The oil and gas industries have used “drilling muds” or drilling fluids for a considerable number of years to tap subterranean deposits of natural resources. These drilling fluids are pumped under pressure, from tanks at the wellhead, through the inside of the drill pipe. At the bottom of the bore hole, the fluid exits through openings in the drill bit. The fluid then returns to the surface through the annular space between the drill string and wall of the bore hole (or wall of the casing, where it has been put in place). Upon reaching the wellhead, the fluid is usually subjected to a number of treatments to remove gases and/or solids (e.g., drill cuttings, sand, and colloidal material), prior to recirculation of some or all of the drilling fluid.
Drilling fluids provide several important functions, including cooling and lubricating the drill bit, establishing a fluid counterpressure to prevent high-pressure oil, gas, and/or water formation fluids from entering the well prematurely, and hindering the collapse of the uncased wellbore. Drilling muds also remove drill cuttings from the drilling area and transport them to the surface where they can be separated.
As the total reserves of oil diminish, it has become necessary to drill in areas which were previously inaccessible due to technological or economic difficulties. This has led to the widespread use of oil based drilling fluids, which offer greater thermal and chemical stability than water based fluids and therefore allow drilling at extended depths and in other demanding services, such as those involving exposure to high electrolyte concentrations and soluble gases. For example, oil based drilling fluids have been used successfully in drilling hot (e.g., greater than about 150° C. (300° F.)) formations as well as those containing hydrogen sulfide. Also, to maximize recovery from each platform in offshore drilling, oil based fluids are favored due to their effectiveness for drilling deviated (i.e., angled) wells. In particular, the high lubricity of oil based fluids is necessary because of the increased torques required in deviated drilling.
The nature of oil based muds (and particularly emulsion muds) and their use to minimize high temperature gellation, contamination (e.g., by gypsum and cement), and other problems have been described, for example, by Simpson, et al. J. PET. TECH., p. 1177 (December 1961). Oil based fluids are also applicable to the drilling of clays and shales (such as those found in Western Canada) for which water-based drilling fluids are unsuitable due to heaving or sloughing caused by water imbibition into these permeable formations. In general, oil based drilling fluids are adaptable to a wide variety of formation types and wellbore conditions. Low maintenance costs as well as the ability to recycle oil-based muds contribute to their economic justification.
In contrast to true oil muds, which contain only a small amount of water, invert emulsion drilling fluids commonly contain at least 5%, up to as much as 50%, by volume of water. The water is dispersed in invert emulsions as aqueous droplets throughout a continuous (i.e., external) oil or synthetic oil phase, which may contain diesel fuel or other liquid hydrocarbon mixtures (e.g., olefinic and/or paraffinic species in the C16-C18 range). The aqueous dispersed (i.e., internal) phase is normally a saline, aqueous solution (e.g., a chloride containing brine solution, such as a 30% calcium chloride brine).
Invert emulsion drilling fluids typically result from the blending of a hydrocarbon oil with water or brine under high shear conditions and in the presence of a suitable emulsifier. Emulsification is complete when there is no distinct layer of water in the fluid. The emulsifier is required not only to form a stable dispersion of water droplets in the oil phase, but also to maintain any solids such as weighting material additives (e.g., barites) or drill cuttings in an oil-wet state. Besides these weighting materials, solid additives that are often incorporated into invert emulsion systems include organoclays and other materials that increase fluid viscosity, reduce fluid loss to the surrounding formation, and/or help suspend drill cuttings. Other additives include those which improve filtration control, hinder wellbore collapse, increase oil-wetting of solids, provide temperature stability, develop gel strength, and/or control rheology.
With respect to emulsifiers and other additives used in invert emulsion drilling fluids, various liquid and solid formulations are described in the art. For example, U.S. Pat. No. 2,946,746 describes water-in-oil type emulsions comprising a polyamide emulsifying agent which may be prepared by reacting a polyethylene polyamine with a monobasic fatty acid in sufficient quantity to react with all of the amino groups of the polyethylene polyamine, thereby converting them to fatty acid amide groups.
U.S. Pat. No. 4,233,162 describes an emulsifier composition comprising a fatty acid amide, oleic acid, dimerized oleic acid, and a surfactant dispersant that may be a mixture of a second type of fatty acid amide and a waste lignin liquor derived from pulping wood.
U.S. Pat. No. 4,374,737 describes a drilling fluid composition that uses a nonpolluting oil (e.g., vegetable or mineral oil) and a concentrate that is added in an amount of about 3% by weight. The concentrate consists essentially of a diethanolamide, a tall oil fatty acid, and an imidazoline/amide mixture. Water may be added to the composition to provide an invert emulsion system.
U.S. Pat. No. 4,508,628 describes an invert oil emulsion drilling fluid containing a non-toxic biodegradable oil, an aqueous phase, and an emulsifier. The drilling fluid has defined characteristics which provide low viscosity at the high shear rates imparted to the fluid during drilling.
WO 89/11516 describes an oil based well working fluid comprising a hydrocarbon drilling oil in combination with a sodium, calcium, or magnesium brine. The emulsifier used comprises the reaction product of an amide-amine or a hydroxyalkyl amide with a dicarboxylic acid or an acid anhydride.
U.S. Pat. Nos. 4,956,104; 5,045,593; and related patents describe the use of organophilic derivatives of water soluble polymers, prepared by reacting the polymer with a phosphatide such as lecithin, as fluid loss additives for oil based well working fluids.
U.S. Pat. No. 5,096,883 describes a non-toxic drilling fluid which can be an emulsion of a base oil, an aqueous phase, and an emulsifying agent. The base oil consists essentially of branched-chain paraffins, which may contain ester functionalities, and has a number of defined properties. The drilling fluid avoids the use of aromatics, which are said to have potential environmental consequences.
U.S. Pat. No. 6,461,999 describes the use of lubricating additives for drilling fluids which avoid the need for certain undesirable emulsifiers, surfactants, solvents, or dispersants. The additives are prepared by steam jet cooking a mixture of starch, water, and a lubricant such as a polyalkylene.
U.S. Pat. No. 6,620,770 and related U.S. Patent Application Publication Nos. 2004/0171498; 2005/0137093; and 2005/0037929 describe emulsion stability and filtration control additives for invert emulsion drilling fluids. The additives are prepared by blending a carboxylic acid terminated polyamide with the Diels-Alder reaction product of dienophiles (e.g., carboxylic acids, polycarboxylic acids, or acid anhydrides) and a mixture of fatty acids and resin acids.
There is an ongoing need in the art for emulsifier compositions having desirable emulsifying properties for invert emulsions used for oil well drilling. With space at some well sites limited, such as on offshore platforms, and with increasing costs of transport of materials to a well site, there is industry wide interest particularly in drilling fluid compositions which can be formulated and maintained (i.e., stored) with minimal or fewer quantities of solvent and other additives, compared to prior art compositions.