Soluble-Salt Processes for In-Situ Recovery of Hydrocarbons From Oil Shale

Abstract

This paper describes a class of in-situ shale-oil recovery processes in which permeability and porosity are developed by dissolution of soluble salts. These processes consist of two steps that may be conducted simultaneously or sequentially: leaching of soluble salts and conversion of kerogen. Introduction The presence of large oil-shale deposits in the Green River formation of Colorado, Utah, and Wyoming has been known for more than a century. It also has been long known that the solid organic matter present in these oil shales, known as kerogen, can be decomposed thermally to yield liquid and gaseous fuels. Large amounts of this potential resource can be mined using conventional potential resource can be mined using conventional techniques, and many types of surface retorts have been proposed to recover and collect the thermally generated proposed to recover and collect the thermally generated oil and gas. In-situ retorting of the oil shale also has been considered for many years. Since this oil shale is essentially impermeable to fluids, the major problems associated with in-situ recovery processes are how to apply heat to decompose the kerogen as well as how to collect and recover the fuel products. Many methods, including the use of hydraulic fracturing, mining, and electricity have been proposed to develop permeability and porosity in these oil shales. Once permeability is obtained and maintained, any number of thermal recovery processes can be used to retort the kerogen and recover the resultant shale oil and hydrocarbon gases. The approach presented in this paper for developing permeability and porosity is based on the leaching of permeability and porosity is based on the leaching of water-soluble salts (primarily nahcolite) that have been found to be interspersed in the oil shale in certain sections of the north-central portion of the Piceance Creek Basin, Colo. This paper discusses a field test in which hot water and steam were used to leach the nahcolite and in which steam was used to retort the oil shale to produce shale oil. In-situ combustion and hot-gas pyrolysis methods for converting kerogen to shale oil are suggested as alternatives to pyrolysis with steam and are discussed briefly. pyrolysis with steam and are discussed briefly.A large variety of support work has been necessary to nurture the concept embodied in the soluble-salt processes discussed in this paper from an initial idea through processes discussed in this paper from an initial idea through the development of a recovery process that merited field testing. This paper only touches superficially on the in-depth support work that culminated in the field test and its interpretation, and could hardly do otherwise without becoming too lengthy. Specific areas of support where contributions were pertinent include the following.Identification of the nature and distribution of the soluble salts and of the oil-shale richness.Measurement of the subsurface properties under simulated process conditions.Experimental determination of the kinetics of kerogen decomposition and oil production under simulated process conditions.Solubility measurements under simulated process conditions.Studies on the effect of simulated process environments on the spalling, rubbling, and disaggregating properties of the subsurface oil shale. properties of the subsurface oil shale.Engineering aimed at integrating the individual findings into a technically viable process.Evaluation of the economic potential of process candidates. JPT P. 1078