Surfactant system for water-based well fluids

Water-based fluids are used at different steps of well construction, i.e. drilling, completion or hydraulic fracturing, generally due to strong local environmental concerns. A prominent area of research is damage caused by water soluble polymer and/or brine filtrate invasion into the producing formation. It is common knowledge within the petroleum industry that, in conditions called overbalanced when the pressure of the fluid is maintained above the formation pressure, filtrate invasion into the pore spaces of a reservoir is continuous as long as the fluid and wellbore are in contact. It is also commonly known that depending on their chemistry and molecular weight, some polymers tend to adsorb or to be retained, and sometimes plug, the water-wet linings of reservoir pores. Once this occurs, flow paths are restricted and formation permeability is impaired. Despite the careful selection of less damaging polymeric viscosifiers and fluid loss agents, reduced mobility of production fluids remains a problem. Depending on the compatibility of the aqueous filtrate with the reservoir fluids specially viscous heavy oils, strong water-in-oil emulsions may be formed and also plug reservoir pores.A surfactant molecule engineered to pass through a drill-in fluid filter cake along with the other filtrate components was selected to maximize wellbore productivity. Functionally, this chemistry (1) prevents the irreversible adsorption of the fluid polymers on the in situ surface areas of the reservoir, (2) reduces the water saturation level of the formation rock to increase flow area, (3) promotes compatibility between the brine filtrate with formation crude, and (4) reduces the adhesion properties between filter cake particles to enhance the ease of wellbore clean up during displacement and natural cake “lift-off” during the onset of production.