Assessment of Sweep Efficiency and Breakthrough Using CO2, H2O, Carbon and Hydrogen Isotope Composition in a Water Alternating with Gas EOR Project in Onshore Abu Dhabi, UAE

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.

Application of stable carbon and hydrogen isotope technology in the determination of gas sources from limestone layers at Shuangliu mine, China

Stable carbon and hydrogen isotope technology is used in determining gas sources in coal mines. Coal measures at the Shuangliu mine mainly contain nine coal seams (i.e. No. 2 to No. 10) and five limestone layers (namely, L1 to L5). The coal seams are interbedded with the limestone layers. A large amount of methane is adsorbed in the limestone layer, and the actual measured maximum gas pressure is 1.3 MPa, posing a serious gas emission safety risk in roadway excavation in the coal measures. In order to effectively manage the safety risk of gas emissions, it is necessary to determine gas sources and take necessary control measures. In this study, 50 gas samples were taken from the coal seams and 10 gas samples were collected from the limestone layers. These samples were measured for their composition and stable carbon and hydrogen isotopes. Stable carbon and hydrogen isotope tracer separation technique and multi-source linear calculation methods were used to analyze the measurement results. The study shows that 84% of gas in the L1, L2 and L3 limestone layers comes from the No. 8 coal seam and 11% from the No. 9 coal seam; gas in the L4 limestone layer is mainly from the No. 8 (44%), No. 7 (37%) and No. 6 coal seams (16%), and gas in L5 limestone layer mainly comes from the No. 6 (59%), No. 7 (23%) and No. 8 coal seams (13%). The research results can guide the design of gas drainage boreholes before roadway tunneling, so it has important guiding significance in the formulation of comprehensive gas control schemes.