Geothermal Energy: A Novel Coiled Tubing Technology Transition

Abstract Coiled tubing has historically been a supporting technology deemed to interact closely with other technologies, given its versatility on equipment, pipe size and configuration, fluids used, tools conveyance, and interaction with the reservoir. Its applicability and value for hydrocarbon production have been vastly documented from drilling and completions to production enhancement and well abandonment. This paper describes a novel application, where an ultra-compact coiled tubing unit (UCCTU) was designed and built for shallow geothermal well drilling and reservoir/aquifer characterization, as part of a project to deliver geothermal energy in dense urban areas across the United States, decarbonizing buildings and reducing their dependance on the electrical grid. The UCCTU was designed and built in six months, where a conventional skid coiled tubing unit was customized for this shallow geothermal drilling application. Considering inner city weight, width, length, and height limitations, two complementing trucks were built. The equipment includes a control cabin, wet kit, coiled tubing reel, 2 3/8-in.coiled tubing with wired downhole telemetry, injector head, stripper, crane, and fluid pump, built considering the smallest footprint possible to ease access in streets and avenues. Engineering was performed to deliver the unit within the required time frame and evaluate modifications needed on the equipment to build this prototype, which would be used to drill wells and log during the process by means of the downhole telemetry. The unit went into field testing, running 2-3/8-in pipe with a downhole motor, drilling bit, and logging tools. At the time of writing this abstract, a total of four wells were drilled, which provided improvement opportunities: Unit design improvements Rig up and rig down process. Drilling and logging operational efficiencies. Location set up and layout. Aquifer characterization Several other details are included regarding shallow geothermal well design for direct heating and cooling applications, and tensile force analysis cases for certain coiled tubing configurations. This coiled tubing unit application is a disruptive step change on how the units can be designed for shallow well drilling, how they can be made more efficient, and most importantly, how can we transition oil & gas (O&G) proven technologies, such as coiled tubing, drilling, and logging, into geothermal energy production.