Study on a High Temperature High Density Drilling Fluid Used on the Well LOFIN-2,Indonesia

Well Lofin-2, a deepest onshore well drilled in Indonesia, is a key exploratory well deployed on the Seran Island, east Indonesia, with vertical depth of 5861 m. The highest temperature of the well is between 150 ℃ and 180 ℃, and a mud of 2.10–2.16 g/cm³ has to be used to balance the formation pressures. Drilling challenges include fractured shales, high pressure saltwater zones, which are the causes of induced mud losses and formation water invasion, and silty mudstones, which are the easy to disperse into drilling fluid to make the mud rheology uncontrollable worse. A drilling fluid was formulated to deal with these problems. Some high temperature drilling fluid additives were selected to render the drilling fluid good stability at elevated temperatures. The water base drilling fluid formulated is able to work normally at temperatures up to 180 ℃ and has densities adjustable between 2.10 g/cm³ and 2.16 g/cm³. Field application of this drilling fluid showed that it had stable properties which were easy to maintain. The well was successfully drilled with no big troubles. The use of this drilling fluid has provided a choice of using HTHP drilling fluid in this block.