Investigation of effects of temperature and swelling on wellbore stability in unconventional reservoirs

The industry is 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 may 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 un-derstand their properties. Few experiments have been performed on shale-oil samples to better under-stand their properties. Most experiments conducted thus far were performed on com-mon 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 Capaci-ty (CEC) of the core samples in the laboratory. Experiments have been conducted with the samples partially submerged in distilled water, potassium-chloride (KCl) brine and Oil-Based Mud (OBM). Several experiments have been performed using strain gages to measure lateral, axial, and diagonal swelling in both submerged and non-submerged areas. To simulate actual well conditions a High Pressure, High Temperature (HPHT) core holder was used to apply different axial and radial confining stresses, equivalent formation pore pressure, and drilling fluid wellbore pressure. The experiments were conducted under elevated temperatures to better mimic real drilling operations. Satu-rated shale oil core samples from the Eagle Ford field were tested under various tem-peratures including reservoir temperature. I also performed Unconfined Compressive Strength (UCS) tests were performed to investigate the effect of temperature on the compressive strength of the core samples. The experimental setup was modified to ac-commodate five Linearly Variable Displacement Transducers (LVDTs) to measure Young’s Modulus (E) and Poisson’s ratio (ν). Various experiments were run to quanti-fy the effect of temperature on the rock compressive strength, E, and ν. Experiments have shown a distinct change in the mechanical properties of the rock.