LAUSR

Abstract This paper focusses on sequence stratigraphy of coal-bearing strata, coal petrography, coal chemistry, and the CH4 adsorption capacity of the Badaowan Formation in Santanghu Basin, China. The comprehensive coal characteristics of 12 coal samples were determined, coupled with maceral composition, proximate analysis, elemental analysis, reflectance (Ro), and high-pressure CH4 adsorption. The results indicated that maceral composition and chemical properties of coal were controlled by the sequence stratigraphic framework. During the TST, the content of vitrinite, the ratio of vitrinite to inertinite (V/I) and the content of carbon in coal increased gradually from bottom to top. While during HST, an opposite trend was observed. Furthermore, due to the intrusion of the lake water, the ash yield in the TST is higher than that in HST. The CH4 adsorption capacity is positively correlated with the content of vitrinite and V/I. There is a moderate positive correlation between fixed carbon contents and VLad. Ash content was strongly correlated to Langmuir volume under the air-dry basis, with increasing Ad associated with the reduction of the VLad. It was observed that the CH4 adsorption capacity generally gradually increased during the TST, and gradually decreased in the HST. Gas content also shows a similar change rule. CH4 adsorption capacity is functionally dependent on coal characteristics, which again are dependent on sequence stratigraphy and thus the coal-forming environment. The base level and cycles of the sequence establish a theoretical and practical framework for CBM extraction from low-rank coal reservoirs.