The key objective of the CO2 WAG Pilots is to confirm improved sweep and to enhance oil recovery under CO2 WAG relative to water flooding. Two CO2 WAG Pilots are in progress in a giant Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with two vertical pilot observers. A detailed monitoring plan was designed and implemented to monitor pilots’ performance and track CO2 breakthrough and flow path. Injectivity of both water and CO2 was determined in the WAG cycles to investigate any loss of injectivity. The producers are being tested daily for oil rate, water cut, GOR using multi-phase flow parameters (MPFM) while portable test separators are used every quarter to validate these measurements. PVT analysis of produced fluids are being carried out on samples from portable test separators and MPFM sampling point to monitor CO2 content. Different gas and water tracers have been injected to trace the movement and breakthrough of injected fluids into the pilot producers. Carbon and oxygen-isotope analysis for produced and injected CO2 gas is also carried out to monitor CO2 breakthrough. RST logs in the observers demonstrate good sweep across different layers of the reservoir and show that WAG is providing mobility control to CO2. Several data sources were analyzed to determine CO2 breakthrough time and the CO2 flow path. Analysis of CO2 in produced gas has determined the timing of CO2 breakthrough. This is supported by the isotopic analysis of injected and produced CO2 in pilot producers and near-by producers. The tracer analysis results unambiguously identify the source of the produced CO2. Injectivity analysis of both CO2 and water showed injectivity of CO2 was either the same or higher than water injectivity. Moreover, no loss of injectivity was observed between WAG cycles. The pilot has been operated successfully without HSE issues since 2016. Corrosion logs are acquired within the extensive monitoring program along with inhibitor injection to avoid any Asphalting deposition. The paper discusses the performance of the first multi-well CO2-WAG pilots in a giant onshore reservoir in Abu Dhabi which is used to de-risk multiple CO2 WAG full field projects in ADNOC reservoirs. It also highlights the importance of the different reservoir monitoring tools for improved understanding of the pilots which will be used as a basis for implementing CO2 WAG for the full area development.

Two CO2 WAG Pilots are in progress in an Abu Dhabi Oil Reservoir. Each pilot has one horizontal producer and two horizontal injectors along with 2 vertical pilot observers to monitor the movement of flood front away from the injectors. The pilots are being monitored based on a detailed reservoir-monitoring plan. The paper discusses in detail various activities and the results related to the pilot monitoring. Methods, Procedures, Process The wells are being tested for oil rate, water cut, GOR on a daily basis using MPFM. For calibration purposes portable test separators are used every quarter to validate the rate, water cut and GOR measurements. Separator PVT samples from pilot wells are collected every quarter for PVT analysis. In addition PVT samples are also collected from the pilot wells and nearby wells every month from the sampling point near MPFM to monitor the CO2 content in the produced gas. Online CO2 analyzer is fitted on the surface flow line connecting pilot wells to the RDS to provide continuous measurement of CO2 in the produced fluid. Produced water is also sampled for detailed compositional analysis. Different gas and water tracers have been injected through the pilot injectors to trace the movement and breakthrough of injected fluids into the pilot producers. Sampling and analysis for tracer is carried out on a regular basis. Carbon and oxygen Isotope analysis for produced and injected CO2 gas is also carried out in order to monitor the breakthrough of injected CO2 into the pilot producers. There is a good difference in the carbon and oxygen isotopes of injected CO2 and the CO2 present in the reservoir. To monitor the changes in water and gas saturation with time across different layers a set of Pulsed neutron (RAS) logs are run in the observers on regular basis. PLT logs are run in the injectors and producers to check the distribution and conformance of the produced and injected fluids along the horizontal wellbore. Walk away VSP surveys are being carried out on regular intervals for one pilot to monitor the injected fluids distribution in the pilot area. The paper describes all these reservoir monitoring activities in detail. Results, Observations, Conclusions Analysis of Carbon oxygen RST logs are helpful for tracking fluid saturation changes and CO2 movement across the logged intervals. The RST logs in the observers demonstrate good sweep across different layers of the reservoir. Analysis of CO2 in produced gas has resulted into correctly pointing out the timing of CO2 breakthrough in the producers. It is well supported by the CO2 isotopes analysis for the injected and produced CO2 through pilot producer and nearly producers. The tracer analysis results show clearly the injector from where the injected CO2 has reached the producers. The PLT logs demonstrate good conformance for CO2 and water injection across the horizontal section in the injectors. All these monitoring activities provide a good source of data for further analysis and improved understanding of the pilots. Novel/Additive Information The paper discusses the usefulness of different reservoir monitoring tools for improved understanding of the pilots, which will be used as a basis for implementing CO2 WAG for the full area development.

In alignment with most company's vision to reduce greenhouse effects by expanding CO2 carbon capture and utilization for oil fields, CO2 gas is injected into the reservoir to enhance oil displacement and maintain reservoir pressure. Since CO2 gas is miscible in the oil, the gas flood front is not piston-like; the gas is slowly absorbed by the oil changing the oil properties. Detection of the CO2 plume is necessary to monitor CO2/ injected water/ oil distribution (at and away from the well) and to track the effectiveness of the complicated CO2 WAG injection process in terms of improved sweep efficiency. Monitoring CO2 flood front movement requires a logging measurement that can distinguish oil from CO2 in the formation. This measurement must have a sufficiently large dynamic range for the change from no CO2 to a high CO2 saturation to be distinguished within measurement error. This paper highlights the utilization and integration of Reservoir Analysis System (RAS) and Noise tools in CO2 plume detection. It also highlights some of the limitations of the RAS tool in high water transition zone in CO2 WAG environment. As the oil is push away from the injection well, the flood front will be characterized by oil having varying amounts of miscible CO2 gas dissolved in it. The rate and composition of the injection gas determines how much of the oil that will expand. The density of the oil may not change much (since the oil density is close to the CO2 gas density) but the hydrogen density of the oil will decrease considerably as is the case for CO2. Another factor that controls the CO2 plume movement is the stratigraphy of the heterogeneous carbonate reservoir – where the coarsening upwards trend of the facies associations of High Stand Systems Tract (HST) coupled with pervasive cementation, creates non-uniform movement of CO2 plume vertically and spatially. Logging results shows Neutron porosity (PHIRN) and PNC near/far capture ratio are the preferred log measurement curves because they have the most sensitivity to the large decrease in hydrogen index when CO2 replaces oil or is dissolve in oil. Other curves like Ratio of Near to Long at Burst (RLNB), Long Inelastic Rate Sigma (LIRS), temperature and noise logs also play significant roles in CO2 plume indications. The outcome of this study has helped understand the vertical and lateral extent of the CO2 WAG flood front, estimate saturations, evaluate the well integrity, and locate un-swept zones. Additionally, RAS data is hard data used as calibration (blind test) to check the robustness of the dynamic model.

Measuring sweep efficiency and understanding breakthrough are the most important parameters to assess an Enhanced Oil Recovery (EOR) project having Water Alternating with miscible CO2 Gas (WAG) injection. The objective of this study was to use CO2, H2O and isotope compositions to assess sweep efficiency and breakthrough in producer wells in an ADNOC Onshore field in order to take the necessary actions for project optimization (e.g., injector and/or future producer well location optimization). CO2 and H2O compositions, along with their respective carbon and hydrogen isotopes, was integrated with downhole pressure gauge data to evaluate the impact of WAG operation on EOR. It was understood at the start of the project that an isotopically distinct injected CO2, compared to the oil associated CO2, would assist in the evaluation of sweep efficiency and breakthrough. The injected CO2 used in the WAG comes from a steel mill that is isotopically very distinct (i.e., significantly light) from the oil associated CO2. CO2 and H2O are injected periodically in the reservoir through designated injectors distributed over the field. The initially produced oil associated CO2, H2O, carbon and hydrogen isotope values were available as reference to measure the extent of sweep efficiency and breakthrough. Injected H2O and CO2 compositions and their respective hydrogen and carbon isotope values are measured at each injection cycle (so called campaigns). This is then followed by periodic compositional and isotopic measurements of the same components in oil and water producer wells to measure the extent of breakthrough. CO2, H2O composition and carbon and hydrogen isotope measurements in injector and producer wells indicate that the injected CO2 is preferentially breaking through in certain parts of the field. This indicates heterogeneous reservoir quality distribution throughout the field with better reservoir quality (e.g. higher permeability) between injector and producer wells having faster breakthrough. The compositional and isotopic measurements are sensitive enough to register compositional changes in the producer wells relatively faster than assessed by downhole pressure gauges.