Learnings From The High Temperature Water Based Mud Application in Offshore Sarawak

Abstract

A total of 5 production wells were planned in a gas field development project located in offshore Sarawak, Malaysia. The reservoir section of the field is comprised of two massive pinnacle carbonate structures, characterized by heterogeneous porosity and permeability, with high occurrence of vugs and faults. Severe to total loss circulation was expected while drilling this reservoir coupled with high temperature environment with prognosed bottomhole temperature (BHT) of 370°F. Considering the high risk of loss circulation, the drilling fluids strategy involved designing and testing of a high temperature tolerant Water Based Mud (WBM) system as a base case plan to drill the reservoir in the scenario of sustainable losses. The HT WBM system was designed using HT polymers for filtration control and viscosity. The fluid was stressed at 370°F and prepared at a density of 14.5 lb/gal (1.74 SG). The high density mud system prompted the requirement to control the rheology for improved ECD management while drilling the reservoir section. Other criterias for the fluids design were the ability to demonstrate low barite sagging tendencies at extended static aging time as well as improved HTHP filtration control. The final formulation was also subjected to a formation damage testing to evaluate the fluids impact towards reservoir impairment. The HT WBM system was a milestone for the operator as being the hottest HT WBM ever deployed in Malaysia operation. High geological uncertainties in the area led towards unexpected long shale exposure while drilling the reservoir section in both mainbore and sidetrack wells. While the mainhole was drilled successfully with the HT WBM system, the sidetracked well experienced significant reduction in the rate of penetration (ROP), suspected from bit balling despite having additional inhibition material in the system. The field observations, prompted additional learnings towards improvement of the HT WBM formulation as well as recommended lab testing considerations to further evaluate the performance of the mud system.