Oil based drilling fluids and advances in drilling fluid compositions are described in applicant's co-pending application PCT CA2007/000646 filed April 18, 2007 and incorporated herein by reference. This co-pending application describes the chemistry of organoclays and primary emulsifiers for use in various applications including oil-based drilling fluids and various compositions wherein the viscosity of the compositions may be controlled.
By way of background and in the particular case of oil muds or oil-based drilling fluids, organophilic clays have been used in the past 50 years as a component of the drilling fluid to assist in creating drilling fluids having properties that enhance the drilling process. In particular, oil-based drilling fluids are used for cooling and lubrication, removal of cuttings and maintaining the well under pressure to control ingress of liquid and gas. A typical oil-based drilling mud includes an oil component (the continuous phase), a water component (the dispersed phase) and an organophilic clay (hereinafter OC) which are mixed together to form a gel (also referred to as a drilling mud or oil mud). Emulsifiers, weight agents, fluid loss additives, salts and numerous other additives may be contained or dispersed into the mud. The ability of the drilling mud to maintain viscosity and emulsion stability generally determines the quality of the drilling mud.
ER resins are "engineered resins"; the term "ER resin" or "Gilsonite ER resin", as used herein, means a purified fraction of uintaite. These fractions are substantially enriched in maltenes or asphaltenes relative to natural uintaite. Merely dissolving uintaite in a solvent in which it is soluble (i.e., a solvent that dissolves greater than about 90% of the uintaite) and filtering this solution does not produce a purified fraction of uintaite as defined herein. Such a simple filtration process does not substantially change the asphaltene to maltene ratio from that of natural uintaite. Therefore it does not produce the asphaltene-enriched and maltene-enriched purified fraction of uintaite useful in this invention.
The term "maltene", as used herein, refers to the fraction of uintaite that is dissolved when finely ground uintaite is contacted with 20 volumes of hot heptane at 80 solution is filtered through a 0.8 micron filter. Maltene-enriched fractions of uintaite, such as ER-140 and ER-115, have a weight ratio of maltenes to asphaltenes of greater than about 6; preferably greater than about 15; most preferably these resins are substantially free of asphaltenes, i.e., less than 2 wt. % asphaltenes. Moreover these resins are also substantially free of ash.
Maltene-enriched ER resins as defined herein have softening points below about 140 relative to natural uintaite; they have at least 50% fewer asphaltenes than natural uintaite, preferably at least 75% fewer, and more preferably at least 90% fewer. These maltene-enriched ER resins also have reduced mineral-derived insolubles, i.e., ash. These insolubles are below 0.1% by weight, preferably below 0.05%. The maltene-enriched fractions of uintaite useful in this invention comprise at least 60% maltenes, preferably at least 80% maltenes and most preferably at least 90% maltenes. Maltene-enriched ER resins have lower softening points than those of natural uintaite. Solution viscosity, viscosity stability and melt viscosity are also substantially improved over available grades of natural uintaite. The less soluble, high melting, asphaltene-enriched fractions are also called ER resins.
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