Summary A new water-based mud system was successfully introduced as a high-performance, environmentally compliant alternative to oil and synthetic emulsion-based muds (OBM/SBM). Historically, emulsion muds have been the systems of choice when drilling challenging onshore, continental shelf, and deepwater wells to minimize risk, maximize drilling performance, and reduce costs. However, environmental constraints, a high frequency of lost circulation, and the high unit cost of emulsion systems sometimes negate the benefits of their use. Conventional water-based muds (WBM) offer the benefits of environmental compliance, attractive logistics, and a relatively low unit cost but consistently fail to approach the drilling performance of OBM and SBM. The new high-performance, water-based mud (HPWBM) is designed to close the significant drilling performance gap between conventional WBM and emulsion-based mud systems. The system has undergone extensive field testing on very challenging onshore, deepwater, and continental shelf wells that would otherwise have been drilled with oil or synthetic-based muds. This paper provides a detailed, technical overview of the new system, discusses its inherent environmental advantages, and presents case histories comparing performance to offset wells drilled with emulsion and conventional WBM systems. Introduction The industry is increasingly drilling more technically challenging and difficult wells. Exploration and development operations have expanded globally as the economics of exploring and producing for oil and gas have improved with advancements in drilling technology. Advanced drilling operations such as deep shelf, extended reach, horizontal, and deepwater are technically challenging, inherently risky, and expensive. OBM and SBM have many inherent advantages over water-based drilling fluids, including temperature stability, tolerance to contamination, and corrosion protection. However, the fluid attributes of concern in this discussion are those most directly related to drilling performance and environmental issues. With consideration to reducing drilling problems such as torque and drag, stuck pipe, low rates-of-penetration, and wellbore stability, these wells are generally drilled with emulsion-based muds. Environmental legislation governing drilling waste is continually restricting the discharge limits of spent muds and drilled cuttings. Operators are challenged with achieving a balance between minimizing the potential environmental impact of the drilling fluid against drilling objectives. The inherent advantages provided by emulsion muds are increasingly being offset by environmental compliance restrictions.

The degree of difficulty and costs of oil and gas wells have continually increased over the past decade. Development operations continue as the economics of exploring and producing for oil and gas have improved with advancements in drilling technology. Advanced drilling technologies such as rotary stearable assemblies, logging-while-drilling (LWD) tools, annular pressure subs and new bit designs have improved the economics of performance-driven wells. With consideration of reducing drilling problems such as torque and drag, stuck pipe, low rates-of-penetration, depleted sands and well bore stability; these wells are generally drilled with non-aqueous fluids (NAF). However, the inherent advantages provided by NAF are increasingly being offset by environmental risks and liabilities. The paper discusses key criteria to be considered when selecting high performance fluids (HPF) for performance-driven wells.Performance-driven wells are classified as wells that are technically challenging and inherently risky and costly.These types of wells demand the use of HPF to contain costs and deliver well objectives. Additionally, a new high-performance water-based mud (HPWBM) has been developed and field tested as a technically competent and environmentally compliant alternative to NAF on performance-driven wells.Through a process of product substitution, ChevronTexaco has achieved project objectives while improving the environmental impact of using HPF. Introduction The industry is increasingly drilling more technically challenging and difficult wells.Exploration and development operations have expanded globally as the economics of exploring and producing for oil and gas have improved with advancements in drilling technology. Advanced drilling operations such as deep shelf, extended reach, horizontal and deepwater are technically challenging, inherently risky and expensive. Environmental legislation governing drilling waste is continually restricting the discharge limits of spent muds and drilled cuttings.Operators are challenged with achieving a balance between minimizing the potential environmental impact of the drilling fluid against drilling objectives.The inherent advantages provided by NAF are increasingly being offset by environmental compliance restrictions. The drilling process generates large volumes of drilled cuttings and waste muds.Beginning in the late 1970's it became evident that waste discharges from drilling operations could have undesirable effects on the marine ecology.1The United States Environmental Protection Agency (EPA) adopted national discharge standards for the oil and gas industries in 1993 that established restriction on oily sheens and aquatic toxicity testing for waste discharges.The American Petroleum Institute estimates that about 150 million barrels of drilling waste were generated in 1995 from onshore wells in the United States alone. Operators have used a variety of methods for managing drilling wastes, typically driven by governmental regulations and cost considerations.Three options exist to manage offshore wastes from drilled cuttings and spent drilling fluid: marine discharge, down hole injection, and onshore disposal.2All options have advantages and disadvantages with regard to total life cycle environmental impact, safety, cost, and operational performance. The environmental impact of discharging cuttings and spent water-based mud (WBM) is minimal; however, the waste from certain types of NAF can create impaired zones in the proximity of drilling operations.Currently, most synthetic-based mud (SBM) drilled cuttings can be discharged into marine waters, however, SBM whole mud discharge is not allowed.WBM whole mud and cuttings can be discharged provided the fluid meets aquatic toxicity standards.From an environmental perspective, the worst case is oil-based mud (OBM).Wells using OBM are categorized as "zero discharge" and there can be no discharge of cuttings or whole mud.All OBM-contaminated waste must be transported onshore for disposal or be injected underground at the well site.

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