Environmental-friendly drilling fluid system in offshore natural gas hydrate formations

Abstract

There are abundant natural gas hydrate resources in offshore. However, the development of drilling fluid system is restricted by low ambient temperature, special formation conditions of weak cementation and high environmental protection requirements of marine discharge. In this paper, a new environmental-friendly drilling fluid system in offshore gas hydrate formations has been developed by optimizing the additives. The comprehensive evaluation shows that the freezing point of the drilling fluid can reach -10 °C, and it still has good rheological properties at 4 °C. The apparent viscosity ratio of the drilling fluid is less than 1.3, and the fluid filtration is only 4 mL. With good shale hydration inhibition, it can significantly reduce the swelling ratio and increase the cuttings dispersion recovery radio. There is no hydrate formation in drilling fluid for 24 hours at 4 °C and 10 MPa simulated conditions, which shows a good ability to inhibit gas hydrate formation. At the same time, compared with the experimental fluid without hydrate decomposition inhibitor, the drilling fluid can delay hydrate decomposition. In addition, the drilling fluid has good environmental protection performance, which can meet the requirements of high environmental protection in offshore.