The use of salts, such as potassium chloride (KCl) and sodium chloride (NaCl), as temporary clay stabilizers during oil well drilling, completions and servicing has been in practice for many years. Their effectiveness in this practice has been well established throughout the industry. However, because of the bulk and potential environmental hazards associated with the salts, many operators have begun to search out alternatives to their use.
Recent research has developed a relationship between physical properties of various cations (K+Na+, etc.) and their efficiency as temporary clay stabilizers. These physical properties were then utilized to synthesize an organic cation with a higher efficiency as a clay stabilizer than the typical salts now used in the oil industry. This allows much lower salt concentrations to be used to obtain the same clay stabilizing effectiveness. The liquid product has proven to be much easier to handle and transport. It has been shown to be en environmentally compatible and is biodegradable in its diluted form. Its effectiveness in fracturing operations has been extensively proven in numerous treatments in various formations throughout the U. S. and Canada.
References and illustrations at end of paper.
Most oil and gas producing formations contain clay minerals that were either originally deposited during sedimentation (detrital clay), or formed later by the action of heat, pressure and time on minerals already present or precipitated from fluids flowing through the matrix (authigenic clay). The importance of these minerals in the production of oil and gas and the potential permeability damage they can cause have been widely investigated.1–3 The two major mechanisms by which these minerals can cause permeability damage are swelling and by migration. In swelling, clay imbibes water into its crystalline structure and subsequently increases in volume, plugging the pore in which it resides. In migration, clay minerals can be dispersed by contact with a foreign fluid, or can be entrained by produced fluids and transported until a restriction is encountered (usually a pore throat) where the entrained panicles bridge, forming a restriction in the capillary. The mechanisms of migration of clays and other fine minerals have also been extensively explored.4–6
Clay stabilizing additives can be grouped into two basic categories; temporary or permanent. Temporary clay stabilizers are those that prevent clay swell and migration during drilling, completion, or servicing of an oil/gas well. The treatment can be easily removed by produced fluids following the treatment. Until now, all temporary clay stabilizers were salts, such as potassium chloride (KCl) or sodium chloride (NaCl). Permanent clay stabilizers are additives used in conjunction with temporary clay stabilizers. These are usually cationic organic polymers that tightly bound to the clay surfaces and are not moved by produced fluids.7,8 Most advances in clay treatment made in the last 15 years have been in the use of permanent clay stabilizing additives.
Recently a number of factors have prompted the investigation of temporary clay stabilizers. The primary factors have been (1) the difficulty in handling and mixing large quantities of salts, especially in massive fracturing operations and (2) increased concern with the disposal of unused salt water and produced fracturing water.
