Thermophysical Properties Of Devonian Shales

Abstract

Abstract A detailed study of the thermophysical properties of Devonian shales from the central and eastern United States has been carried out. The properties encompass a wide spectrum of material properties such as thermal conductivity, thermal diffusivity, specific heat, dielectric constant and sonic velocities. The importance of such measurements in on-field applications in oil shale technology is highlighted. Comparison of the trends in the various properties observed for Devonian shales as a function of temperature with data obtained previously for Green River oil shales is presented. previously for Green River oil shales is presented. Similarities and differences in the thermophysical behavior of the two types of shales are discussed. Introduction Gas-bearing oil shales of Devonian age occur extensively in the central and eastern United States. These shale deposits represent an important potential source of natural gas. Estimates of oil and gas potential of Devonian shales are somewhat variable potential of Devonian shales are somewhat variable although they are in the neighborhood of several hundred trillion cubic feet of gas. Thermophysical characterization of Devonian shales is relevant to the development and optimization of methods that are currently envisaged for the recovery of natural gas from these deposits. Most of these methods rely on the application of heat to pyrolyze the organic constituents of the shale. An understanding of the effect of temperature on the properties of these shales is thus crucial for efficient process design. The term "thermophysical" is used in the present context to represent those parameters which are directly or indirectly related to parameters which are directly or indirectly related to the transport, absorption or release of heat. Properties such as thermal conductivity, thermal diffusivity Properties such as thermal conductivity, thermal diffusivity and specific heat fall naturally into this definitive classification scheme. For materials like oil shales which are thermally active, i.e., those which undergo thermal decomposition or phase transformation, it is also useful to characterize their thermal behavior by techniques such as Differential Scanning Calorimetry (DSC). Electrical and mechanical properties have customarily become an integral part of thermophysical characterization in view of their extreme sensitivity to changes taking place in the material on application of heat. The present article focuses on the above aspects of the thermophysical behavior of Devonian shales. A wide spectrum of measurement parameters has been employed to yield a self-consistent picture on the overall thermophysical behavior of these oil shales. The properties that were measured, the techniques employed and the relevance of these experimental results in some typical on-field applications are listed in Table 1. The work reported in this paper represents the first instance of a complete thermophysical characterization of Devonian shales. In previous papers from this laboratory, the electrical, thermal and mechanical behavior of Green River oil shales was reported. In this article, comparisons of the various aspects in the thermophysical behavior of those shales with the corresponding trends for Devonian shales will be highlighted. EXPERIMENTAL a) Samples: Measurements were performed on cored oil shale samples of appropriate dimensions that were drilled from crack-free massive blocks. Michigan shales were obtained from wells drilled in Sanilac County with core depths ranging between 1303 - 1306 ft. Kentucky oil shale samples were obtained from the Sweetland Creek member (core depth: 2016–2040 ft, average thickness 24 ft) of the New Albany deposits. The Green River oil shale samples were selected from cores drilled in the Anvil Points and Logan Wash deposits. The coring direction was nominally perpendicular to the stratigraphic planes of the shale. perpendicular to the stratigraphic planes of the shale. Oil yields of the various shale samples were obtained from pulsed NMR assay. All samples were carefully dried in pulsed NMR assay. All samples were carefully dried in vacuum at room temperature prior to measurement. Repeatability of the experimental results and any possible variations arising from compositional possible variations arising from compositional inhomogeneity of the shale, were systematically checked by duplicate runs on samples cored at approximately 19 mm intervals from the blocks (vide infra). b) Techniques: An outline of the various techniques employed for the thermophysical characterization (cf Table 1) is given below. Details of the measurement systems, calibration etc. are reported elsewhere.