Abstract
Insufficient borehole pressure integrity (BHPI) is a major drilling challenge in deep, high-temperature, high-pressure (HTHP) wells in California and other areas. Shale and sandstone formations with low BHPI may be weakened by leaking faults/ fractures or poor rock properties, causing lost returns with mud weights close to pore pressures. Drilling through depleted or low pore pressure formations with some probability of drilling into higher pressured zones in the same hole section compounds the severity of this challenge in the Temblor formation in Kern County, California.
This challenge was solved by an innovative treatment applied in the Berkley East Lost Hills No. 1 well. Compared to conventional methods, it increased leakoff test (LOT) and formation-integrity test (FIT) pressures to incremental values higher than those typically seen in the industry. Increasing BHPI allowed an additional 960 ft to be drilled before a 7-in. liner was set, and the well was drilled to 19,724 ft. This depth met the objective of the well (to obtain full penetration through the objective sands) and allowed the subsequent discovery of a pay zone. If the new treatment to increase the LOT had not been used, the 7-in. liner would have been set early, and it is unlikely that the discovery zone would have been penetrated.
Preventing skin and formation damage in potential zones of interest while treating weak points was another major concern heightened by a wide range of pore pressures. This paper discusses a theoretical mechanism to help explain how the treatment rapidly and substantially increases pressure integrity across both sand and shale formations. Minor penetrations in high and low-permeability sandstone-core tests help explain why the treatment system minimizes or prevents skin damage. Skin damage in the zones of interest may be prevented or minimized by BHPI treatments that only enter leaking fractures or faults.
Further development and deployment of BHPI treatment technology promises a step-change in industry practice to optimize well plans with lower cost programs for drilling fluids, casing design, cementing, and completion equipment. Optimized well designs should reduce both drilling days and flat time by allowing operators to drill smaller-diameter holes while using fewer casing strings to achieve the same production-string dimensions.
