Increased global energy demand has forced the oil and gas industry to search for hydrocarbons in increasingly challenging locations such as high temperature, high pressure (HTHP) reservoirs. This paper presents the field performance of a new fit-for-purpose synthetic-based mud (SBM) used to drill an ultra-HTHP deep gas exploration well offshore Malaysia. The well was drilled to a total depth (TD) of 14, 380 ft (4, 383 m) and reached the highest recorded bottomhole temperature (BHT) of 488°F (253°C) in Southeast Asia. To overcome the anticipated drilling challenges in the extreme environments, the operator and service company collaborated to identify a thermally stable, high-density drilling fluid that met the operator's needs. The drilling fluid was formulated for a maximum density of 18 lb per gallon (ppg), but reached the Southeast Asia record of 19.1 ppg mud weight at TD. The use of dual weighting materials (barite and manganese tetraoxide) yielded lower plastic viscosity (PV) for the high-density mud, leading to improved hydraulics and lower equivalent circulating density (ECD). The drilling fluid encompassed excellent temperature stability with no weighting agent sag and no high-temperature gelation observed after remaining static for five days at BHT during wireline logging. In this respect, it eliminated the rig time spent for additional circulating or conditioning of drilling muds and fluid treatment cost. Moreover, the fluid also provided good wellbore stability with no non-productive time (NPT) from drilling fluid performance. Comparison of field data and laboratory results highlighted the benefits of competent drilling fluid design and testing. As a result of thorough planning and comprehensive laboratory testing, desirable drilling fluid properties were maintained despite extreme HTHP conditions, minimizing trips and operational costs.

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.

Global energy demand has driven the oil and gas industry to search for hydrocarbons in increasingly challenging reservoirs including those at high pressure and temperature (HPHT) such as found in the South Malay Basin of Malaysia. Competent well designs and enabling HPHT technologies such as advanced drilling fluid designs that are stable at HPHT conditions are critical to successful drilling and completion of these wells. This paper discusses the laboratory evaluation of potential HPHT drilling fluid designs considered for a deep gas exploration well in the Duyong Deep-1 field located in the South Malay basin of Malaysia expected to reach 455 °F (235 °C) and 13,683 psi. Laboratory testing encompassed fluid rheology, fluid loss, sag, electrical stability and chemical analysis before and after extended dynamic and static aging up to this temperature and pressure. Results were examined to identify strengths and weaknesses of the fluid designed. Improved-performance drilling fluid formulations underwent further pressure, temperature and hydraulic simulations to ensure adequate hydraulics and hole cleaning. As a result, suitable drilling fluid formulations for the ultra-HPHT gas well were successfully formulated with a maximum density of 18 ppg and thermal stability of 455 °F. The selected drilling mud design was stable and maintained desirable rheological properties including shear strength less than 200 lb/100 ft2 at static BHT at 16 and 48 hours.