Produced-Water-Reinjection Design and Uncertainties Assessment

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This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 165138, ’Produced-Water-Reinjection Design and Uncertainty Assessment,’ by Jalel Ochi, Dominique Dexheimer, and Vincent Corpel, Total EP France, prepared for the 2013 SPE European Formation Damage Conference and Exhibition, Noordwijk, the Netherlands, 5-7 June. The paper has not been peer reviewed. Produced-water reinjection (PWR) is an important strategy for deriving value from waste water, but its implementation can face challenges related to injectivity and safety issues. The first objective of a PWRI-design study is to supply water-quality specifications, and the second is to supply injection-pressure specifications. The objective of this paper is to detail how water quality and injection pressure are deduced when uncertainties of input data are considered. Introduction Before any PWRI design commences, a feasibility study is performed to assess any compatibility issues and evaluate the risk of scaling and souring and the viability of the project. Bacteria growth and corrosion of the installations have to be tackled and mitigated upstream in the early phase of the project. The first objective of a PWRI-design study is to determine the water quality in terms of optimum total-suspended-solid (TSS) and oil-in-water (OIW) contents, which could remain in the water after treatment and which would enable maintaining the injectivity under PWRI during the field life. These two parameters allow design of the water-treatment installations. The second objective is to determine the pressure needed to achieve PWRI sustainability; the pump power and the injection-network size will be designed on the basis of this pressure. PWRI-Design Approaches There are three main approaches to PWRI design. The first approach is based on analogs and correlation laws, the second is based on laboratory experiments, and the third uses simulations with predictive models. Of these, the most effective is that of running simulations with predictive models, because this allows simultaneous determination of the water quality and the injection pressure needed to sustain injectivity. Field evidence indicates that, whatever the quality of produced waters, PWRI in matrix (or radial injection) regimes inexorably leads to a continuous decline of injectivity. PWRI is viable only in a fractured regime, and pressure and water quality have to be designed for long-term efficiency of this regime. Fractured injection, though a complex process to model, is now considered to be a part of the PWRI strategy for field developments. New PWRI simulators are based on modules describing the flow in both matrix and fractured regimes coupled with a module describing the plugging inside and around the well, as well as plugging within and around the fracture, if any. Compared with conventional fracture software used for stimulation jobs, the fracture module takes into account the thermal and poroelastic effects generated by the high leakoff of cool water.