The Marathon Petroleum Corporation is one of the largest refiners, marketers and transporters of petroleum products in the U.S. We provided technical services for the development of a hard-rock liquid-butane storage cavern, with a capacity of one million barrels, to serve the Marathon refinery in Catlettsburg, Kentucky. It is the first shale cavern constructed in the U.S. since 1984.

We were initially retained to conduct site screenings and prepare geotechnical feasibility studies for cavern development. The work included drilling of four new exploratory core holes in the cavern vicinity. Based on an array of core samples, we developed a geological profile for the cavern and designed surface and subsurface facilities. When construction began, we managed the drilling of an 8-foot-diameter main shaft and two 36-inch-diameter ventilation/pump shafts, while a third-party contractor was responsible for cavern excavation. Work on the project was temporarily suspended after approximately 225,000 oil barrels (bbl) of volume had been excavated. When it resumed, we were retained under an at-risk, lump-sum turnkey contract to complete the cavern excavation, conversion, testing and commissioning.

To address risks related to the contract takeover, operations and maintenance of in-place mining and hoisting equipment, and maintenance of the required design pressure, we developed a comprehensive risk assessment, management and mitigation program that included preparing a risk register to identify key risks, as well as various risk management and mitigation measures. The risk register and management and mitigation plans were used to guide contract negotiations, and were subsequently used in the execution of the work.

Risk management activities included engaging a team of mechanics to inspect and operate the owner’s underground equipment and develop a plan and cost estimate for restoring the equipment to full serviceability, conducting a thorough geotechnical inspection of the existing excavation and developing a remedial plan, and resealing and pressure testing the existing excavation to ensure the cavern’s containment integrity and reduce the risk of final pressure-test failure. The storage cavern was delivered in 2012 under budget and seven months ahead of schedule.