Experimental study of mechanisms of improving oil recovery in Shale
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ABSTRACT Extensive laboratory work was done to investigate some of the important mechanisms of improving oil recovery in Shale formations. The objective of this research is to determine the most effective water solution, for a particular Shale formation, that will promote the displacement of oil, by inducing swelling and minor water fractures in the Shale formation, and thus creating open channels. These fractured channels will provide links to natural fractures existing in the Shale and hence permit the flow of oil and gas from the Shale to the production well. Using spontaneous and forced displacements, distilled water, brines and hydrochloric acid solutions with different water concentrations were examined. Soltrol-130 oil was used in place of the formation fluid. Experiments directed towards this goal involved two exclusive processes. First was altering the solution salinity, and the next was altering the solution acidity, of a water displacing fluid. Subsequent to these steps, was to spontaneously displace the oil in the Shale cores by these water solutions of varying salinities or acidities. The Shale cores used in this experiment have ultra-low porosity and permeability and were gotten from Mancos, Eagle-Ford, Marcellus and Barnett formations. There were eight key observations noted from this experimental study: (1) Cores at low salt concentrations (0-10% wt of NaCl and KCl) induced more cracks and fractures, that resulted in whole core damage, in comparison to cores immersed with higher salt concentration. (2) At the same low concentration percentage NaCl solution would permit more factures than a KCl solution. (3) At 30% NaCl Concentration, the cores were difficult to fracture using only water and spontaneous displacement. (4) The highest oil recovery factor is from the lowest solution salt content which resulted from clay swelling. (5) The oil flow path along the cores could be seen after saturation with Soltrol-130 oil. (6) The effect and extent of water fracturing on Shale depends on the presence of natural factures, type and amount of clay composition in the Shale (7) Addition of HCl increases the creation of fractures. (8) The oil recovered much easily and faster in the cores with much cracks and fractures compared with the cores with less fractures and cracks. Hence for a given formation the optimal brine solution concentration and HCl solution concentration could be determined for the most effective water to oil displacement process.