It is known from industrial experience that the majority of the hydraulic fracturing treatment water used to stimulate gas production in shale reservoirs is lost to the shale and does not return to the surface. Water imbibition in low permeability reservoirs usually results in reduced reservoir gas production, however, shale gas production has been demonstrated to be positively correlated with the amount of water imbibed by the shale. It is predicted that the different surfactants in the hydraulic fracturing fluid dictate the water/shale interaction and by extension, the reservoir productivity, although the detailed adsorption behavior in these complex fluids is poorly understood. Here we use contact angle & surface tension measurements to study the change in wettability of Marcellus shale due to interaction with commonly used surfactants in hydraulic fracturing completion fluids. Cationic octadecyl trimethyl ammonium chloride (OTAC) and anaionic ammonium Dodecyl Sulfate (ADS) were selected for this study due to their regular use in hydraulic fracturing fluids and also due to their well reported mixing behavior. The individual as well as mixed surfactant adsorption behavior were studied by varying the total surfactant concentration, mixing ratio, solution pH and salinity. Results indicate that the OTAC/ADS surfactant mixture alters the Marcellus shale wettability to a greater degree than either of the individual surfactants at equivalent concentrations. This is due to the mixed surfactant synergism and non-uniform charge distribution on the shale surface. By varying the total mixed surfactant concentration across the mixed critical micelle concentration we can tune the shale surface wettability based on different surfactant adsorption mechanisms.

Effect of surfactant adsorption on shale wettability

251st National Meeting (2016)

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