Tannin-Based Deflocculants in High Temperature High Pressure Wells: A Comprehensive Review

Clay deflocculants that are commonly used in water-based muds under high temperature high pressure (HTHP) oilwell drilling conditions have been found to contain chromium which is toxic. Tannin-based deflocculants are regarded as a more environmentally friendly and suitable alternative to the chrome-based deflocculants. However, tannin-based deflocculants have not been studied extensively and understood completely, and for the past two years, there have not been many active pieces of research in the area. To advance research in the area, there is a need to critically and holistically review research works that have been done so far on tannin-based deflocculants as drilling mud additives to identify research challenges and opportunities. This review paper provides an overview of tannin-based deflocculants used in water-based muds under HTHP drilling conditions, including the various forms, thermal stability, deflocculating ability and environmental acceptance of the deflocculant. The review revealed that under HTHP conditions, modified and unmodified tannin-based deflocculants both deflocculate water muds well and are thermostable. However, only a few studies have been conducted on their usage as deflocculants at temperatures of 150ºC or above. The research gaps identified if pursued could advance the use of tannin-based deflocculants as green substitutes for the conventional chrome-based deflocculants.

A critical review of carbonate reservoir wettability modification during low salinity waterflooding

The nature of carbonate reservoirs promotes the adsorption of oil onto the rock surface hence making oil recovery a challenge even with the interventions of varied chemical EOR methods.Recently,low salinity water flooding has become of great interest since it is cost-effective and environmentally friendly.Although low salinity waterflooding has been highly investigated in sandstone reservoirs,it is not the same for carbonate reservoirs due to its complexities.Nonetheless,it has been proposed as a favourable technique to mobilise the trapped oil in carbonate reservoirs.Wettability alteration is regarded as the most accepted mechanism for low salinity flooding but has not been well understood making field scale applications doubtful.In this paper,we present a detailed review of the wettability alteration mechanisms in carbonate reservoirs during low salinity waterflooding.Parameters influencing wettability alteration in carbonates and the interactions that occur at the rock/brine/oil interface are also presented.The different methods utilised for wettability measurements during low salinity waterflooding are also reviewed including their drawbacks and advantages and recommendations.This will provide an improved understanding of the low salinity flooding application in carbonate reservoirs.