A lot of wells were drilled in the fractured granite formation of Indonesian Jabung Block without any oil and gas show. However, a discovery was made by the utilization of under-balanced MPD technology. This paper gives a description of the technological process of the MPD technology and equipment used in the exploratory well Basement-1#.
The 8-1/2in. hole section was drilled by application of MPD technology. The actual well depth is 8,269 ft, and the MPD hole section is between 4,993ft-8,269ft with footage of 3,276ft. The under-balanced drilling operation with managed pressure, tripping under managed pressure, displacement of weighted drilling fluid and overflow monitoring etc. had been successfully carried out during the MPD operation. Backpressure at wellhead was maintained in between 50-135psi. The abnormal downhole condition was monitored by little change of flow rate in and out of the well. Overflow was controlled in time and fluctuation of bottomhole pressure was decreased by use of accurate operation of the MPD equipment. A system of a synthetic based Gas-To-Liquid (GTL) drilling fluid was used to keep a low density as 7.4ppg since the formation pressure coefficient is around 1.04. The system kept good and stable performance with suspension and carrying capacity.
The overall MPD process was effective without any problems. No losses occur, and non-production time was reduced. Success ignition was not sooner than drilling 30ft into the basement. 57 times of successful ignition were done in 300hrs of MPD operation. The longest continuous ignition reached 75hrs out of total 240hrs of ignition. The maximum total hydrocarbon reached 36.3% and revealed good hydrocarbon shows.
Under-balanced managed pressure drilling could contribute to discovery of oil and gas reservoirs, make benefit to assessment of productivity of oil and gas wells. In addition, it increases rate of penetration, save overflow treatment time, and improve well control process.