An Integrated Study to Achieve Tech-Economic Produced Water Treatment & Re-Injection Solution

Abstract This paper presents the results of an integrated study with a techno-economic solution for the treatment and re-injection of produced water (PW) in an onshore oilfield carbonate reservoir. The reservoir currently utilizes aquifer water injection for pressure maintenance, coupled with PW disposal. As PW volumes have increased over the years and disposal capacity has declined, the need for an alternative solution has become imperative. The proposed solution involves using PW for pressure maintenance, but the tightness of the reservoirs presents challenges such as potential formation damage and injectivity reduction. As a temporary solution the PW is mixed with aquifer water for reservoir pressure maintenance, aquifer water can be diluted with approximately 35% PW to enable reinjection without any treatment (1 Grutters et al., 2023). The long-term objective presented in this paper is to define PW specifications and identify required PW treatment technologies and facilities upgrade to make it suitable for re-injection (2 Lu Xianhui, 2023). Produced Water Re-injection (PWRI) specifications were defined from core flood experiments together with corrosion experiments, representing four reservoirs with permeability of 1-10, 10-100, 100-500, 500-1000 mD. Mature PW treatment technologies, both mechanical and chemical, were investigated and compared whilst considering existing facilities upgrades to enable cost-effective PWRI to meet future production targets (3 Mohammad A. Al-Ghouti et al., 2019). Critical PWRI specifications OIW and TSS ranged from 51.5 to 246 mg/L and 24 to 64 mg/L respectively, for permeability of 1-10, 10-100, 100-500, 500-1000 mD. Corrosion experiments showed that the PW satisfied both the average corrosion and pitting corrosion requirements. Induced Gas Flotation (IGF) downstream of the existing PW skimming tank was proposed to reduce OIW 40mg/L and TSS 20mg/L with chemicals dosing meeting the PWRI requirements. The CAPEX and OPEX for the existing PW facilities upgradation and new built facilities were also estimated. In order to reduce cost, the project was proposed to construct in three phases based on PW profile, with phase-1 to upgrade existing facilities. This integrated study has resulted in techno-economically feasible solutions that contribute to enhance reservoir water injection & support oil production and achieve sustainable targets by eliminating PW disposal in water aquifers.