Thermal Property Measurements On Oil Sands

Abstract

Abstract Thermal conductivity and thermal diffusivity properties of oil sand have usually been measured on disturbed core material under ambient laboratory conditions and the measured values are not representative of field conditions at in-situ thermally stimulated production facilities. A transient state thermal test cell for thermal conductivity and thermal diffusivity testing of soil and rock cores has been devised by the authors. The test cell which is specifically designed for thermal property measurements of undisturbed oil sand and shale core samples, has an operational temperature range of 20 °C to 200 °C. Confining pressures up to 10 MPa can be applied to the sample to simulate overburden load and pore fluid pressures up to 10 MPa can be generated within the test cell to ensure fluid saturation of the sample throughout a test. A general description of the test apparatus is given and the thermal conductivity and thermal diffusivity theories and analytical methods used to interpret the test results are outlined. Experimental results for several samples of Athabasca oil sand material are given. Their specific hears are calculated from the results and from the weighted average method and the comparison shows that the test methods and analyses for the thermal conductivity and diffusivity are valid. Results are compared to previously published thermal conductivity measurements on Athabasca oil sands and the importance of the temperature and of the air-water-bitumen saturation is shown. Introduction In-situ thermal methods (such as steam stimulation and in-situ combustion) have been proven to be favorable for the recovery of heavy oil and bitumen from heavy oil and oil sand deposits in Alberta and elsewhere in the world. Many numerical and analytical models for reservoir simulation during heating are available in the petroleum industry. In order that these models can yield meaningful results, correct input parameters that characterize the reservoir are essential. Although the general physical properties of the oil sand deposits are relatively well defined, there appears to be a lack of information on the thermal properties of the materials, particularly at elevated temperature and pressure conditions. With the objective to determine thermal properties of natural oil sand core samples under simulated in-situ conditions, the authors and their coworkers have developed a transient state thermal test cell for the measurement of thermal conductivity and thermal diffusivity on oil sand, shale and limestone cores. Factors Affecting Thermal Properties Table 1 lists all the major factors that affect the three important thermal properties of oil sands, namely thermal conductivity, thermal diffusivity and specific heat. As recognized by many investigators, the material itself (mineral grains, soil structure and density), its degree of saturation and the temperature are significant factors that control the thermal properties of oil sands. There is, however, an uncertainty as to the effects of bitumen and water proportions on the thermal properties of oil sands. Some researchers suggest that there is no significant difference in thermal conductivity whether the non-water phase in the pores is oil or air while others argue that an oil/bitumen parameter should be included for a proper correlation analysis to be made.