ABSTRACT
The sub-salt reservoirs are often drilled with OBM, because the WBM’s inherent shortage in rheology and in keeping wellbore stability under HTHP condition. On the other hand, the OBM has a better performance in keeping wellbore stability under high temperature. The creeping of salt under WBM has been investigated in variety of studies (Fabre 2006). Some scholars have proposed several different equations for expressing the relationship between stress creeping rate and temperature (Homand 2006). In studies concerned with the micro mechanics of salt creeping, Fredrich (2007) employed statistics analysis on experimental data obtained from the salt rock experiments of Gulf of Mexico. Fuenkajorn (2010) analyzed the changes of Young’s modules, and Poison’s ratio on salt rock under repeated load and unload procedures. Popp (2000) investigated the changes of rock’s permeability and acoustic logging data under different stress load. In the studies concerned with the interaction between salt and drilling mud, Chen, X. analyzed the salt dissolving under WBM (Chen et al. 2011). De Meer, S. & C.J. Spiers studied the creeping rate of salt formation under WBM (De et al. 1999). G & Baoping proposed a theoretical model incorporated the couple effects of thermal conduction and fluid infiltration on salt formation (Bao et al. 2008). To sum the above studies up, the previous studies have concluded that when the stress loading increases, the pre-existed internal micro cracks will expend (Chan et al. 2001). And because of this change, the permeability of the rock
microscope scanning, we can visualize the micro scale structure of the rock. As the picture shows Figure 1, there are a lot of micro cracks existed in the salt rock. From this sample, we can see a complex net work of salt and plaster. From Figure 1b we can see the feature of salt and plaster in the salt rock in micro scale respectively.
