Experimental Study of Wettability Alteration in Unconventional Reservoirs to Enhance Clean-Up after Hydraulic Fracturing
Muhammad Harith Azahari and Shamsul Azhar Mohd - 2014
Australian School of Petroleum
University of Adelaide
Low permeability that is characteristic in unconventional reservoirs causes the ultimate recovery of the reservoirs to be very low. Therefore in order to produce gas at an economic rate from the unconventional reservoirs, hydraulic fracturing must be applied. The water based fracturing fluid injected during hydraulic fracturing causes water blocking. The water invades into the formation and is strongly held in place by high capillary pressure. The water invades into the formation and is strongly held in place by high capillary pressure. Theoretically, this water blockage can be solved by lowering the capillary pressure to a lower value. There are some parameters that contribute to the capillary pressure such as interfacial tension, contact angle and effective pore radius. From the literature that had been studied, two surfactants which are ALFOTERRA 123-4S and NOVEL TDA-12 Ethoxylate plays a major role in changing the contact angle of the water-gas system.
In this experimental study, the main focus is to reduce the capillary pressure by changing the contact angle of a water-gas system on core samples. Experiments were performed on few cores of the tight gas sand and shale reservoirs to study the effect of temperature, distilled water and salinity on the contact angle of the cores. The experiments were conducted by using Optical Contact Angle measuring instrument OCA 15EC, a video-based technology. This experiment involves analysing the contact angle made by a drop of water dispensed on the surface of core samples. The moving water drop will be recorded in both the video and image format, and the contact angle of the stabilised water drop of water will be measured using SCA software.
The first experiment of the contact angle test shows that an increase in temperature will decrease the contact angle of the water drop. The results show that the contact angle of the cores is reduced in the range of 3.5° to 8.95°. The second experiment with the distilled water shows that the contact angle had an increment in the range of 8° to 25°. Lastly, the effect of salinity shows a significant increase in contact angle as the salinity of the fluid increases. The same trend can be observed from the result of the experiments conducted on the shale core samples. The result of this study can aid in the understanding of the contact angle based on the effect of three parameters tested on the cores.
The experiments done throughout this study is considered as the base case study which would be useful to give an insight for further analysis in the future regarding unconventional reservoirs.