evolution of each environmental condition. 78 , 79 Based on observations of the core samples and thin sections in the study area and combined with the analysis of measurement and logging data, the six typical lithofacies assemblages are believed to have mainly developed in the Longtan Formation in western Guizhou. Typical core segments and field sections were selected to describe the developmental patterns and petrological characteristics of the lithofacies in the six lithofacies assemblages ( Table 4 ).…”

Analysis of Multi-Fracture Extension Pattern of Horizontal Wells in Shale Reservoirs under Natural Fracture Perturbation

“…In the study of hydraulic fracturing processes, the fracture initiation and propagation are simulated using cohesive elastic-plastic elements based on the principles of fracture mechanics. Figure 1 shows the criteria for damage assessment in cohesive elastic-plastic elements [13]. Criterion for cohesive element fracture initiation:…”

Effect of saline sedimentary environment on pore throats of shale

“…Fractures are a key factor in unconventional reservoir development (Zhao et al, 2021). By analyzing the characteristics of shale storage, it is believed that the shale storage space mainly has micropores (organic pores, intercrystal pores, and intergrain pores) and microcracks…”