Injectivity Aid Qualification to Field Application for Produced Water Reinjection. A North Sea Case Study

Abstract

AbstractProduced water re-injection (PWRI) for maintaining reservoir pressure and sweeping hydrocarbon towards production wells uses water separated from the produced fluids at the surface facilities which is then re-injected into the same (or possibly alternative) hydrocarbon bearing formations. In addition to the environmental benefits of PWRI, there are other potential benefits including making cost, space and weight savings through the optimization of water treatment facilities and produced water re-injection systems throughout the life of a field.Many factors influence produced water re-injection well performance. In this paper production chemistries are examined that when applied can improve PWRI effectiveness by reducing the known negative impact of the following:impact of oil in water (increasing pore saturation, binding carried over solids) back pressure induced by fractional drag within injection lines/near wellboreThe paper focuses on laboratory evaluations leading to field applications within a North Sea field where an operator had a history of injectivity decline in 4 wells believed to be taking produced water under matrix flow conditions.This paper will share the steps taken that resulted in the initial recommendation to address the reduced injectivity; Specifically, how the chemical options were evaluated via coreflood studies on reservoir core with field crude oil and synthetic produced water that led to the application of a batch treatment of mutual solvent and organic acid treatments to the three wells. Following the batch treatment, the production declined over time. Evaluation was then carried out to determine if continual injection of a chemical could be applied to reduce the near wellbore oil saturation and modify interfacial tension (IFT) such that the enhancement in injectivity could be maintained.Chemicals with a known ability to impact oil/water interfacial tension were evaluated via IFT measurement studies leading to coreflood evaluation to determine what improvement in brine permeability could be expected to be observed in a field application. The chemistry that showed the lowest effective treatment rate at 10's of ppm vs percent levels of mutual solvent was a formulation of corrosion inhibitor and non THPS iron sulfide dissolver. This product offered multiple benefits of corrosion control, reduced IFT leading to oil mobilization and relative permeability modification of the sandstone minerals such that brine permeability increased by 150% with a dose of 25 to 50ppm product applied to the produced water.Application of remediation programs via continual injection of correctly selected production chemicals that impact reservoir wettability present an opportunity for significant savings in terms of chemical cost/production downtime over batch cleaning chemical applications.