Direct numerical simulation of density driven fingering flow: Towards a model to predict the spacing between halite fingers in hydrocarbon reservoirs

Abstract

Halite cementation is a major exploration risk in hydrocarbon reservoirs. Halite-cemented reservoir zones are characterized by extremely low porosity and permeability due to partial or complete occlusion of the pore space. Despite being a key process that affects the quality of the productive formation, a quantitative analysis of the physical processes responsible for halite cementation is still missing in the scientific literature. Brine reflux caused by temperature and density gradients is one of the main physical mechanisms responsible for the intrusion of salt in the pores of a productive formation. Physically, the dissolution of salt by the resident brine creates a zone of higher density which may give rise to the development of flow instabilities. In this work, we present a quantitative methodology for estimating the distribution of halite-cemented zones by numerically simulating unstable flows for different flow and rock parameters. The main non-dimensional parameter, the Rayleigh number, that governs the flow is identified. The impact of the Rayleigh number on finger distribution is investigated using a statistical methodology to obtain a finger spacing distribution. Finally, a simple relationship is developed between finger spacing and the Rayleigh number that may be used to predict finger spacing.