No abstract

The Songhe mine field located in western Guizhou Province of China is the most typical region of multiple coal seam development. However, the coalbed methane development practices of commingled drainage in recent years have been proved to be less ideal. In this work, on the basis of dividing gas system, the correlations between geological and engineering factors and gas production data were studied to determine the controlling factors of coalbed methane well productivity. The results indicated that the gas production had a positive correlation with cumulative thickness and gas content of fractured coal seams overall. However, the large cumulative thickness is generally resulted from the increase of coal seam number, and thus increases the reservoir heterogeneity and interlayer difference. The coalbed methane well productivity performance for this type region was a result of the strong interaction of cumulative thickness, burial depth, gas content, permeability, and reservoir pressure of fractured coal seam. However, the interlayer interference was the most direct factors restricting the productivity of commingle drainage by affecting the speed of dewatering and lowering of pressure and gas desorption time of gas-bearing systems. Additionally, the correlations between gas production and interlayer difference and interference were quantitatively analyzed, and the results showed that the wells with large interlayer difference and interference tend to have a poor productivity performance. As a result, the drainage method was particularly an important factor controlling the well productivity for multiple coalbed methane systems, because a proper combination of gas-bearing system and drainage and dewatering sequence are the keys to decrease the interlayer interference. Finally, the commingled

The Cenozoic North Altyn Fault (NAF) is a major splay of the Altyn Tagh Fault along the northwestern margin of the Tibetan Plateau, but its role in the development of this plateau margin in response to the India‐Eurasia collision is highly debated. Here, we investigate fault geometry, kinematics, and shortening magnitude along the westernmost 120 km of the NAF. Seismic surveys reveal minimal Cenozoic shortening in the subsurface of the Southeast Tarim Basin and support for large‐scale (>120 km) left slip on the NAF. Based on the satellite imagery, two new faults are identified to define the northern boundary of the NAF system, which together with the NAF to the south constitute a narrow transpressional shear zone comprised of three basement‐cored, fault‐bound slivers. Fission track data and thermal modeling indicate that the NAF zone experienced broad reburial during early Cenozoic that was locally interrupted by ∼40 to 35 Ma exhumation proximal to the NAF, followed by widespread but heterogeneous exhumation since ∼17 to 15 Ma associated with ∼9 to 11 km of total shortening across the NAF system via thick‐skinned faulting. We conclude that the NAF initiated as a left‐slip fault at ∼40 to 35 Ma and then became transpressional at ∼17 to 15 Ma during the middle‐Miocene reorganization of the Altyn Tagh Fault system. We find no evidence to support prior inferences of large‐scale (∼100 km) underthrusting of the Tarim Basin beneath the Tibetan Plateau along the NAF.