Thermal stress of carbonate rocks: An experimental approach

Abstract

The most commonly used methods of describing fluid flow in oil reservoirs use constant rock properties. However, these methods are not applicable to reservoirs that undergo changes in the rock properties due to variation in pore pressure. A common characteristic of fractured reservoirs is sensitivity of permeability and porosity to effective stress. The in-situ stress, in itself, can be of mechanical or thermal origin. The thermal stress can be significant in thermal enhanced oil recovery schemes, injection of cold fluid in hot formation during water flooding or wastewater disposal, or during hydraulic fracturing.

An extensive literature review reveals that the research in this area has focused only on thermal recovery of heavy oil. Little has been done to investigate the onset and propagation of fractures under thermal stress or even mechanical stress. Consequently, this paper is devoted to investigate fracture development and propagation in carbonate formation under thermal and mechanical stress. A series of experiments were ingeniously designed to study the effect of thermal stress on fractured carbonate formation. Laboratory experiments were conducted to determine stress-strain relationship and their time dependence, fracturing and propagation of fractures. A computer image analyzer was used to observe the fracture/fissures distribution for various cases of thermal stress on carbonate rocks. The role of thermal and mechanical stress in determining orientation and propagation of fractures was also studied.