| Description |
Oil shales are a complex sedimentary aggregation of organic and inorganic materials; the organic materials are referred to as kerogen. The kerogen, a petroleum predecessor, can be decomposed into liquid hydrocarbons, gases, and residual solids (coke) through the process of pyrolysis, in which extremely high temperatures are applied to the shale in situ and without oxygen. The resultant liquid and gaseous products are moved from the pyrolyzed reservoir to one or more wellbores due to imbalances in pressure or similar mechanisms (drive mechanisms). In oil shale, expansion drive could result from generation of oil and gas; compaction drive could result from pore creation and the concurrent reduction of material integrity. The problem is that the process of pyrolysis and extraction can weaken the underground shale, potentially causing subsidence/heave, which is a reduction/increase in surface elevation due to a compaction/thermal expansion of a formation at depth. This research describes an experimental program that was developed to demonstrate how the mechanical and transport properties of representative oil shales from the Green River Formation evolved up to, through and after in situ pyrolysis. A primary goal of this experimental campaign is to provide information related to mechanical properties of oil shale as a function of the grade, temperatures and the in-situ stress conditions. The program also sought to advance the understanding of drive mechanisms (compaction and expansion), subsidence/heave, and transport/storage (permeability/porosity) prior to and after pyrolysis. iv This work focuses on evaluating the impact of temperature, confining pressure (in-situ stress magnitude), and grade of the oil shale. The laboratory analyses provide values for Young's modulus, Poisson's ratio, and strength. Numerical simulations and multi-variable regression similarly duplicate and predict these parameters for interpolation and prediction of properties at conditions not considered in the laboratory testing. Comparisons with experimental data are provided and evaluated. A key aspect of the effort is to provide engineering information that could be used for future predictions of efficiency of different in situ extraction methods. The information acquired was consolidated using multivariate analyses. This gave an interpolative technique for prediction of the effects of varying grade, confining pressure, and temperature. |
