*4.1.2 Oil-based fracturing fluid*

Oil-based fracturing fluids are used mostly where a formation is water-sensitive perhaps due to the presence of large quantities of expandable clay minerals. Oilbased fracturing fluids have been found to better preserve fracture conductivity [54, 55] as well as provide better performance in terms of proppant transport due to the generally higher viscosity and lower specific gravity. In their work on wells located in Bakhilov and North Khokhryakov fields in Western Siberia, Russian Federation, Cikes et al. [54] studied the responses from wells after treatment with oil-based fracturing fluids in a depleted oil reservoir. These wells were initially fractured with water-based fracturing fluids but the treatment failed and did not yield

### *Review of Geochemical and Geo-Mechanical Impact of Clay-Fluid Interactions Relevant… DOI: http://dx.doi.org/10.5772/intechopen.98881*

significant improvements in the productivity especially for the long term. Following fracturing with oil-based fracturing fluids, over ten-fold production improvement was witnessed relative to pre-fracturing productivity.

Another advantage of oil-based fracturing fluids as noted by Hlidek et al. [56] is that they are easier to clean-up and can be re-used. Hlidek et al. [56] compared the cost of using water-based fracturing fluids to oil-based fracturing fluids in the Montney (Canada) unconventional gas development. Based on their comprehensive analysis, they concluded that the cost of using oil-based fluids was lower in the long term since all the load oil could be recovered within 4 to 8 weeks and could be reused in fracturing. The main disadvantage of oil based fracturing fluids however, is environmental damage when not properly disposed of.

To enhance the efficiency and recovery of oil-based fracturing fluids, CO2 has been employed in energising these fluids. Energising oil-based fluids significantly reduces the amount of fluid required to fracture a specific formation as well as aids in fluid recovery following the fracturing process [57, 58]. Vezza et al. [58] studied the impact of energised oil-based fracturing fluid in Morrow Formation in Southern Oklahoma where they used gelled diesel/CO2 as fracturing fluid. Their results indicated an overall increase in production rate and predicted long-term stability of the wells. Gupta et al. [57] also reported improvements in well productivity and stability after using energised gelled hydrocarbons in fracturing treatments. In their study, they compared the use of conventional gelled fluids to CO2 energised gelled fluids in formations in Canada. Their conclusions were that: The use of energised gelled hydrocarbon fracturing fluids led to improved production relative to conventional gelled hydrocarbon fluids.
