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HPHT drilling operations in exploratory areas with high differential pore pressures are an ongoing challenge. One operator used an unconventional drilling fluid formulation to successfully drill their highest overbalanced well to date. The high-pressure, high-temperature (HPHT) section exhibited pore pressures up to 14,000 psi with 310°F bottomhole temperature. The challenge was further compounded by the very high overbalance pressure − approximately 6,800 psi observed while drilling with an 18.4-lb/gal drilling fluid.
In the deeper section, where wellbore pressure control was critical with approximately a 1.5-lb/gal drilling window, the HPHT drilling fluid formulation and rheology were optimized to minimize the equivalent circulating density. To minimize risk of wellbore losses and differential sticking, a HPHT low-invasion fluid system with FLC 2000 technology was selected to provide wellbore shielding. Monitoring in the lab and with unconventional test equipment in the field provided further fine tuning of the mud formulation.
The challenging 8½-in. HPHT hole section was successfully drilled with no issues with mud losses, drag during tripping, or differential sticking. The superior HPHT drilling fluid system enabled the well to meet its objectives of producing from shallow intervals while further appraising the deeper 8½-in. HPHT section.