Designing of Successful Immiscible Water Alternating Gas (IWAG) Coreflood Experiment

Abstract

Average recovery factor in offshore field under discussion is relatively moderate due to wider well spacing and poor sweeping efficiency thus leaving significant volume of oil behind in the reservoir. Timely application of EOR is therefore necessary to enhance the recovery factor to a reasonable level. Among the various EOR processes and techniques of EOR screened, studies found immiscible water-alternating gas (IWAG) injection as the most suitable and viable option for this Malaysian mature offshore oilfield. Realistic estimate of incremental oil by EOR is paramount as IWAG application involves high CAPEX and OPEX project. Therefore, representative is required to be generated in the laboratory for constructing a realistic reservoir simulation model to understand the three phase flow in porous media and support the IWAG process for full field implementation. Important parameters in this case are residual oil saturations in sequential injection of displacing fluids water and gas and trapping of gas, injection volumes and frequency of alteration. Therefore, IWAG core flooding experiments under reservoir conditions need to be performed, results quantified and parameters for hysteresis modeling established.This paper addresses the challenges and strategies of IWAG core flooding experiment performed under reservoir conditions using representative composite native cores, live reservoir oil sample, field produced gas sample and synthetic formation brine water. The laboratory injection rates are considered equivalent to the field fluid advance velocity like in any standard displacement steps. Also, gravity stable injection mode is considered to achieve the best IWAG displacement performance. These challenges and strategies are drawn from lessons learned during accomplishment from earlier IWAG core flooding experiments. The IWAG core flooding experiments were performed on composite field core samples, arranged according to Langaas method, using current field production gas with 60 mole % CO2. The composite reservoir core samples were initially saturated with live oil and irreducible formation water and then flooded with formation water and seawater to residual oil saturation at reservoir conditions. Following, waterflooding, a number of water and gas cycle slugs were injected. The displacements were conducted at pressures well below the estimated minimum miscibility pressure during these experiments. Laboratory studies and numerical simulation study conducted on the applicability of immiscible WAG injection using high CO2 content produced gas indicated that 7.0 % additional oil recovery over waterflooding period can be recovered.

Core Flooding Application in EOR WAG Implementation: The Impact of Asphaltene Precipitation and Deposition

“…However, it has been reported that some of its effects can be captured by wettability change and relative permeability shift from a water-wet to a mixed-or oil-wet system. Few technical published papers related to various EOR/IOR case studies including CO 2 gas injection, immiscible water alternating gas (IWAG), gravity-assisted simultaneous water alternating gas (GASWAG), chemical EOR (CEOR), chemical water alternating gas (CWAG), and recent carbon capture and storage (CCS) related papers from the authors of this paper are given for reference [1,[20][21][22][23][24]. To investigate the effect of asphaltene deposition on relative permeability during WAG application, dynamic experiments were designed and conducted in the core flooding system under reservoir conditions.…”

Experimental investigation of immiscible water-alternating-gas injection in ultra-high water-cut stage reservoir

“…The complexity is associated with the wetting-phase relative permeability, corresponding to the wetting-phase saturation at which flow reversal takes place (Keller et al, 1997;Blunt, 1999;Akervoll et al, 2000;DiCarlo et al, 2000;Mohammad and Blunt, 2004;Shahverdi et al, 2011;Zuo et al, 2013). The relative permeability of the three phases has implications for the dissolution and capillary trapping mechanisms, and is significant in terms of trappedgas saturation affecting the imbibition-relative permeability of the wetting phase (Khorshidian et al, 2017;Afzali et al, 2018;Long et al, 2018;Afzali et al, 2020;Rücker et al, 2020) Core flooding experiments have also been conducted to investigate the performance of WAG flooding (Kulkarni and Rao, 2005;Guo et al, 2012;Fatemi and Sohrabi, 2013;Motealleh et al, 2013;Khanifar et al, 2015;Hoare and Coll, 2018). The characteristics of the injection capacity and oil recovery performance at different injection rates, slug sizes, and gaswater ratios have been investigated using one-, two-, and threedimensional cores.…”