In an industry where the technical demands on a drilling fluid are ever increasing, the use of invert emulsion fluids has been seen as a necessity to meet required drilling performance criteria. At the same time there is increasing pressure to comply, and even exceed, the tightening environmental demands on our industry which has made the use and associated waste treatment of these invert fluids complex and costly. A drilling fluid, which has the drilling performance characteristics of an invert emulsion fluid, but can exhibit the benign environmental characteristics of a simple water-based fluid, has long been the goal of fluids development. This paper describes the development and application of a unique water-based fluid that utilizes a triple inhibition approach to delivering invert emulsion-like drilling performance. Each component of the fluid system has also been designed to ensure compliance with some of the world's most demanding environmental requirements. The resulting fluid is flexible in formulation such that it can be utilized in freshwater on land wells to meet chloride discharge requirements, can be formulated in seawater for shelf wells to meet low toxicity and logistics requirements, and can be formulated in saturated salt water to meet toxicity and performance requirements for deepwater environments. The applications of this fluid on a global basis will be evaluated, comparing the drilling performance and economics to offset wells which have utilized both conventional water-based fluids and invert emulsion fluids. Introduction Invert emulsion drilling fluids, also known as "oil-based muds" (OBM) and synthetic-based muds (SBM), have traditionally always been the fluids of choice when drilling demanding wells that required a fluid that ensured a high degree of wellbore stability, was capable of insuring high rate of penetration (ROP), gave good lubricity and demonstrated the lowest potential for stuck pipe. The development of a water-based drilling fluid which could exhibit similar drilling characteristics tod an invert emulsion drilling fluid has long been seen as the ultimate goal of drilling fluids research and development. Invert emulsion drilling fluids (OBM) are universally recognized as being the most efficient fluids to drill with due to the absence of contact between the drilled formations and water, and due to the inherent oil wetting and lubricity characteristics of these fluids. The advantages of invert emulsion drilling fluids have been well documented. The major advantages are:Improved wellbore stabilityHigh degree of contamination toleranceImproved rate of penetrationLow coefficient of frictionThin, lubricated filter cakeLow dilution rates and ease of engineeringHigh degree of re-usability The disadvantages of invert emulsion drilling fluids are typically outweighed by the advantages and have similarly been well documented. The major disadvantages are:Poor environmental characteristicsPoor fracture sealing behavior (higher losses)Density sensitive to temperature/pressureGas solubilityHigh unit costLogistical issues with bulk fluid transfers Several water-based drilling fluid systems have been developed over the past decade that have began to close in on the goal of OBM-like drilling performance.[1–9] A few of the more successful WBMs have been:Potassium/salt/glycol fluidsSilicate gluidsCaCl2/polymer fluidsCationic fluids

In the last years the quest for hydrocarbons findings moved into extreme drilling condition, such as ultra-deep waters, ultra-high temperatures and drilling fluids densities. Adding to these the very narrow density windows (reservoirs with very low differential fracture pressure - pore pressure), both operators and drilling fluids service companies faces increased challenges to deliver the well for production. It is common that for such applications the bottom-hole static temperature is over 180°C/356°F, even reaching temperatures in excess of 250°C/482°F in some fields, acid gases (CO2, H2S) are also present, so the list of challenges is formidable. In this paper, the authors details the common challenges for such extreme conditions wells and best practices, present a new generation synthetic-based fluid capable to withstand temperatures in excess of 500°F/260°C, as well as a unique hydraulics engineering calculations software which enable real time equivalent-circulation density (ECD) calculations. The design and development of the mew ultra-high temperature mud system is presented and its components. At the core of the system it is a new amine-free emulsifier, which is stable to temperature above 300°C/572°F. In addition, the authors will present the extensive lab work required to optimize the formulation for high densities and extreme high temperatures, detailing also the critical fluids engineering guidelines for drilling in such harsh conditions. Using laboratory, field, and computer data, the authors will demonstrate the effectiveness of the new fluid in delivering optimum drilling in extreme HTHP conditions. Also, it is illustrated how the rheology is maintained at minimum level with a micron-size weighting material, and the engineering software used for pre-planning and while drilling to accurately calculate the ECD and maintain it within the required range.

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Offshore Dubai is a maturing oil province and to access outlying, isolated hydrocarbon reserves it is necessary to expose several unstable sections of troublesome shale during drilling operations. Historically during the drilling of these wells, wellbore time-based instability issues have been experienced in the Aruma and Laffan shales on offset wells with shorter buildup sections. It is therefore necessary to drill these sections as efficiently as possible, minimizing the time these shales are exposed. Dubai Petroleum looked at a combination of new technologies available in the market that could help both to optimize the drilling of these sections and to meet the directional objectives. To control the shales a high-performance water-based mud (HPWBM) system with triple inhibition was proposed to Dubai Petroleum after a series of tests and field experience in the region. To achieve the directional objectives and minimize the time to drill the section, a performance drilling system (rotary steerable tool in combination with a modular motor) and drilling dynamics sub were suggested. The section was drilled safely in a single run with all drilling objectives achieved and breaking all previous 24-hr ROP drilling records for an offshore Dubai Petroleum well. No shale instability issues were experienced, including the longest Aruma shale section ever drilled by Dubai Petroleum. The combination of new technologies and detailed planning applied offshore Dubai for the first time allowed a step change in the Dubai Petroleum offshore drilling and enable previously inaccessible hydrocarbon reserves to be reached and produced. Introduction Geological and geophysical subsurface studies had indicated the potential of isolated, unrecovered hydrocarbon reserves offshore Dubai which could not be accessed by standard sidetrack operation. In the past decade mostly sidetracks of exisiting wells had been drilled to enhance production, prior to the drilling of a horizontal section within the reservoir. Typically a build section was drilled and the well landed in the top of the main carbonate reservoir of the Ilam and Mishrif, with the build section then cased off and a horizontal section then drilled, completed, stimulated and produced. To develop the above-mentioned isolated reserves a cost comparison between a "new drill" versus a "semi-extended reach well" was carried out. This comparison concluded that a semi-extended reach well would be more viable and less costly than a new drill. To meet the given target requirements it was necessary to drill a build section in excess of 6,800-ft (2,073-m) with approximately 4,000 ft (1,219 m) of Aruma shale and 340 ft (104 m) of Laffan shales at 76-degree inclination. Historically during the drilling offset wells, they exhibited time-dependent wellbore instability issues. Dubai Petroleum looked at new technologies available in the market that could be used to help both optimize the drilling of these sections and also to meet the directional objectives. For controlling the shales a high-performance water-based mud (HPWBM) system with triple inhibition was introduced to Dubai Petroleum. To achieve the directional objectives and minimize the time to drill the section, a performance drilling system (rotary steerable tool in combination with a modular motor) and drilling dynamics sub were utilised.