A NEW MODELING OF CBM WELLBORE INTEGRITY BASED ON GEOLOGY, GEOPHYSICS, RESERVOIRS, DRDLLBSfG AND PRODUCTION ENGINEERING

摘要

Unlike conventional sandstone reservoirs, where the gas is found in a free state within the pore structure of the rock, in CBM the methane gas is adsorbed onto the internal structure of the coal, which allows a significant amount of gas to be stored in the coal rock. CBM now becomes more attractive for exploration and exploitation because of higher gas demands around the world. A conventional CBM production method can only be economical in coal seams with good porosity, permeability and natural fractures. It is a common procedure to conduct a wellbore integrity study in oil and gas well planning. The study will incorporate geologic, geophysics and reservoir properties to establish the target and design of drilling and well completion. In terms of CBM production, while there are similarities between oil and gas reservoirsand CBM, there are also differences that affect the planning and design principal of a CBM well and field. Those differences will be mapped in a wellbore integrity aspect in CBM well construction, which distinguishes CBM from oil and gas design. Developments in directional, horizontal and multilateral wells have delivered new breakthroughs to replace vertical drilling systems in CBM drilling, to optimize gas production. To minimize risks and costs in CBM drilling, an analytical comparison study of those drilling methods is needed. This study presents a new modeling of wellbore integrity and its influence on CBM well construction and design, which provides an optimum planning strategy for CBM drilling engineering and well completion.