Oil Field Applications of Aluminum Chemistry and Experience With Aluminum-Based Drilling Fluid Additive

Abstract

Abstract Applications of aluminum chemistry to solve drilling, completion, and production problems are discussed. Field application of a more recently developed aluminum-based product demonstrated the ability of this additive to control hydration and dispersion of drill solids and to enhance borehole stability. Introduction The complexity of aluminum chemistry and diversity of aluminum compounds has resulted in creative applications to solve various aspects of drilling, completing, and producing oil and gas wells. Due to space limitations, this paper cannot provide a comprehensive treatise on the subject. Although the most commonly used aluminum compounds for drilling fluids are clays or aluminosilicate compounds, clays and clay derivatives will not be discussed. Another unambiguous application of aluminosilicate technology (cement) will not be covered. The use of other aluminum-containing compounds includes a variety of materials effective for oil field use. Aluminum, the most abundant metal (and the third most plentiful element) in the earth's crust, occurs primarily as silicates and oxides. It has afforded opportunities for numerous oil field uses. Application of aluminum chemistry for completion and production will be covered first, followed by drilling fluid applications. Recent field results of an aluminum-based shale inhibition product will be presented. Aluminum Chemistry Adaptable to Oil Field Technology The versatility of aluminum chemistry can be discussed in the context of general characteristics of this element. Aspects of aluminum chemistry featured in the following applications include:–Aluminum can exist as compounds that may be soluble or insoluble in water (Table 1) depending on the counterion and solution pH.–Aluminum ions, formed by dissolution of soluble aluminum salts, exist as hexahydrate ions in an octahedral configuration (Fig. 1). The high charge of aluminum ions results in loss of hydration shell protons that lead to a series of hydrolysis ions (Fig. 2). Aluminum induced hydrolysis produces acidic solutions for virtually all water-soluble salts.–Aluminum exhibits a complex, pH dependent chemistry in aqueous systems and the ability to produce important effects from either acidic or alkaline aluminum sources. Solutions of aluminum salts contain only Al(H2O)63+ at pH values below 3. When pH values are between three and five, aluminum species are distributed between a mixture of hydroxo species including Al(OH)2+, Al(OH)2+, and various polynuclear (containing two or more aluminum atoms) cations. At pH values between 5 and 6, Al(OH)3 appears. As the pH becomes more alkaline Al(OH)4- becomes dominant.–Under appropriate conditions aluminum forms an amphoteric hydroxide which at higher pH's forms a soluble tetrahydroxyaluminate anion (Fig. 3).–Aluminum hydroxides exist in several crystalline or amorphous forms (Fig. 4).–Multivalent aluminum possesses the ability to act as a crosslinking agent to form polymeric gels.–Metals may form chelates or heterocyclic complexes in which a metallic ion is covalently bonded by nonmetallic atoms in the same molecule. Aluminum chelation can occur by agents such as citric acid (Fig. 5) or more complex and varied structures within humic acids (Fig. 6) or lignosulfonates (Fig. 7). P. 571^