Abstract

A new water-based mud system has been 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 in order 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 often negate the benefits of their use. Conventional water-based mud (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. With consideration to reducing drilling problems such as torque and drag, stuck pipe, low rates-of-penetration and well bore 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.

Because of this, the industry has placed a great deal of importance on developing and introducing water-based alternatives to emulsion systems. This paper presents a new HPWBM that balances high performance drilling and environmental compliance.

HPWBM Performance Attributes

The "high performance" term suggests that a HPWBM will deliver a higher level of performance than is currently attainable using conventional WBM. Researchers and engineers often focus on delivering a single, specific performance attribute when designing water-based alternatives to emulsion-based muds. For example, partially hydrolyzed polyacrylamide (PHPA) polymer is an excellent additive for cuttings encapsulation; however, PHPA does not provide all of the benefits of emulsion muds. The addition of an ROP enhancer to a water-based mud may deliver drilling rates equivalent to those of an OBM/SBM; however, it is unlikely that it alone will match the overall drilling performance of emulsion muds. Silicates have successfully been used to mimic the well bore stability characteristics of an OBM; however, they do not furnish the benefits of emulsion systems in areas such as torque and drag reduction and accretion control.

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