A review of crosslinked fracturing fluids prepared with produced water

The rapidly increasing implementations of oilfield technologies such as horizontal wells and multistage hydraulic fracturing,particularly in unconventional formations,have expanded the need for fresh water in many oilfield locations.In the meantime,it is costly for services companies and operators to properly dispose large volumes of produced water,generated annually at about 21 billion barrels in the United States alone.The high operating costs in obtaining fresh water and dealing with produced water have motivated scientists and engineers,especially in recent years,to use produced water in place of fresh water to formulate well treatment fluids.The objective of this brief review is to provide a summary of the up-to-date technologies of reusing oilfield produced water in preparations of a series of crosslinked fluids implemented mainly in hydraulic fracturing operations.The crosslinked fluids formulated with produced water include borate-and metalcrosslinked guar and derivatized guar fluids,as well as other types of crosslinked fluid systems such as crosslinked synthetic polymer fluids and crosslinked derivatized cellulose fluids.The boratecrosslinked guar fluids have been successfully formulated with produced water and used in oilfield operations with bottomhole temperatures up to about 250
F.The produced water sources involved showed total dissolved solids(TDS)up to about 115,000 mg/L and hardness up to about 11,000 mg/L.The metal-crosslinked guar fluids prepared with produced water were successfully used in wells at bottomhole temperatures up to about 250
F,with produced water TDS up to about 300,000 mg/L and hardness up to about 44,000 mg/L.The Zr-crosslinked carboxymethyl hydroxypropyl guar(CMHPG)fluids have been successfully made with produced water and implemented in operations with bottomhole temperatures at about 250t
F,with produced water TDS up to about 280,000 mg/L and hardness up to about 91,000 mg/L.In most of the cases investigated,the produced water involved was either untreated,or the treatments were minimum such as simple filtration without significantly changing the concentrations of monovalent and divalent ions in the water.Due to the compositional similarity(high salinity and hardness)between produced water and seawater,crosslinked fluids formulated with seawater for offshore and onshore jobs were also included.The crosslinked guar and derivatized guar fluids have been successfully formulated with seawater for operations at bottomhole temperatures up to about 300
F.Operating costs have been significantly reduced when produced water or seawater is used to formulate fracturing fluids in place of fresh water.With various challenges and limitations still existing,the paper emphasizes the needs for new developments and further expansion of produced water reuse in oilfield operations.

Enhanced gelled hydrocarbon well treatment fluids

Compared with water-based well treatment fluid systems,hydrocarbon-based fluids possess advantages such as better fluid compatibility and lower formation damage,especially in water-sensitive formations.Hydrocarbonbased fluids are therefore often used in oilfield operations including hydraulic fracturing,sand control,and coiled tubing cleanout.The metal-crosslinked,phosphate ester-based gelled hydrocarbon(or gelled oil)fluids have been the preferred choice among hydrocarbon-based fluids since they are cost effective,robust at elevated temperatures,and operationally simple as only a couple of fluid additives are involved.Functioning as the gelling agent in gelled oil fluids,phosphate ester could cause fouling in refinery equipment.It is therefore desirable to lower the dosage of the phosphate ester-based gelling agent as much as possible,but without adversely affecting the fluid performance.A number of materials have been identified that could enhance the gelled oil viscosity and stability,which in turn translates into the reduction of the phosphate ester needed in the gelled oil.Among these enhancing materials,a type of aluminum pillared montmorillonite clay(the additive)was found to enhance the gelled oil viscosity to the largest extent.In laboratory tests,30 ppt(30 pounds per thousand gallons)of the additive increased the gelled oil viscosity by 84%(±5%)at 250°F when compared with the baseline gelled oil without the additive.With the additive dosage at 30 ppt,the amount of the phosphate ester in the gelled oil could be reduced by 25%without decreasing the fluid viscosity.The additive was successfully applied to the crude oil-based gelled fluid,resulting in multiple times of viscosity increase in the study.In addition to the gelled oil viscosity enhancement,the additive also increased the regained permeability in the coreflow tests to near 3 times.