Characteristics of Reservoir Fractures in Amu Darya Right Bank and the Significance in Petroleum Geology

Studies show that carbonates in the central area of Block B on the Amu Darya Right Bank Gas Exploration and Development Project (hereinafter called Amu Darya Right Bank) are subjected to multistage regional tectonic activities under the tectonic structure background of stable subsidence. Fractures are well developed in reservoirs, combined with matrix pores in an extremely complex pattern, and characterized by strong randomness, great mutation, and significant differences in terms of spatial distribution. The characteristics and genesis of fractures in the study area are analyzed and the significance of such fractures in petroleum geology is discussed thoroughly. In this regard, microfracture effectiveness and storage capacity are obtained using imaging logging, CT scanning, nuclear magnetic resonance experiment, and seismic data. The obtained results show that ① structural fractures are the most developed reservoir fractures in the central area of Block B and are mostly semi-filled with calcite, quartz, and dolomite. ② It is found that microfractures in the central reverse fault were developed in three successions, including the late Yanshan period (I), the early Himalayan period (II), and the middle Himalayan period (III), respectively. The attitudes of the three stages are high-angle, bevel, and horizontal microfractures, respectively, which are distributed in a reticulated pattern and kept open for a long time with a low filling degree. These microfractures are the main channels for the produced water from the gas field. ③ Fractures are affected by multiple factors, including tectonic movement, ground stress, and sedimentary facies. ④ Fractures improve the physical properties of reservoirs and act as oil-gas migration pathways and communication channels with water bodies.