CBM reservoir thickness affects production from horizontal wells

摘要

A stimulation study shows the importance of considering reservoir thickness when developing low-permeability coalbed methane (CBM) resources with a horizontal lateral. The study determined that when the thickness is less than a critical value, the well will produce less cumulative gas and decrease its commercial value. When the thickness exceeds the critical thickness, the productivity will not increase as reservoir thickness increases but will remain stable as thickness increases. At present, most coalbed methane reservoir developments in China use fractured vertical wells and herringbone horizontal wells. The cost of a fractured vertical well is low but these wells have a limited drainage area. Although common for developing hydrocarbon reservoirs, horizontal wells are much less common for CBM reservoirs. As the reservoir thickness increases, the recovery factor is lower because the gas will not desorb as efficiently as in thinner beds, but the cumulative gas produced is higher.