Minimization Of Formation Damage, Filter Cake Deposition, & Stuck Pipe Potential In Horizontal Wells Through The Use of Time-Independent Viscoelastic Yield Stress Fluids & Filtrates

Abstract

Abstract Over 60 horizontal wells have been drilled and completed with slotted liners in Prudhoe Bay, Alaska using a low solids or solids-free clarified xanthan/brine drill-in fluid. As previously described the drill-in fluid demonstrates a functional true yield stress (TYS) in the circulating fluid.1 The yield stress is also present in the filtrate, limiting depth of filtrate invasion. The fluid has been further described as being viscoelastic (VE) under static conditions and at the low shear rates exisiting in an expanded plug flow region. This plug flow region is persistent over a wide range of flow rates and is a function of polymer concentration and brine salinity. The exhibits both time-indepent and pseudoplastic properties at higher shear rates (TIP). Collectively the viscoelastic, time-independent pseudoplastic fluid rheology is abbreviated as VETIP.1 Fluid performance has correlated to excellent well productivity, lack of formation damage, minimization of stuck pipe and liners, minimization of filter cake deposition and the lack of mud cake clean-up or removal problems, improved cost-effectiveness, and apparent improvements in present and long term well values. Lack of formation damage, near-zero stuck pipe incidence rates, and minimization of filter cake removal problems are attributed to a functional true yield stress (TYS) in the circulating fluid and filtrate. The yield stress is measurable with oscillatory (Rheometrics), capillary, constant stress, and very low shear rate rotational viscometers. New field and laboratory data correlate well to the yield stress measurements. The yield stress of the filtrate declines with time, thermal degradation, biodegradation, and is quickly broken with hypochlorite breaker, restoring original permeability, without formation damage.