Effect of Cyclic and In Situ Heating on the Absolute Permeabilities, Elastic Constants, and Electrical Resistivities of Rocks

Abstract

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Abstract An experimental study was conducted to determine the effects of cyclic and in situ heating on the Young's moduli, bulk moduli, Poisson's ratios, resistivities and Poisson's ratios, resistivities and permeabilities of Berea, Boise, California and Tennessee permeabilities of Berea, Boise, California and Tennessee sandstones. Elastic moduli were calculated by measuring the longitudinal and shear wave transit times of the cores subjected to triaxial pressure. Samples were loaded to 5000 psi overburden pressure at 1000 psi increments, and the pressure at 1000 psi increments, and the confining pressure was kept at 60% of the overburden pressure. Cyclic heating and cooling runs were carried out by placing the cores in steel core holders and heating them at 550 deg. F and 2000 psig pressure in a convection oven. Afterwards, pressure in a convection oven. Afterwards, the cores were placed into the triaxial cell to measure the longitudinal and shear wave transit times. In situ heating experiments were conducted by simultaneously heating the core to 300 deg. F in the triaxial cell and measuring the elastic wave transit times. Permeabilities of dry and saturated cores were measured using the Ruska permeameter. Resistivities were calculated by determining the resistance of the 2% brine saturated sandstones by the aid of a Wheatstone bridge. Longitudinal and shear wave velocities for the sandstones tested decreased as a result of microcracks formed during heating-cooling cycles to 550 F, and in turn, being dependent on the wave velocities, the Young's modulus, bulk moduli, and Poisson's ratios showed significant reductions. In the in situ heating experiments, the decreasing trend of the dynamic elastic constants was less pronounced than that observed in the cyclic heating experiments. Absolute permeabilities of the Berea and Boise sandstones showed progressive increases upon heating to 300 deg. and 500 deg. F, respectively, while the electrical resistivities of all four sandstones exhibited considerable reductions when heated to the same temperatures. Introduction A comprehensive study of a reservoir under thermal treatment warrants a knowledge of the temperature and pressure dependence of the petrophysical properties of the constituent petrophysical properties of the constituent reservoir rocks. In particular, the temperature dependence of the rock elastic moduli plays an important role in the analysis of the thermal stresses induced by the flow of hot fluids in porous rocks. porous rocks.