Potter Drilling, Inc. was founded in 2004 by father-and-son team Bob and Jared Potter. The ultimate goal of the company is to develop hard-rock drilling technologies that can realize engineered geothermal systems (EGS) and dramatically expand the availability of geothermal power. Potter Drilling’s patented and patent-pending drilling and ho
Improving Thermal Spallation Drilling
Unlike many other renewable sources of power, geothermal resources provide a virtually constant supply of base-load energy without the need for additional power storage infrastructure or modifications to the existing power grid. Conservative estimates of geothermal resources in the United States suggest that sufficient recoverable geothermal energy exists to supply the country’s needs for several thousand years. However, the adoption of geothermal energy has been limited by high capital costs and economic risks. Chief among costs are drilling expenses, which account for as much as 60% of the total capital investment in a geothermal well. Typically located in hard rocks that present significant challenges to traditional drilling technologies, geothermal wells often entail slow drilling rates and increased equipment wear, causing further delays as worn and damaged drill bits are replaced.
Potter Drilling’s thermal spallation drilling and geothermal well enhancement technologies have the potential to make renewable geothermal energy production competitive with other energy resources by reducing drilling costs, improving well performance, and reducing economic risk. Potter Drilling is also applying its experience in thermal rock reduction to thermo-chemical and thermo-mechanical drilling and hole-opening systems, which could also have application in oil, gas, and other energy-related fields.
Potter Drilling uses thermal spallation drilling, a no-contact method of rock reduction, to excavate hard rock in the process described to the right. By aiming a jet of superheated fluid at the rock, spalls (small pieces of rock) are ejected from the surface in the process shown to the right. The jet can be controlled to drill deeper into rocks or aimed radially from the instrument to create larger cavities or improve the hydrodynamic performance of the borehole.
Lawrence Livermore National Laboratory, in collaboration with Potter Drilling, has developed computational methods for simulating Thermal Spallation Drilling at the grain scale. These previously developed models were combined with Livermore’s GEODYN code and PSUADE code for multidimensional parametric analysis and optimization, and the combined codes are used through the HPC Innovation Center to conduct benchmark simulations to validate large-scale spallation models for the industrial design optimization of Potter Drilling’s thermal rock reduction technologies.
This information will be pulled together into a tool that Potter Drilling can use to characterize rock systems to optimize drilling techniques and extrapolate to depths and conditions not feasibly explored with field tests. The results from these simulations will allow the engineering of drilling systems to overcome current challenges and produce faster designs evolutions.
Over 7,000 two-dimensional simulations- each using 72 computer processors-investigated borehole conditions including drilling fluid temperature, lithostatic and hydrostatic pressure, microstructural properties including grain-shape and size distribution, and thermal and mechanical properties to evaluate their effects on rock reduction over ranges of interest.
Of the 22 model parameters investigated, the factors listed below were found to be the most crucial to determining the extent of damage and spall size. To further understand their effects, 50 three-dimensional simulations – each using 1,020 computer processors – were completed. An example of three-dimensional simulation is shown below.
Rock parameters crucial in determining material response to Thermal Spallation Drilling:
- The difference in fluid jet and host rock temperature,
- Lithostatic pressure,
- Hydrostatic pressure,
- Grain interface strength, and
- Mineral volume fraction.
The results of this project will provide Potter Drilling with direct simulation data on types of rocks best suited for Thermal Spallation Drilling and the conditions under which they are most susceptible. It will also yield benchmark parameters to validate larger-scale models of Thermal Spallation Drilling at temperatures and pressures relevant to geothermal well field conditions. These borehole-scale models will ultimately be employed in system-scale simulations capable of implementation on a desktop computer or small computer cluster system that will be used for industrial design optimization of Thermal Spallation and thermo-mechanical drilling.
Prior to the hpc4energy incubator
Potter Drilling’s tool and system development has relied on an iterative design–optimization cycle, burdened by long cycle times and high costs, with little means to optimize or predict performance outside of test conditions. Development is further complicated by a lack of understanding of the phenomena of thermal spallation, including the effects of rock composition, grain size, grain size distribution, macroscopic characteristics (Poisson ratio, heat capacity, and thermal conductivity) and microscopic properties (flaw distribution and intergranular strength). Prior to the collaboration in the hpc4energy incubator, Potter Drilling ran experiments of 15 field trials with thirty different design and process changes.