Pushing the Envelope of HT Drilling Fluids: Development and Field Applications of a Novel Non-Aqueous Drilling Fluid in the Gulf of Thailand

Abstract

Abstract Typical wells in the Gulf of Thailand are drilled using a slim-hole design that requires 6⅛-in. hole for their reservoir interval. The slim and highly deviated well geometry, potential of high acid gas contamination, and high-temperature environment requires a well-engineered non-aqueous drilling fluid (NAF) to meet the overall well objectives. These conditions always place severe limitations on the drilling fluids design and often lead to failures in openhole wireline logging operations, which is the most important well objective. The key fluid properties to ensure the success of wireline logging operations under this high temperature are high-temperature, high-pressure (HTHP) filtration control, filtercake quality, and thermal stability of the drilling fluid under extreme static condition. Selected emulsifier and HTHP filtration control agents work synergistically in providing excellent hole condition which allows the hole to be fully logged and evaluated. Clear benchmarks were set and monitored in all the field applications: (1) Successful wireline logging operation; (2) Variation of mud weight after static condition; (3) Variation of mud weight compared to formation tester data point. This paper details the design, development, and field applications of an ultra-high-temperature NAF used for drilling deep and hot wells in the Gulf of Thailand. In addition, the extensive laboratory work required to optimize the formulation for extreme high temperatures, the lessons learned, and the critical engineering guidelines for running a NAF in such harsh conditions will be described.