Reaction Between Rock Matrix And Injected Fluids In Cold Lake Oil Sand —Spotential For Formation Damage

Abstract

Abstract Most in-situ recovery processes involve heating the formation and injection of large amounts of aqueous fluids. Under these conditions, mineral reactions proceed quite readily and could cause changes in reservoir properties such as porosity and permeability. Static autoclave experiments which simulated in-situ recovery conditions showed that dissolution of quartz kaolinite and dolomite, and formation of analcime, chlorite, smectite and calcite were the major mineral reactions that occur in Cold Lake oil sands. The process variables that influence these reactions were identified through statistical data analysis. Flow experiments with sand packs have demonstrated the possible deleterious influence of these hydrothermal reactions on permeability. The results of the tests compare favorably with published field pilot data. Formation damage by fines dispersion resulting in high residual oil saturations has been observed in medium to very fine grained sands. To an extent this formation damage can be minimized by an appropriate choice of process variables. On the other hand, maximization of fluid-rock interactions may be used to advantage in " thief" zones. FIGURE 1. Factorial experimental design layout and sample code. The latter indicates the experimental conditions to which the samples were subjected. B = bitumen (blank if absent); b = 0.01 m borax (blank if absent); t = 200 °C; T = 250 °C; 26 = experiment duration (days); SW = 0.1 m NaCl; FW = no NaCl. Introduction The oil sand deposits in the province of Alberta, Canada contain a vast amount of bitumen, most of which will have to be recovered by in-situ techniques. Many processes for secondary or tertiary recovery of conventional crude oil and for the in-situ recovery of bitumen from oil sands rely on the injection of large volumes of steam to heat the bitumen and thereby reduce its viscosity. The interaction between condensed steam and rock matrix may lead to a considerable degree of mineral dissolution, transport, precipitation and transformation(1,2,3). In turn, these reactions can cause significant changes in reservoir properties such as permeability and porosity(3,4). It has been said that steam injection leads to an acceleration of diagenesis(2). Consequently, much of the research on the relation between diagenetic characteristics and oil reservoir performance(5) is relevant to enhanced oil recovery as well as to in-situ recovery of bitumen. The experimental work for the present study consisted of three major parts: (a) A major experimental-statistical study was undertaken to identify the most important mineral reactions that will occur at the pressures (up to 11 MPa) and temperatures (up to 325 °C) operative during in-situ recovery of bitumen by steam injection from the major Alberta oil sand deposits and to estimate the extent to which these reactions are influenced by process conditions. A factorial experimental design was used because it provides an optimum balance between the amount of information obtained and the number of experiments required(6). Also, the availability of standard computer programs for statistical analysis greatly facilitates the interpretation of the data in terms of trends and statistical significance(7).