Comparison of Heating Methods for In-Situ Oil Shale Extraction

摘要

Oil shales are lamellar, non-porous, impermeable hydrocarbon bearing rocks thatcontain organic matter called kerogen which, when heated at pyrolysis temperature ofapproximately 600-800 ?, thermo-chemically decomposes to liberate hydrocarbons.They are at the base of the resource triangle because cutting edge technology and higherfuel prices are required to economically produce them.Technologies for oil shale production include surface and in-situ retorting. Thisstudy focuses on in-situ oil shale production methodologies. The process of heating oilshale to the pyrolysis temperature can be achieved by direct or indirect heating. Directheating geometries include the Shell in-situ conversion process (ICP) using down holeelectric heaters in vertical holes and the ExxonMobil Electrofrac (EF) approach usinglongitudinal vertical fractures created from horizontal wells and propped withelectrically conductive material such as calcined coke. Indirect heating approachespropose injection and circulation of steam or a non-condensable gas like CO_(2). Theseinclude the Chevron CRUSH concept of creating horizontal fractures from vertical wellsor the Texas A&M University (TAMU) concept using multiple vertical transversefractures penetrated by horizontal wells (MTFH).The objective of this study is to compare energy efficiency of various in-situretorting technologies for different heating schemes and well configurations using thecommercial adaptive-implicit thermal simulator, STARS of Computer Modelling GroupLtd. (CMG). STARS is a three phase multi-component thermal simulator and is based onvapor-liquid distribution ratio of a component, K values to perform phase equilibrium calculation instead of using the Equation of state (EOS). Shell has applied CMG ?STARS to model its in-situ upgrading project, but is yet to publish details on the input parameters used for modeling. As such, the various thermo-physical parameters like thermal conductivity, specific heat capacity, porosity, permeability needed for the numerical simulation are obtained by extensive literature survey of various oil shale deposits in Green river formation of USA.Using CMG ?STARS, we have built and validated simulation model to replicate Shell?s in-situ Conversion Process (ICP) in the Mahogany Demonstration Project South (MDPS). 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 other direct and indirect heating approaches and to compare pressurized hot fluid circulation to heating elements on terms of hydrocarbon production and energy efficiency while keeping all the model inputs similar for each method. This research also enables oil shale well design recommendations for direct and indirect heating methodologies considering the depth of the reservoir and, for indirect heating, the pressure and temperature for the circulation fluid.