Comparison of heating methods for in-situ oil shale extraction
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abstract
Oil shales are lamellar, non-porous, impermeable hydrocarbon bearing rocks that contain organic matter called kerogen which, when heated at pyrolysis temperature of approximately 650-700 oF, thermochemically decomposes to liberate hydrocarbons They are at the base of the resource triangle because cutting edge technology and higher fuel prices are required to economically produce them Technologies for oil shale production include surface and m-situ retorting This study focusses on m-situ oil shale production methodologies The process of heating oil shale to the pyrolysis temperature can be achieved by direct or indirect heating Direct heating geometries include the Shell m-situ conversion process (ICP) using downhole electric heaters in vertical holes and the ExxonMobil approach using longitudinal vertical fractures created from horizontal wells and propped with electrically conductive material such as calcined coke Indirect heating approaches propose injection and circulation of steam or a non-condensable gas like CO2 These include the Chevron concept of creating horizontal fractures in vertical wells or the Texas A&M concept using multiple vertical transverse fractures penetrated by horizontal wells The objective of this paper is to compare energy and recovery efficiency of various m-situ retorting technologies using different heating schemes and well configurations as mentioned above Thermophysical parameters like thermal conductivity, specific heat capacity, porosity, permeability needed for the numerical simulation have been obtained by extensive literature survey of various oil shale deposits in Green river formation of USA A sensitivity analysis of direct heating pattern and spacing reproduces previous work Then the validated model is used to evaluate the size and fracture spacing sufficient to heat the oil shale in the direct and indirect heating approaches and to compare pressurized hot fluid circulation to heating elements The use of the same wells for both heating and hydrocarbon production offer an economic edge for indirect heating approaches.
