Abstract

Wettability has a significant effect on hydrocarbon recovery from all types of reservoirs. Each reservoir has a wettability state that leads to maximum recovery, but the initial wettability of a reservoir is usually not optimal. Traditionally, we have used surfactants and chemical agents to try and optimize wettability and recovery, but this process is expensive and does not always produce the desired results. This talk will outline the state of the science in wettability, as well as a methodology to realize the goal of maximum recovery.

This methodology changes wettability by changing water chemistry. This technique can be employed during normal waterflood operations in conventional fields, or during hydraulic fracturing and completions in unconventional targets. This technique has several advantages including substantially lower costs, ease of application and lower probability of negative outcomes. The successful approach to wettability alteration requires several key steps: screening the fields to identify good candidates, simple laboratory techniques to evaluate the increased recovery potential, economic evaluations to estimate costs and benefits, and finally, well-constrained geochemical models to help design the wettability-modifying fluids.

Examples from the Permian basin using the methodology described are presented. These include formations such as the Spraberry, Avalon and Bone Springs. In conventional reservoirs that have favorable conditions incremental recoveries between 5 to 15% OOIP are possible and given the relatively low CAPEX and OPEX many cases will be profitable. The application of this technique to unconventional resources is still being explored, but offers the opportunity to increase initial flow rates and extend decline curves. While some current assumptions will be refined as we become more knowledgeable, the basic idea, that we can alter wettability with water chemistry to optimize recovery seems well justified.