Developing new soaking correlation for shale gas wells

Hydraulic fracturing is a well stimulation technique for improved natural gas production from tight gas and shale formations. However, the implementation of the technique brings in new formation damage considerations. During the fracturing treatment, a large volume of water is pumped with proppants into the well. Following the treatment, the well flows back. Only a small fraction of the injected water can be recovered. Over 75% of the injected volume, usually left unrecovered at the start of production that causes permeability damage and productivity impairment. Recently, in some shale formations, some operators have observed improved well performance after an extended shut-in period following initial flow-back of a well that is called the soaking process. This phenomenon is somewhat surprising as shutting in a well after hydraulic fracturing has been traditionally viewed as detrimental to production flow rates (imbibition and water block). This paper will present field cases from different shale formation to investigate the soaking process effect on the well performance. There is still little data in the literature and different behavior for the effect of soaking on gas production from shale formations and the selection of soaking time is still arbitrary. Rate transient analysis (RTA) and decline curve analysis (DCA) were conducted on the production data before and after the soaking process to evaluate the change in the stimulated reservoir area. Finally, a new correlation for the improvement in gas production with the soaking process was proposed. The main conclusion from the long shut-in is an increase in the gas flow rate and reduction in the water rate. Imbibition process during the well shut in spreads of the leaked fluid inside the reservoir far from the fracture interface. Hence, blocking by fracture water around the wellbore reduces and the gas mobility increases. Formation pressure gradient was found to be the more effective parameter on the well performance after soaking, followed by gas specific gravity which is an indication for the thermal maturity for the formation.