The influence of individual clay minerals on formation damage of reservoir sandstones: a critical review with some new insights

Abstract

The influence of individual clay minerals on formation damage of reservoir sandstones is reviewed, mainly through the mechanism of fine particle dispersion and migration leading to the accumulation and blockage of pore throats and significant reduction of permeability. The minerals discussed belong to the smectite, kaolinite, illite and chlorite groups respectively. These minerals usually occur in an aggregate form in reservoir sandstones and the physicochemical properties of these aggregates are reviewed in order to reach a better understanding of the factors that lead to their dispersion in aqueous pore fluids. Particularly significant properties include the surface charge on both basal and edge faces of the clay minerals and how this varies with pH, external surface area of both swelling and non-swelling clays, porosity and pore size distribution in the micro- and meso-pore size range and overall aggregate morphology. For non-swelling clays, and perhaps even for swelling clays, dispersion is thought to be initiated at the micro- or meso-pore level, where the interaction between the pore solution and the charged clay surfaces exposed on adjacent sides of slit- or wedge-shaped pores brings about expansion of the diffuse double electric layer (DDL) and an increase in hydration pressure. Such expansion occurs only in dilute electrolyte solutions in contrast to the effect of concentrated solutions which would shrink the thickness of the DDL and so inhibit dispersion. Stable dispersions are formed, particularly where the solution pH exceeds the isoelectric pH of the mineral, which is often at alkali pH values, so that both basal face and edge surfaces are negatively charged and the particles repel each other. The osmotic swelling of smectitic clays to a gel-like form, so effectively blocking pores in situ, is often invoked as an explanation of formation damage in reservoir sandstones. Such swelling certainly occurs in dilute aqueous solutions under earth surface conditions but it is uncertain that stable smectitic gels could form at the temperatures and pressures associated with deeply buried reservoir sandstones.

Wetting Effects and Molecular Adsorption at Hydrated Kaolinite Clay Mineral Surfaces

“…Clay minerals, along with quartz, often form surface coatings in the pores of sandstone reservoirs, 5 as can be seen from scanning electron and atomic force microscopy for example, Figure 1. Illites, smectites, illite-smectites mixed layers and kaolinites are amongst the most abundant types of clay mineral found within sandstone reservoirs, 5 and whilst illites and smectites are generally considered as water-wetting, kaolinite is considered to be oilwetting.…”

“…Illites, smectites, illite-smectites mixed layers and kaolinites are amongst the most abundant types of clay mineral found within sandstone reservoirs, 5 and whilst illites and smectites are generally considered as water-wetting, kaolinite is considered to be oilwetting. 4 Figure 1: Electron scanning microscope image (left) of a sandstone core presenting a composition of large quartz grains (silver), pore water (blue) and clay minerals between quartz grains (grey and brown).…”

“…When aluminum becomes incorporated in the structure, aluminosilicate minerals form, including the cation exchange mineral families: zeolites and clay minerals. 5 As a result of their high surface area and cation exchange properties, these minerals, whether from natural deposits or synthetic analogues, have found multiple practical applications and have been extensively studied using both analytical laboratory based techniques as well as molecular simulations. [6][7][8] The surfaces of both zeolite and clay minerals present an interesting contrast to silicate minerals as surface bound exposed cations possess a large enthalpy of hydration and (depending on the cation) present water wetting domains, where as the silicate domains behave more akin to quartz, with hydrophobic properties.…”

Exceptional reservoir quality in HPHT reservoir settings: Examples from the Skagerrak Formation of the Heron Cluster, North Sea, UK

“…Intact chlorite coatings provide an effective barrier for potential quartz crystal growth from the detrital surface into the pore space, due to the high crystal interconnection (Pittman et al, 1992;Ajdukiewicz and Larese, 2012;Haile et al, 2015). Illite coatings on the other hand are in respect to chlorite coatings less able to prevent quartz outgrowth due to the normally oriented, fibrous crystals and the low degree of crystal interconnection (Guven et al, 1980;Storvoll et al, 2002;Wilson et al, 2014). The mixed clay coatings in the Egret field have a very high surface coverage (>85%; Fig.…”

Carbonate cementation in Upper Eocene clastic reservoir rocks from the North Alpine Foreland Basin (Austria)

“…According to the constant high pH, which is buffered by feldspar dissolution, and the concentration of cations dissolved in the pore water during the eogenesis of Eocene sandstones, the formation of 2:1 clay type smectite was favored (e.g. Kerr, 1952;Hurst & Irwin, 1982;Wilson et al, 2014). Eogenetic kaolinite formed + by feldspar disintegration in absence of K .…”