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.

fax 01-972-952-9435. AbstractA 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.

fax 01-972-952-9435. AbstractA high performance water based mud (HPWBM) system has been used successfully to address a combination of drilling challenges faced in the Middle East. Drilling problems encountered in the area typically include shale instability through pressure transmission effects, swelling clay-stone, bit balling, drill-string accretion, differential sticking over tight gas permeable sands and down-hole losses. All these challenges can be very difficult to overcome with conventional water based mud (WBM) systems and can prove very expensive in terms of lost mud, lost down-hole tools, non performance rig time, side-tracks or ultimate failure to meet well or section objectives.The HPWBM system was introduced to provide considerable improvement in WBM performance and also provide an environmentally benign alternative to oil based muds (OBM) while emulating OBM drilling performance attributes. Recent applications in the Middle East have proved that the HPWBM system can be applied as an alternative to OBM, successfully achieving the objectives of the sections while providing drilling performance comparative to OBM. This paper discusses the technical features of the HPWBM system, gives an outline of previous applications and presents detailed case histories of the more diverse applications of the system and its components in wells in the Middle East, while comparing performance to offsets drilled with conventional WBM and OBM.

The Brent field is located in the Viking Graben of the northern North Sea and produces from the Brent Formation and the deeper Statfjord Formation. Virgin reservoir datum pressure in 1976 was approximately 5,655 psi at 8,700 ft TVDSS. Pressure support was maintained until the 1998 since when reservoir pressure has been depleting at about 500 psi per year. The current datum pressure in the Brent units is approximately 1600–1700 psi. Significant lost circulation problems started to be experienced in the late 90's and a study identified the cause as the narrowing of the mud weight window as reservoir depletion gradually lowered the fracture gradient [ref 1]. Mud weights have been lowered to mitigate against the costly lost circulation events. The mud weights currently used are typically 700–900 psi less than the shale pore pressure (i.e. underbalance). Two case histories from sub-horizontal wells last year illustrated that the shales can be drilled over 900 psi underbalanced with no indication of shale failure, however, when running in liners they both hung-up where shales had collapsed. Based on this experience, the minimum mud weight for drilling the sub-horizontal reservoir sections has been set at 700 psi underbalance relative to the interbedded shale pore pressure. Reservoir depletion has reached the point where the (static) minimum mud weight for shale stability is almost equal to the fracture propagation pressure (FPP) for the reservoir sands. In the first half of 2002, 5 of the 7 wells drilled experienced lost circulation. The average losses volume per well was over 5,000 bbls with nearly 19,000 bbls being lost on one well. Of more significance is the NPT associated with the losses, this averaged over 300 hours per well. The average monetary cost of the lost time and mud volume was close to £1 MM per well. In an environment drilling low cost sidetracks, accessing reserves of 1–2 MM boe, this situation was unsustainable. A task force set about finding possible solutions to combat the lost circulation problems. After technical review, including laboratory testing, a recommendation was made for a size and concentration of graphite to be added to the OBM. In 10 field trials to date all the sections reached TD without inducing lost circulation, however, 4 of the 10 sections did experience losses when running the liner and/or circulating prior to cementing. With the addition of the graphite the average losses per well has dropped from 5,238 bbls to 621 bbls and the associated NPT has dropped from 302 hours to less than 1 hour per well. Recent field data suggest that the graphite could add approximately 1000 psi to the fracture breakdown pressure. This opens a host of possibilities for future infill drilling in depleting reservoirs. Introduction The Brent field is located 186 km northeast of the Shetland Islands in the UK North Sea and has a STOOIP of 3.8 billion stb and a GIIP of 7.5 Tscf (figure 1). The field was discovered in 1971 and was brought on production in 1976, with annual production peaking in 1984 at 410 Mbbl/d. Since the 1980s, oil production has been experiencing decline, but because of the high solution GOR (ranging from 250–980 v/v) substantial gas reserves remain, dissolved in the residual and by-passed oil. In 1992 the decision was taken to depressurise the Brent Field to recover an additional 1.5 Tscf of gas and 34 MMstb of oil, so extending the end of field life by 5–10 years. This required a £1.3 billion redevelopment of three of the four Brent platforms to install pressure facilities for low pressure operations, to reduce operating costs, to implement safety upgrades and to refurbish the facilities.

fax 01-972-952-9435. AbstractA 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.