Lost circulation is one of the main causes of nonproductive time during drilling and impacts the success of cementing operations. Losses into the reservoir not only impact drilling, they potentially impact the reservoir, due to influx of quantities of drilling fluids that are potentially damaging, or will influence the production rate. Existing solutions are based mainly on particulates, which often are added to drilling fluids to plug fractures or to build up filtercake to cure fluid losses. When particulates are applied for curing losses in reservoir sections, it is desirable that the plugging materials maintain stability for sufficient time to allow well completion but eventually self-degrade to leave undamaged formation for future hydrocarbon production. The main challenges are the design of the lost-circulation material to cure losses into fractures of various widths and to provide plug stability and cleanup within a desired time frame over a broad bottomhole temperature range.Fibers have shown good fracture-plugging behavior. Parameters affecting fiber performance include, but are not limited to, fluid viscosity, fiber concentration, fiber geometry, flow rate, effect of the wall, and fracture width. To effectively apply fibers as lost-circulation applications, a novel, fiber-laden fluid was designed for easy preparation on surface, allowing compatibility with bottomhole assemblies (BHAs). The decrease in velocity inside the fracture enables fibers to bridge and then plug the fracture, thus regaining circulation. The fibers are specially designed to degrade in an adjustable time frame sufficient to ensure plug stability until the well is completed. With time, the plug undergoes further degradation, leading to nondamaged formation for production.This novel degradable solution has been successfully proven during field trials in various drilling scenarios ranging from severe to total losses with effective and efficient loss mitigation, without issues on placement through BHA and bit nozzles, and mitigating further reservoir damage.

Oilfield produced water usually comprises both the formation water and injected fluids from prior treatments. Produced water may be environmentally hazardous and usually contains bacteria, hydrocarbons, and high levels of dissolved salts. As such, the proper disposal of produced water is often expensive. Meanwhile, fresh water used to formulate oilfield treatment fluids is becoming more costly and more difficult to obtain. Operators, as well as service companies, have therefore shown a strong desire to use produced water in field operations to reduce costs. Consequently, a series of laboratory experiments have been performed to optimize the viscosity profile of fracturing fluids prepared with produced water. Preparation of polysaccharide-based fracturing fluids with produced water frequently resulted in fluids with poor viscosity profiles despite the fact that the produced water was pretreated with biocide. Furthermore, the problem could not be resolved by just adding more biocide. In a number of representative cases, the guar-based fracturing fluids, prepared with produced water and regular biocide, quickly lost their viscosity after hydration, possibly because of the degradation of the guar by the bacterial enzymes in the produced water. A new fluid stabilizer was recently invented to address the problem, and it was observed that the addition of the stabilizer dramatically extended the lifetime of the polysaccharide-based fracturing fluids prepared with produced water. The fluid stabilizer was simply added to produced water prior to mixing the polymer. The polysaccharide-based fluids prepared with the stabilizer-treated produced water showed stable viscosity profiles at both surface and bottomhole temperatures. The use of the fluid stabilizer has greatly enhanced the fluid performance and job efficiency since its initial introduction in the field in June 2008 and was implemented in about 80 successful fracturing and sand control jobs by the end of 2008. The invention and successful application of the fluid stabilizer have reduced the operating costs for the operators and service companies. At the same time, this new technology has also helped improve the environment by cutting the fresh water usage in the field. This paper will discuss the chemistry, experimental studies, and case histories. Background Oilfield produced water is a term used in the oil industry to describe the water that is produced along with the oil and/or gas, and it may contain formation water, flowback fluids, surface water, and water from any other sources. Produced water is in good contact with various environmental elements such as air, soil, formation, and contaminated water tanks, and it is therefore not surprising that produced water often contains high level of bacteria and/or bacterial enzymes as bacteria are ubiquitous in almost every habitat on Earth. Formation water usually consists of salty water that may be the ancient seawater trapped in the formation. On the other hand, produced water stored in tanks or ponds is often subjected to evaporation that can further increase the salt concentration in the water. Measured by volume, produced water is the largest waste generated during the production process, and the volume of produced water can be several times that of hydrocarbons produced (Stephenson, 1992). The potential benefit of using such produced water, if feasible, for oilfield operations is at least twofold. First, the cost related to the proper disposal of produced water can be reduced. Produced water usually contains high levels of salt and hardness as well as bacteria. Without proper treatment, produced water is environmentally hazardous. It can be, however, costly to clean up produced water following the local, state, or federal regulations. If produced water can be treated in situ and then used to prepare fracturing fluids, the operating cost is expected to decrease. Second, as large amount of fresh water is used for oilfield operations such as water flooding, subterranean fracturing, etc. (Gleick, 1994), reusing produced water can cut the consumption of fresh water that is becoming more costly and more difficult to obtain since neighboring residents and municipal and state governments are putting more restrictions on water availability from either surface or subsurface aquifers. Operators, as well as service companies, are therefore interested in using produced water to reduce operating costs and gain competitive edges.

As fresh water becomes more expensive, production and service companies have been trying to use low-quality water such as produced water. Broadly defined, produced water may include any unclean oilfield water that often contains bacteria and high salinity/hardness. Preparation of polysaccharide-based well treatment fluids with produced water frequently results in poor viscosity even when the water is pre-treated with biocides, possibly due to the polysaccharide degradation by bacterial enzymes in the water. This paper presents our continuous success in solving the produced water reusing problems, and discusses the chemistry and case histories of the treatments in North America.A new fluid stabilizer has been developed recently that dramatically extends the lifetime of polysaccharide when used in produced water containing bacteria, possibly because the stabilizer denatures bacterial enzymes. This stabilizer has made it possible to prepare a variety of treatment fluids with produced water.Since its introduction, the fluid stabilizer has brought greatly enhanced performance for the borate-crosslinked polysaccharide fracturing and sand control fluids, as reported in SPE 124212. In this paper we continue to explore the new and broader applications of the stabilizer. The polysaccharide fluids with metal crosslinker have been successfully prepared with the stabilizertreated produced water. The fluids can endure higher temperatures. At the same time, the fluid pH can go below 4, making it possible to energize the fluids with carbon dioxide. The stabilizer has also been used to treat water contaminated with high counts of bacteria, which in turn has been successfully made into crosslinked polysaccharide fluids with improved high-temperature stability.The expanded applications of this fluid stabilizer have further lowered the operating costs for the production and service companies. This new technology has also contributed to the environmental improvement by saving fresh water and recycling produced water in oilfield operations.

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