Impact of Injection Water Quality on Injectivity – A Lab Study

Abstract

Waterflooding is commonly performed in oil wells for pressure support and increased oil production. Different sources of injection water can be used for waterflooding, such as aquifer water, seawater or produced water. Each of these water sources contain particulates in them that deposit at the injection point forming both an external filter cake on the reservoir face and an internal cake inside the rock surface. The properties of the external and internal filter cake negatively affect injectivity. In order to identify the optimum water filtration specs prior to injection, the contribution of different solid particle types present in the injected water on filter cake properties and injectivity need to be understood. A lab study has been undertaken to gauge the contribution of different solid types, solid sizes, and the presence of oil droplets on filter cake properties and water injectivity. The solid types tested were silica/quartz, clay, iron oxide, barium sulfate and calcium carbonate, with and without oil contamination. Membrane tests were conducted to understand the correlation between the porosity and the permeability of the external filter cake that forms at the formation face for each particulate type. A heavy slurry of selected solid particulate was mixed in brine and was compressed into a membrane under different applied pressures, and the porosity and the permeability of the cake was calculated at each stage. Core tests were designed to look at the combined effects of the external and internal filter cake on reduction in injectivity. Outcrop cores, representative of the field cores, with similar pore throat size, porosity and permeability were used in the core tests, as particle bridging at pore throats is a function of the comparison between the injected particle size and the pore throat size distribution of the reservoir. A slurry of the selected solid particulates in brine was injected into the core system and the permeability drop across the core was monitored as a function of injected water pore volumes. Both types of tests were repeated in the presence of oil contamination in the injected water. The test data from the membrane tests and the core tests were used in the numerical model to obtain the permeability reduction function for the internal and external filter cake.