Abstract
In this work, we first studied the thermal damage to typical rocks, assuming that the strength of thermally damaged rock microelements obeys a Weibull distribution and considering the influence of temperature on rock mechanical parameters; under the condition that microelement failure conforms to the Drucker–Prager criterion, the statistical thermal damage constitutive model of rocks after high-temperature exposure was established. On this basis, conventional triaxial compression tests were carried out on oil shale specimens heated to different temperatures, and according to the results of these tests, the relationship between the temperature and parameters in the statistical thermal damage constitutive model was determined, and the thermal damage constitutive model for oil shale was established. The results show that the thermal damage in oil shale increases with the increase of temperature; the damage variable is largest at 700°C, reaching 0.636; from room temperature to 700°C, the elastic modulus and Poisson’s ratio decrease by 62.66% and 64.57%, respectively; the theoretical stress-strain curve obtained from the model is in good agreement with the measured curves; the maximum difference between the two curves before peak strength is only 5 × 10−4; the model accurately reflects the deformation characteristics of oil shale at high temperature. The research results are of practical significance to the undergroundin situthermal processing of oil shale.
Highlights
Oil shale resources are abundant and, when converted into shale oil, will amount to more than 400 billion tons, which is approximately three times the proven recoverable reserve of natural crude oil
We first studied the thermal damage to typical rocks, assuming that the strength of thermally damaged rock microelements obeys a Weibull distribution and considering the influence of temperature on rock mechanical parameters; under the condition that microelement failure conforms to the Drucker–Prager criterion, the statistical thermal damage constitutive model of rocks after high-temperature exposure was established
There are more than ten in situ thermal processing techniques, the core of which relies on heating of the underground oil shale reservoir to produce oil and gas by pyrolysis of kerogen in oil shale and recovering oil and gas to the surface [5, 6]
Summary
Oil shale resources are abundant and, when converted into shale oil, will amount to more than 400 billion tons, which is approximately three times the proven recoverable reserve of natural crude oil. To use the oil shale resources, many methods of exploitation of oil shale have been developed, which can be roughly divided into two categories: surface retorting and in situ thermal processing. It is important to study the thermal damage to oil shale and establish an appropriate constitutive model thereof [7,8,9]. Based on the concept of rock yield, the model parameters were determined by the extremum method On this basis, according to the results of conventional triaxial compression tests of oil shale specimens after heating to different temperatures, the relationship between temperature T and parameters in the statistical thermal damage constitutive model of oil shale after high-temperature exposure was determined by means of a mathematical fitting method, and the thermal damage constitutive model of oil shale was established. On this basis, according to the results of conventional triaxial compression tests of oil shale specimens after heating to different temperatures, the relationship between temperature T and parameters in the statistical thermal damage constitutive model of oil shale after high-temperature exposure was determined by means of a mathematical fitting method, and the thermal damage constitutive model of oil shale was established. e correctness of the model was verified by comparing the theoretical stress-strain curve calculated from the model to the actual curve measured by conventional triaxial tests
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