Summary A new, environmentally safe water-based polymer system has been developed for drilling applications with temperatures up to 232°C (450°F) and high pressures. The system components are newly developed synthetic polymers that do not contain chromium or other environmentally harmful materials. These new synthetic polymers are designed to perform specific functions at high temperatures and the innovative designs of these thermally stable polymers allow for the use of a minimum number of products in the formulation of high-temperature fluids. The new system consists of two basic polymeric components for rheology and filtration control at high temperatures. High-temperature fluid formulations are greatly simplified utilizing this new system, with only the two polymeric components being required, along with a pH control additive, weight material, and small amounts of clay for filter cake quality. This simplicity is a significant advantage over "traditional" high-temperature systems, which normally require the use of a large number of additives to control or limit the effects of thermal degradation. The new system may be formulated with fresh water or sea water, providing flexibility for a variety of drilling environments. Excellent resistance to common contaminants, such as calcium and magnesium hardness and solids accumulation, is another important characteristic of this new system. This paper will review the previous state of the art with respect to high-temperature, water-based muds and will generically discuss the unique chemistry of the newly developed polymer system components. System formulation and application will be discussed. Introduction The application of high-temperature, water-based fluids is traditionally based on concerns associated with the use of oil-based fluids, such as environmental compliance, logistical problems in remote locations, gas solubility in the fluids, and anticipated lost circulation zones. Although during the past several decades high-temperature, water-based fluids composed of modified natural products have been proven to exhibit effective and predictable performance,1 today's environmental and drilling performance requirements have mandated an alternative to these materials.2 For over 20 years sulfonated polyacrylic chemistries have been available for fluid loss control additives and fluid deflocculants. Since their inception, most of these polymers contain one, two, or three starting materials selected from a relatively small group of common monomers. High-temperature, water-based drilling fluids prepared with these materials often require supplemental treatment with modified natural products to achieve their necessary performance properties. The utilization of new and economically feasible monomers, along with a different approach to polymerization, allows for the preparation of new materials for use in high-temperature, water-based drilling fluids. In turn, these new fluids do not require traditional products to obtain good rheological and fluid loss control properties. The New High-Temperature Polymers Control of the Fluid Loss Properties of Drilling Fluids. Advances in high-temperature, high pressure (HTHP) fluid loss control have been realized with a new cross-linked copolymer prepared from acrylamide (monomer A), a sulfonated monomer (monomer S), and a cross-linking monomer (monomer X). The amount of cross-linking in the polymer's structure plays an important role in its solubility,3 which is related to the property of fluid loss control. Too much cross-linking will result in a polymer that is very rigid in physical structure and difficult to hydrate in water-based fluids. Too little cross-linking produces polymers having properties similar to those of the commonly used acrylamide copolymers, whose long and linear structures are known to have limited tolerances to contamination and shear. The new cross-linked polymer is compact and globular in morphological structure, as Fig. 1 shows. It retains a somewhat compact spherical shape in aqueous solution when compared to the expanded form of non-cross-linked linear chain polymers. When comparing the properties of this polymer to traditional linear molecules having the same molecular weight, the cross-linked polymer has a much smaller hydrodynamic volume in aqueous solution. The unique structure of the cross-linked polymer results in it being sterically hindered, increasing its intrinsic hydrolytic stability. Also, cross-linking makes it less sensitive to solids and more resistant to shear. Consequently, both rheological and filtration control properties of water-based drilling fluids are improved and preserved with the use of this unique polymer.

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With the increasing use of Managed Pressure Drilling (MPD) to mechanically control bottomhole pressures for drilling narrow mud-weight windows, little consideration has been given until recently to integrating drilling fluid design and MPD operations for a specific application. This paper describes how two converging technologies have emerged in recent years that both converge on more effectively managing narrow hydraulic operating windows in extended reach, horizontal, and through tubing drilling operations. The performance limitations of drilling fluids are discussed within the context of the drilling fluid requirements needed to drill these more critical well types and how attempts to manipulate the rheological profile have only been partially successful at balancing the need for sufficiently high enough rheology to adequately suspend dense weighting agents and the requirement for low-rheology fluids to manage downhole hydraulic needs (ECD). It is suggested that drilling-grade barite has major limitations when designing fluids for wells with critically narrow hydraulic operating windows, which are overcome by a novel process that produces micronized barite with an average particle size of less than 2 microns. By formulating treated micronized barite (TMB) in drilling fluids instead of API Barite, low-rheology drilling fluids may be formulated that enable downhole frictional pressures to be reduced by 0.5-lb/gal equivalent density with minimal risk of barite sag or settlement. Managed Pressure Drilling (MPD) is a fast emerging technology that has the ability to reduce ECD's by applying annular backpressure. The authors suggest that drilling fluids that enlarge hydraulic operating windows should be considered as one of the ‘tools’ of Managed Pressure Drilling as defined by IADC. Case histories from the Gulf of Mexico and the North Sea describe how the combination of TMB drilling fluids and MPD operations provide a powerful synergistic combination of technologies that is capable of drilling the narrowest of hydraulic operating windows. Break-circulation pressures, swab-and-surge pressures are lower and pressure transmission from downhole pressure-while-drilling (PWD) tools are more instantaneous in low-rheology fluids. This allows better control of downhole pressures, further reducing the risk of wellbore instability and lost circulation events during MPD operations. Aspects of software design that predicts ‘in time’ wellbore hydraulics by coupling downhole drilling fluid rheology to annular pressures in the absence of PWD measurements while tripping and casing are also described that further improve the capability to manage bottomhole pressures and wellbore security in critical narrow hydraulic operating windows. The authors conclude that a combination of MPD techniques and low-rheology TMB drilling fluids have the potential to drill wells that are currently considered ‘hydraulically undrillable’ by enhancing wellbore security and reducing drilling risk in extended reach, horizontal and through tubing drilling applications for development drilling and redevelopment of ‘brownfield’ reservoirs.

A new, environmentally safe water-based polymer system has been developed for drilling applications with temperatures up to 232 C (450 F) and high pressures. The system components are newly developed synthetic polymers that do not contain chromium or other environmentally harmful materials. These new synthetic polymers are designed to perform specific functions at high temperatures and the innovative designs of these thermally stable polymers allow for the use of a minimum number of products in the formulation of high-temperature fluids. The new system consists of two basic polymeric components for rheology and filtration control at high temperatures. High-temperature fluid formulations are greatly simplified utilizing this new system, with only the two polymeric components being required, along with a pH control additive, weight material, and small amounts of clay for filter cake quality. This simplicity is a significant advantage over "traditional" high-temperature systems, which normally require use of a large number of additives to control or limit the effects of thermal degradation. The new system may be formulated with fresh water or sea water, providing flexibility for a variety of drilling environments. Excellent resistance to common contaminants, such as calcium and magnesium hardness and solids accumulation, is another important characteristic of this new system. This paper will review the previous state of the art with respect to high-temperature, water-based muds and will generically discuss the unique chemistry of the newly developed polymer system components. System formulation and application will be discussed. Introduction The application of high-temperature, water-based fluids is traditionally based on concerns associated with the use of oilbased fluids, such as environmental compliance, logistical problems in remote locations, gas solubility in the fluids, and anticipated lost circulation zones. Although during the past several decades high-temperature, water-based fluids composed of modified natural products have been proven to exhibit effective and predictable performance, today's environmental and drilling performance requirements have mandated an alternative to these materials. For over 20 years sulfonated polyacrylic chemistries have been available for fluid loss control additives and fluid deflocculants. Since their inception, most of these polymers contain one, two, or three starting materials selected from a relatively small group of common monomers. High-temperature, water-based drilling fluids prepared with these materials often require supplemental treatment with modified natural products to achieve their necessary performance properties. The utilization of new and economically feasible monomers, along with a different approach to polymerization, allows for the preparation of new materials for use in high-temperature, water-based drilling fluids. In turn, these new fluids do not require traditional products to obtain good rheological and fluid loss control properties. The New High-Temperature Polymers Control of the Fluid Loss Properties of Drilling Fluids. Advances in high-temperature, high pressure (HTHP) fluid loss control have been realized with a new cross-linked copolymer prepared from acrylamide (monomer A), a sulfonated monomer (monomer S) and a cross-linking monomer (monomer X). The amount of cross-linking in the polymer's structure plays an important role in its solubility which is related to the property of fluid loss control. Too much cross-linking will result in a polymer that is very rigid in physical structure and difficult to hydrate in water-based fluids. P. 263^

In an era of increasing awareness of worker health issues one of the key concerns in exploration activities is the exposure of wellsite personnel to vapors generated by organic materials in drilling fluids. Areas on the drilling location with the highest exposure potentials are the shale shakers and mud pits. These areas are often enclosed in rooms and ventilated to prevent unhealthy levels of vapors from accumulating. In continuing efforts to minimize health risks, new products are evaluated to minimize the volatility of organic materials used in drilling fluids. This study presents a laboratory technique for measuring vapors generated from organic materials in drilling fluids. Using this technique, data will be presented comparing the volume of vapors generated from diesel oils, mineral oils, synthetic fluids and a water-miscible glycol. Field data collected from the shaker and mud pit areas of drilling operations will be used to validate the laboratory study to field conditions. The potential health effects of the collected vapors will be reviewed. Introduction A study was initiated in 1989 to determine the nature, concentration and source of vapors generated from oil-based muds. Previous studies indicated over 90% of the vapors from oil-based mud originates from the base oil.1 The initial laboratory study consisted of the evaluation of six diesel fuels and three mineral oils. The results of the initial analyses indicated that vapor generation on the rig could be predicted by laboratory analysis and that the selection of the base fluid significantly impact vapor generation. For this paper, an additional six mineral oils have been analyzed for vapor generation. Since the initial study, synthetic-based drilling fluids have begun to replace mineral oil-based muds in an effort to reduce the impact of discharges on the marine environment. Four of the synethic fluids currently in use and one experimental water miscible glycol (WMG) have also been analyzed for vapor generation using the same procedures. In addition to the laboratory analyses, field samples were collected from offshore rigs using mineral oil-based mud (OBM), polyalphaolefin (PAO) synthetic-based mud (SBM), WMG, and also from an onshore rig using diesel OBM. Methods and Materials In order to properly analyze the vapors from oils, synthetics, water miscible glycols, and the muds based on these fluids, suitable techniques for sampling, quantifying and analyzing the collected vapors had to be established. An air sample pump and coconut-based charcoal sorbent tubes were obtained from SKC Inc. The sorbent tubes contain two sections of charcoal. The function of the front section is to collect organic vapors for analysis; the function of the second section is to determine if the first section has been saturated with absorbed organics. This NIOSH/OSHA approved equipment came with a general test procedure but it was necessary to establish a suitable sample collection rate and time. A 50 mL sample of #2 diesel fuel obtained from a rig was heated to 66°C in a 250 mL beaker. The air just below the top rim of the beaker was sampled at a rate of 1 L/min. The first sample collected for 5 min produced good results with no organics seen in the second section of charcoal. The second sample collected for 10 min saturated the front section of charcoal so that organics were measured in the second section. In the initial laboratory investigation of diesel and mineral oils, a sample collection time of 5 min was used. In later analyses of low volatility mineral onils, synthetics, and water miscible glycols, the sampling period was increased to allow for detectable levels of organics to be absorbed in the first section of the sorbent tubes. Temperatures were selected to match the mud temperatures normally observed in the field at the flow line.