Development of Unique, Non-Damaging, Non-Crosslinked Solids Cleanout Fluid System with Enhanced Solids Suspension Capacity

Abstract

Traditional, natural polymer-based fluid systems, used for wellbore cleanout applications have several characteristic limitations related to temperature degradation, solids transport capacity, energized applications foam stability and are always a source or risk if circulation is interrupted, due to lack of static suspension capability. The objective was to create a synthetic polymer-based fluid system which has enhanced properties when compared to the natural polymer based linear gels traditionally employed in wellbore cleaning.

The characteristics of the novel fluid system were investigated through a series of experiments including rheology and suspension testing vs. polymer concentration and with various types, sizes and grades of proppant in both foamed and non-foamed conditions. Fluid performance was subsequently validated via multiple field trials at depths from 800m to 3,000m.

The unique system has significantly enhanced suspension and carrying capacity resulting in reduced cleanup times, material consumption and cost. The new system mitigates any requirement for "viscosified pill" sweeps. The system can be energized and when doing so creates foams which are stable at surface and at BHT (bottom hole temperature). The energized systems remain stable even when created with a very low foam quality and have inherent friction reduction properties. The ECD (equivalent circulation density) across potential loss zones can be readily controlled by adjusting the foam quality and thereby preventing any potential formation damage associated with fluid lost to formation. Furthermore, the fluid is non-crosslinked and non-damaging. The polymer utilized in this novel system is a fast-hydrating polymer which can be mixed "on the fly" or batch mixed. All the above translate to increased wellbore cleaning efficiency.

This unique and innovative non-crosslinked low viscosity system is characterized by its ability to suspend solids even under static conditions at raised temperatures. Typical cleanout linear gels require a minimum rate be maintained to prevent solids fallback and have limited carrying capacity. This novel system greatly reduces such rate and has a greatly increased solids carrying capacity.