Proven Expertise in Hard-Rock Caverns
This 1.4-million-barrel underground cavern for storage of butane was constructed in shale at a depth of 650 feet. We were engaged to provide engineering, procurement and construction management services on the project following our successful delivery of an earlier storage cavern project for the same client.
The cavern is located near the client’s refinery. The geology of the area is particularly suitable for pressurized storage of liquid petroleum products. The cavern uses a modified “room and pillar” design, with a series of lateral drifts separated by pillars to maintain structural integrity.
Site preparation occurred during a period of unusually heavy rain. Unconventional site equipment, including haul trucks, were used to keep the project on track. We subsequently managed the drilling program, preparing the way for breakout mining activities. Breakout mining consisted of six months of methodical hand excavation before larger equipment could be mobilized.
Once the larger mining equipment was mobilized, the production mining phase proceeded on an expedited basis. It included installation of a solid and durable roof support system with a minimum of 50 years of service life. This is a critical feature—it is not possible to enter the cavern to perform maintenance of the support system since the cavern is sealed in order to store product safely. Underground demobilization, cavern conversion for storage, and final pressure testing were the final phases of cavern development.
Innovative Features and Solutions
This cavern project set a North American record for simultaneous drilling of three shafts at a single location. Two eight-foot-diameter shafts were drilled—a service shaft for transporting people and equipment and a production shaft for removing excavated rock—along with a six-foot-diameter fresh air ventilation shaft. The simultaneous drilling saved approximately two months on the project schedule.
The cavern design also had to be adapted to respond to actual geological conditions encountered at the site. Extremely low temperatures during winter required special techniques, such as the use of heaters to keep the ground and rebar from freezing. A major challenge in mobilization and demobilization was moving the large mining equipment through a shaft with minimal clearance, which required detailed planning and careful execution. Despite these challenges, the project proceeded ahead of schedule and within the original budget.