Reservoir protection and well completion technology for multi-branch horizontal wells in coalbed methane

Abstract

Coal reservoirs have characteristically low permeability and low pressure and are highly sensitive to damage during well completion. Therefore, systematic reservoir protection measures must be taken in the process of coalbed methane exploitation. However, in some areas such as the Qinshui basin, there is a contradiction between the sidewall stability of horizontal coalbed methane (CBM) wells and the protection of coal seams, which becomes the main technical bottleneck for the efficient development of CBM. Therefore, a double-pipe double-cycle rock carrying technology based on using a clean water drilling fluid is proposed, which can be applied to multi-branch horizontal wells of CBM, improve well completion efficiency and quality, realize reservoir protection, and increase single-well production. Field tests of this technology have been completed in wells ZS1P-5H and QS12P1H with satisfactory results. For example, the QS12P1H well was drilled with one main branch, 15 branches, and 33 pulse branches. The total depth of the well is 13,270 m, and the pure coal depth is 10,288 m. A single well of 10 km footage was realized without accidents, and the daily gas output was up to 10,000 m3.