Mechanistic Modeling, Design, and Optimization of Low Salinity Waterflooding
Creators: name: Dang, Cuong Thanh Quy
Publisher: name: Graduate Studies
Year: 2015
Subjects: subject: Engineering--Petroleum
subject: Low Salinity Waterflooding
subject: Enhanced Oil Recovery
subject: Wettability Alteration
subject: Multiple Ion Exchange
subject: Geochemistry
subject: FOS: Earth and related environmental sciences
subject: Waterflooding
subject: Water-Alternating-Gas
subject: Robust Optimization

description: Low Salinity Waterflooding (LSW) is an emerging attractive enhanced oil recovery (EOR) method because of its oil recovery performance and relatively simple, environmentally friendly implementation, when compared with conventional high salinity waterflooding and EOR approaches. Most studies on the subject have focused on the experimental and theoretical work, with varying, sometimes contradictory conclusions. This dissertation presents a systematic study of the LSW process and its potential for improved oil recovery. The starting point for this research is an investigation of the underlying mechanisms of LSW by reviewing and analyzing the broad range of results that have been published over the past twenty years. Wettability alteration, leading to increased water wetness due to ion exchange and geochemical reactions, has been found to be the primary LSW mechanism. Based on the above findings, this thesis introduces one of the first mechanistic LSW models that can be used to design LSW process and interpret its laboratory and field-scale performances. A comprehensive ion-exchange model, fully coupled with geochemistry specially designed for the modeling of LSW physical phenomena, has been developed and successfully implemented in Computer Modelling Group’s GEM™ reservoir simulator. Not limited to pure LSW, it can also be used to model and design hybrid EOR LSW techniques such as Low Salinity Water-Alternating-CO2. Simulation results from new model were validated against the following: (1) PHREEQC geochemistry software; (2) North Sea sandstone coreflooding; and (3) Texas sandstone coreflooding. In these tests, validation results were excellent, in terms of average oil saturation, ion evolution and effluent pH profile. Although the advantages of LSW have been reported, none of the systematic approaches has addressed the issue of modeling and predicting LSW field-scale performance. The new modeling approach introduced in this research can effectively capture the critical effects of geology in the LSW process. This integrated modeling approach involves the use of geological software, a reservoir simulator, and a robust optimizer in a closed-loop for sensitivity analysis, history matching, optimization, and uncertainty assessment. To capture clay effects, a new empirical correlation for cation exchange capacity has been developed. A 2D geostatistical LSW model was used to investigate the effects of geology on process performance. The field-scale benefits of secondary and tertiary LSW is then proven. An important advantage of LSW is that it can be integrated with other EOR methods (in hybrid LSW processes). The merits of combining LSW with CO2 injection is investigated, and a novel EOR method, Low Salinity Water Alternating CO2 (CO2 LSWAG), is proposed. CO2 LSWAG injection promotes the synergy of the mechanisms underlying these methods which further enhances oil recovery and overcomes the late production problems frequently encountered in conventional WAG. CO2 LSWAG has been evaluated in both one-dimensional and full-field scale with positive results compared with conventional high salinity WAG. The last part of this work presents an optimization approach for LSW well placement. The optimization results show that oil recovery can be significantly increased by locating wells for optimal wettability alteration and sweep efficiency. Robust Optimization for LSW was introduced based on multiple geological realizations, which overcomes the current weakness of optimization based on single geological realization. Robust Optimization is demonstrated to be an excellent approach for reducing the effect of geological uncertainty in LSW projects. Finally, preliminary screening and implementation guidelines for LSW operation are presented for both laboratory investigation and field-scale applications.