The oil and gas industry has made enormous strides in the development of fracturing technology since the late 1970s when fracturing first became a significant part of the industry. Multistage fracturing, proppants, microseismic fracture mapping and advanced fracturing fluids combined with horizontal drilling has allowed the recovery of oil and gas stored in very low permeability shales and sandstones. This has significantly extended the availability of these fossil fuels for energy production. A long period of low prices for oil and gas along with the concerns about CO2 emissions and global climate change has resulted in a return of interest in geothermal energy on the part of oil and gas and service companies. Can the technologies that made the shale revolution possible be applied to geothermal energy? This paper examines the similarities and differences between geothermal and oil and gas and suggest the areas where technologies developed for oil and gas can be applied to geothermal to reduce the cost and risk in producing geothermal heat and power. Early efforts to use stimulation technology in geothermal focused on high temperature rock at relatively shallow depths. Because the energy density of geothermal fluids produced in the temperature range where drilling tools, bits, instrumentation and completions were possible is low, very high flow rates are needed to make drilling for these resources economic. The initial focus in technology development for stimulation in geothermal was therefore on producing high flow rates using massive hydraulic fracturing methods. It was clear that in order to produce these high flow rates, large diameter completions with either open hole or hung perforated or slotted liners were needed to avoid high pressure drop that would result in loss of energy to pumping. While packers and other mechanical ways to isolate zones for fracturing were available for temperatures encountered in oil and gas, these devices failed regularly in geothermal stimulation efforts. Packers set in the open hole failed to hold or release or fractures grew around the packer without extending. Cement and perforate completions that would have made it possible to set packers against casing resulted in too high pressure drop as the fluid entered or exited the wellbore. Fracturing fluids clumped up or lost viscosity at lower geothermal temperatures and carbonized at high temperatures. Proppants dissolved or failed to stay in place in production wells due to the very high velocities of high temperature fluids. Horizontal drilling methods were expensive at high temperature and weren’t applicable to geothermal since these techniques are used to follow a thin sedimentary layer over long distances. The result was that most geothermal fracturing was done by bull heading cold water from the surface for extended periods to create a massive volume of fractured rock to get good heat exchange. Hydroshearing with self propping and thermal contraction of the rock kept fractures open. One primary exit point from a well deviated to be orthogonal to the direction that fractures would form created large complex fracture networks. However, flow rates were limited to 30-40 kg/s due to the lack of ability to create multistage fractures. Drilling for very high temperature rock, above the critical point for water, can increase the energy density for geothermal fluids and therefore improve the economics of geothermal energy development. What technology from unconventional oil and gas development can be applied now at these very high temperatures and what needs to be developed for the future? We can drill deviated wells with the large diameters needed to reduce pressure drop. We have cements for temperatures up to about 350C and well designs using casing materials that will withstand the temperature and possible corrosivity of the produced fluids. Casing connections have been an issue in these very hot wells, but advances that include expandable casing connections, advanced thread designs and sealing sections are now available that should solve these problems. Logging tools, instrumentation for measurement while drilling and steering can be heat shielded and run in the cooled wellbore. While zonal isolation using the sliding sleeve devices and packers used in oil and gas is not yet available, setting scab liners using external casing packers (ECPs) with metal to metal seals can allow isolating sections of the well for multizone stimulation. Thermally degradable zonal isolation materials that allow for diversion of fractures both near the wellbore and in the far field can help to create complex fracture networks. While microseismic monitoring, initially developed for the geothermal industry and advanced by the oil and gas industry, is used in geothermal fracture mapping, the temperature range of seismic instruments restricts the potential for deep monitoring. New technology is needed for cementing, logging, directional control, proppants and fracturing fluids and methods to enable multistage fracturing at very high temperatures.

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