Over the last few years, ADNOC has systematically investigated a new polymer-based EOR scheme to improve sweep efficiency in high temperature and high salinity (HTHS) carbonate reservoirs in Abu Dhabi (Masalmeh et al., 2014). Consequently, ADNOC has developed a thorough de-risking program for the new EOR concept in these carbonate reservoirs. The de-risking program includes extensive laboratory experimental studies and field injectivity tests to ensure that the selected polymer can be propagated in the target reservoirs. A new polymer with high 2-acrylamido-tertiary-butyl sulfonic acid (ATBS) content was identified, based on extensive laboratory studies (Masalmeh, et al., 2019, Dupuis, et al., 2017, Jouenne 2020), and an initial polymer injectivity test (PIT) was conducted in 2019 at 250°F and salinity >200,000 ppm, with low H2S content (Rachapudi, et al., 2020, Leon and Masalmeh, 2021). The next step for ADNOC was to extend polymer application to harsher field conditions, including higher H2S content. Accordingly, a PIT was designed in preparation for a multi-well pilot This paper presents ADNOC's follow-up PIT, which expands the envelope of polymer flooding to dissolve H2S concentrations of 20 - 40 ppm to confirm injectivity at representative field conditions and in situ polymer performance. The PIT was executed over five months, from February 2021 to July 2021, followed by a chase water flood that will run until December 2021. A total of 108,392 barrels of polymer solution were successfully injected during the PIT. The extensive dataset acquired was used to assess injectivity and in-depth mobility reduction associated with the new polymer. Preliminary results from the PIT suggest that all key performance indicators have been achieved, with a predictable viscosity yield and good injectivity at target rates, consistent with the laboratory data. The use of a down-hole shut-in tool (DHSIT) to acquire pressure fall-off (PFO) data clarified the near-wellbore behaviour of the polymer and allowed optimisation of the PIT programme. This paper assesses the importance of water quality on polymer solution preparation and injection performance and reviews operational data acquired during the testing period. Polymer properties determined during the PIT will be used to optimise field and sector models and will facilitate the evaluation of polymer EOR in other giant, heterogeneous carbonate reservoirs, leading to improved recovery in ADNOC and Middle East reservoirs.

Simultaneous injection of miscible gas and polymer (SIMGAP) has been proposed as a technique for improving sweep efficiency of miscible CO2 in a giant heterogeneous carbonate reservoir (B) with harsh conditions of high temperature and salinity in Abu Dhabi. A pilot is planned to evaluate the concept. Reservoir simulation models were built to design the pilot and to evaluate field-scale deployment of SIMGAP, assuming the pilot is successful. This paper describes the pilot design and the workflow used to assess large-scale deployment. Reservoir-B comprises of two main units, Upper and Lower, which are in hydrodynamic equilibrium but have large (10-100) permeability contrast, due to which, water injected into the Lower unit rapidly crossflows into the Upper unit bypassing significant volumes of oil in the Lower unit. Hence, the Lower unit forms a key target for enhanced oil recovery (EOR). In the SIMGAP process, miscible gas (CO2) is injected into the Lower unit and polymer solution is simultaneously injected into the Upper unit. Provided the polymer solution generates sufficient resistance to flow in the Upper unit, crossflow of CO2 is suppressed, and the Lower unit is efficiently swept by miscible CO2. A SIMGAP pilot has been designed, consisting oftwo central 3000-ft horizontal injectors for polymer injection in Upper, and CO2 injection into Lower unit respectively and two 3000-ft horizontal producers in the Lower unit 250m from the central injectors on either side. Reservoir sweep will be determined by repeat logging of vertical observation wells and the polymer solution in the Upper unit will be sampled to confirm in situ viscosity. A reservoir model was built and calibrated to field behavior to design the Pilot.The relevant design parameters include offtake rate, polymer and CO2 injection rates, polymer pre-flush and polymer solution concentration and viscosity. A key prerequisite for proper modelling of SIMGAP is to have a static model that captures the geological heterogeneity (e.g., vertical permeability contrast, all prevailing rock types) and a dynamic model that incorporates the SCAL derived capillary pressure (both drainage and imbibition) and relative permeability curves. The model forecasts show that significant sweep of the lower zone is achieved with SIMGAP compared to both water or gas injection and that the process is stable and robust to lateral and vertical reservoir heterogeneities. The SIMGAP process has never been piloted and it involves a hybrid of two EOR techniques CO2 injection and polymer flooding in harsh conditions of both high temperature and salinity. In addition, field deployment of SIMGAP was directly simulated in the sector models. The resulting field profiles were used to evaluate SIMGAP deployment in Reservoir-B.