Clay Stabilization in Sandstones Through Adsorption of Petroleum Heavy Ends

Abstract

Adsorption of petroleum heavy ends onto clay minerals in consolidated Berea sandstone cores and in friable California sand cores results in stabilization of the clays against dispersion and subsequent migration. Berea-sandstone permeability is rendered insensitive to fresh water, and the friable sand in which clays are the primary cementing material is stabilized against failure under increased flow rates. Introduction Formation damage by means of clay dispersion and migration has been recognized as a serious threat to well productivity for more than three decades. Today, there productivity for more than three decades. Today, there are a number of chemical treatments that can prevent damage caused by formation clays under conditions of fresh waterflooding. These treatments range from aqueous solutions of hydrolyzed metal ions such as hydroxy-aluminum to hydrocarbon solutions of cationic surfactants. In general, the chemical additives interact with the clay mineral surfaces and cause significant changes in those physical chemical properties that classically lead to formation damage. This paper presents experimental evidence for a natural clay stabilization mechanism. It is based on the observation that petroleum heavy ends (primarily the asphaltenes and resins) adsorb tenaciously to clay surfaces and significantly alter the physical and chemical properties of the clay. Sandstone cores, which are properties of the clay. Sandstone cores, which are normally extremely sensitive to fresh water, are stabilized effectively by treatment with hydrocarbon solutions of petroleum heavy ends. petroleum heavy ends. Background The alteration of montmorillonite properties by adsorption of heavy ends was observed during a recent study. Physical chemical properties responsible for clay Physical chemical properties responsible for clay migration are modeled by montmorillonite and the principles are applicable to other commonly occurring clays such as kaolinite and illite. In general, it was found that adsorption of asphaltenes and resins onto the clay occurs rapidly and, to a large extent, irreversibly under near-anhydrous laboratory conditions. Factors that influence this adsorption are the exchangeable cations on the clay, the basic nitrogen components of the asphaltenes and resins, and the solvent. As a result, the clay becomes hydrophobic, has a lower cation exchange capacity, has unusual X-ray diffraction properties, and will not disperse readily in distilled water. Thus, those properties that cause particle dispersion and migration - high surface charge and structural expansibility - are altered and the clay becomes physically "passive." Since the asphaltenes and resins are insoluble in water, the interactions between them and clays is optimized at low water contents. Surface dehydration can be achieved with solvents and, therefore, the heavy ends adsorb onto clays under certain natural reservoir conditions. Therefore, it is important to determine what effect this adsorption can have on rock properties. Experimental Methods The laboratory tests in this study were conducted on freshly cut, consolidated Berea sandstone cores. The sensitivity to fresh water of Berea sandstone, which contains significant amounts of kaolinite, is well documented and this material is an excellent model system for these studies. Four-inch cores were treated in the laboratory and analyzed for water sensitivity. No attempt was made to reuse the cores once the sequence of treatment and aging was completed. JPT P. 1061