Clay Stabilization Agents - Their Effectiveness in High-Temperature Steam

Abstract

Laboratory data indicated that commercially available clay stabilization polymers may be beneficial in maintaining greater sustained formation permeabilities in clayey formations subjected to high-temperature steam injection. Polymers evaluated varied in high-temperature clay stabilization properties and resistance to hydrochloric acid. Result from several field applications of one polymer are included. Introduction Steaming encompasses the entire recovery spectrum involving primary, secondary, and tertiary approaches. It has been reported that oil retrieved by steam methods represents 90% of all the oil produced by current enhanced recovery techniques. Steam recovery methods often are applied in low-temperature, poorly consolidated, shallow geological laydowns which frequently are characterized by high concentrations of clay minerals. When exposed to steam, these untreated clays may cause severe matrix permeability reduction. Sometimes this loss of rock permeability is not fully recoverable. As a consequence, reservoir depletion efficiency may be reduced. Therefore, it is plausible to predict that effective clay mineral control will play a vital role in steam recovery of hydrocarbons from clay-bearing formations.Sand problems can be caused by inadequate clay control because clay minerals often serve as cementing materials in rock formations. Should the clay swell or migrate, cementation between sand grains can be damaged or destroyed, resulting in sand production. This has been reported to be a recurring problem in numerous cyclic steam (huff ‘n’ puff) wells in which the produced sand periodically must be bailed out of the wellbore. Clay Damage Mechanisms Numerous forms of clay minerals exist in subterranean strata. Their permeability damage potential is related to structure, orientation, cation exchange capacity, and geological laydown pattern along with the existing cation environment. Clays can be classified into two basic types:expanding andlow water absorbing. Smectite (montmorillonite), a three-layer clay, is considered the most expandable in the presence of water, particularly fresh or low-salinity waters similar to those associated with steaming techniques. Mixed-layer clays, containing smectite intermixed with other clays, also are classified as expandable. In addition to causing pore plugging, expanding clays can result in a release of other clay and silica fines which tend to travel within the tortuosity of the interstices until points of lodgment or bridging occur. This can result in further restriction of pore-space dimensions and lower permeability, which are synonymous with reduced withdrawal rates. Low-water-adsorbing clays (e.g., kaolinite, illite, and chlorite) are common to many shallow as well as deep formations. Although these clays can be expected to cause less damage due to expansion than smectite, other formation damage associated with water-promoted disintegration, dispersion, and migration can occur.For an excellent description of clays most common to hydrocarbon-bearing reservoirs, reference is made to a paper by Hower. JPT P. 2121＾