Research and application of water-based drilling fluid technology of Sichuan Changning block shale-gas horizontal well

Changning Longmaxi shale mineral components are mainly composed of quartz, calcite and clay mineral, and it belongs to brittle and water sensitive formation. In order to satisfy the needs that water base drilling fluid can drill in the long horizontal section of shale, and also the underground complex situation such as well-bore instability and sidewall collapse can not happen, through a large number of laboratory studies, the drilling fluid system was formulated with a hydrophilically inhibitive agent CQ-SIA and a high performance lubricant CQ-LSA as the core additive of the formulation, which was suited to drilling in shale formation. The experimental results showed that the water base drilling fluid had excellent inhibition ability and the rolling recovery rate was 97.6%; after 48 hour static at 100 ℃, the phenomenon of barite settlement did not happen, and the rheological property was stability; the system could resist the 30% plus amount of debris pollution. The field application showed that the drilling fluid had stable performance, good lubrication performance, and strong inhibition ability. It could ensure the smooth drilling, electrical measurement, drifting and running casing construction operations. The system could meet the need of Changning shale gas well drilling.