ABSTRACT

Petroleum reservoir rocks that are buried at depths are subjected to internal stresses exerted by fluids (e.g., gas, oil, and water) that are present in the pore spaces and the external stresses which are in part exerted by the overlying rocks.1 However, petroleum reservoirs are dynamic systems that are constantly changing as fluids are depleted from the pore spaces as part of production. This depletion causes the change in the internal stress, thus resulting in the rock to be subjected to a different resultant stress.1 Similarly, during water flooding or gas injection, the equilibrium rock stresses can also be altered in a dynamic manner. Injection of external fluids results in an increase in pore pressure and a decrease in net effective stress. The knowledge of changes of net effective stress is an important element of reservoir management because the alteration of the net effective stress during production can have significant impact especially on stress-sensitive reservoirs. Predicting the mechanical behavior of reservoir rocks is essential for well completion and stimulation programs.2 Additionally, reservoir compaction, which may lead to surface subsidence, is a critical factor with respect to design of the casing platforms and to the overall performance.3 These types of rock characteristics are normally evaluated by measuring various mechanical properties of reservoir rocks. Tiab and Donaldson2 have covered this topic in extensive detail.