Is water saturation a fracability indicator for organic‐rich, yet low‐clay content, tight carbonate source rock reservoirs?

Abstract

AbstractHydraulically fracturing long horizontal wells is the key technology for economically producing hydrocarbon from unconventional reservoirs. A reservoir's fracability (the ease by which it can be hydraulically fractured) has often been used as an important parameter for identifying the sweet spots for production. Several fracability indicators, based on different types of rock properties, including mechanical, geochemical, and mineralogical properties, have been developed and used in industry. This study, based on observations from a source rock reservoir, proposes the use of reservoir water saturation as a new fracability indicator for organic‐rich tight carbonate source rocks that are not clay rich. The results from a machine learning model trained with the observations clearly show the strong and positive correlation between the linear flow parameter (that is obtained based on the newly proposed equivalent‐state approximation and characterizes the effectiveness of hydraulic fracturing) and the water saturation for oil wells, but not for gas wells. While further investigation is needed, the results may be due to the dual wettability of the carbonate source rock. Since minerals are more water‐wet than the organic matter, reservoir water tends to occupy pore spaces in the mineral matrix. Thus, water saturation reflects the relative portion of mineral matrix pore spaces. Given that the low‐clay content mineral matrix contains all the brittle components, the pore‐space development in the mineral matrix may have important implications for the fracability in the hydraulic fracturing process.