Modeling a Deep Coaxial Closed-Loop Vacuum Insulated Tubing (VIT) Completion in a Geothermal Research Test Well Using FEFLOW

摘要

ABSTRACT: An innovative geothermal research test well was successfully drilled and completed in a drilling test facility in Navasota, Texas in 2020. This vertical test well reached 11,518 ft (3510.7 m) total depth and set a 6-inch casing to 11,503 ft (3506.1 m) with a DTS/DAS fiber optic cable permanently installed on the outer diameter of the 6-inch casing and cemented in place. At the time, a vacuum-insulated-tubing (VIT) completion was installed from surface to ∼11,369 ft (3465.3 m) to pilot-test a deep coaxial closed-loop geothermal system. The test well was flowing down annulus and up tubing with filtered freshwater being the working fluid. Selected flow rates were 150 gal/min (gpm), 75 gpm and 37.5 gpm. A three-dimensional (3D) FEFLOW finite-element borehole heat exchanger (BHE) model was developed to model the impact of different key parameters such as formation and cement thermal conductivities, flow rates and inlet temperature after the model is calibrated against the field data. The model can be used to simulate energy output and heat production forecast for similar geothermal completions such as BHEs and borehole thermal energy storage (BTES). 1. INTRODUCTION OF THE TEST RIGS AND THE TEST FACILITY The NOV STC (Springett Technology Center) test facility is located in Navasota in Grimes County, Texas. The geothermal test well was drilled with the automated Ideal Prime 1 drilling rig (1500 hp) and completed with a 5C mobile completion rig (200 kips or 100 US tons static hook load capacity). The Prime 1 rig consists of an automated Iron Roughneck (ST-100) and 3 permanently installed Robots for automated pipe handling during tripping. The first floor Robot (L1) handles pipe tailing between the well center and the setback area as well as picking up a single joint from the Pipecat. The second floor Robot (L2) handles the ancillary work which includes operating the mud bucket and a combo of the doping head and stabbing guide. the third robot is located above the finger board to handle the top of the pipe stands between the top drive elevator and the finger traps. At the time of this paper being written, the drill cabin has been removed from the drill floor to the ground level for over nine months with non-interrupted rig operations and testing.