Deformation by pore collapse in the Shu'aiba limestone: An experimental study.

摘要

The mechanical properties of the Shu’aiba limestone, the main reservoir in Shaybah field, Saudi Arabia, are investigated in this study. Stresses at failure are measured in the laboratory for cylindrical rock samples taken from the Shu’aiba reservoir. A failure envelope is constructed, from the critical stress states at failure, which shows that this reservoir material is mechanically weak. Experiments are carried out in the conventional uniaxial, triaxial, and hydrostatic compression modes to examine the different failure characteristics of this limestone.; Two main hypotheses concerning the deformation behavior of the Shu’aiba limestone are tested in this study. The first hypothesis deals with failure by a mechanism known as “pore collapse” in which the rock deforms by reduction of pore space. Pore collapse is found to be the dominant mechanism of deformation in this limestone under triaxial and hydrostatic compression loading. The effect of initial porosity on the critical effective pressure at the onset of pore collapse is examined. A linear relationship exists by which the critical effective pressure at the onset of pore collapse can be predicted from initial porosities in the range 20% to 30%.; The second hypothesis states that an increase in temperature should lower the critical effective pressure values that we measure in room temperature experiments for the same material. Conducting experiments at 90°C and 150°C on essentially the same samples used in room temperature experiments shows a considerable drop in critical effective pressures at the onset of pore collapse. Initial porosities are found to be linearly related to the critical effective pressures for the porosity range of 20% to 31%.