Experimental study of the swelling properties of unconventional shale oil and the effects of invasion on compressive strength

In the industry as a whole, we are still at the beginning of the learning curve for shale oil drilling operations; however, many shale-oil wells have been drilled in recent years. Drilling through shale-oil formations is very problematic and imposes significant costs to the operators owing to wellbore-stability problems. These problems include, but are not limited to, tight holes, stuck pipe, fishing, sidetracking, and well abandonment. To more efficiently and effectively drill through these formations, we should better understand their properties. Few experiments have been performed on shale-oil samples to better understand their properties. Most experiments conducted thus far were performed on common shale core samples, which are significantly different from shale oil samples. In this study, we first determined the mineralogy of shale-oil core samples from the Eagle Ford field and then investigated the swelling properties and Cation Exchange Capacity (CEC) of the core samples in the laboratory. Experiments have been conducted with the samples partially submerged in distilled water and potassium-chloride (KCl) brine. Several experiments have been performed using strain gages to measure lateral, axial, and diagonal swelling in both submerged and non-submerged areas. The results demonstrate that the swelling properties and CEC of the shale oil core samples are different from the common shale core samples. This study proposes the quantification of the shale/fluid properties, the interaction, and the effects of different fluids on rock properties in unconventional reservoirs. This paper presents and documents the differences in the swelling properties between conventional and unconventional shale. The results of the study will help us to more precisely understand unconventional shale oil rock properties and can be used to design a more effective drilling fluid for field applications, as well as more accurately predict the mechanisms of formation failure.