Effect of Water Salinity on Shale Reservoir Productivity

摘要

It is well known that rocks containing water-reactive clays may swell when contacting with fresh water. In a conventional formation, this swelling may cause wellbore stability problem or damage formation by reducing its permeability. However, the effect of water salinity on shale rocks may be different. This issue is investigated in this paper. Shale rocks were immersed in water of different salinities. Shale rocks used were Mancos, Marcellus, Barnett and Eagle Ford. Different concentrations of NaCl and KC1 salt solutions from 0% to 30% by weight were added in the water. It was observed that Mancos core plugs were crushed into loose grains (fragmented) at low salinity solutions up to 15%. Barnett core plugs showed consecutive cracks along bedding planes at low salinities. Minor cracks were seen on Marcellus, while no visual cracks were found in Eagle Ford core plugs at low salinities. When the shale plugs were saturated with oil, 2% - 15% oil was recovered by water spontaneous imbibition, depending on water salinity and rock mineralogy. Similar observations were made when shale core plugs were applied to an overburden pressure. The results from this paper help us to understand the drive mechanisms in shale oil and shale gas reservoirs. It also stimulates us to explore new ways to improve oil and gas recovery in shale reservoirs.