The Impact of Salinity on Water Dynamics, Hydrocarbon Recovery and Formation Softening in Shale: Experimental study

摘要

The low reocvery of Slick water used in hydraulic fracturing treatments and the better performance observed for low salinity floods reveal the impact of water dynamics on well and reservoir performance. The focus of this study has been to develop and implement an experimental workflow to investigate the impact of water salinity on wettability, hydrocarbon recovery and formation softening in shale rock samples varying in mineralogy. We are trying to provide a better understanding of the mechanisms of water dynamics and entrapement along with the driving forces associated with these mechanisms. Samples from Woodford and Caney outcrops in the Unites States of America were obtained. The mineralogy of the cores was measured using the FTIR technique. While the Woodford samples turned out to be Dolomite rich, the Caney samples were Quartz and clay rich. Spontaneous imbibition and contact angle measurements were conducted for these samples using slickwater with an added KCl weight percentage of 0, 5 and 10. Both the rock-water-gas and the rock-water-oil systems were examined. The formation softening was quantified by recording the rock mechanical parameters before and after the imbibition and soaking tests. The results were analyzed in terms of the capillary suction characteristics for each formation. According to the experimental results, a positive correlation was observed between water salinity and imbibition in Caney formation. However, the opposite was observed for Woodford samples. The formation mineralogy was identified to be the major factor in this reversal of wettability. Similar trends were observed for the recovery of both oil and gas where the low salinity imbibition yielded a higher recovery factor for the Caney formation samples and a lower recovery factor for Woodford. In addition, tangible increase in the compressive strength of Caney formation was reported with the increase in KCl concentration. However, a non-monotonic trend was observed for Woodford samples. This study provides insights into the water dynamics in ultra-low permeability reservoirs. The formation mineralogy is a key factor for properly describing the water dynamics whether in fracturing treatments or in low salinity flooding projects. Low salinity flooding does not always imply better hydrocarbon recovery, based on what we observed in Woodford samples.