Pulsed Neutron Monitoring of the First CO2 EOR Pilot in the Middle East

Abstract

Using borehole measurements to monitor carbon dioxide (CO2) floods in the reservoir is essential to properly understand the behavior of the injected fluids and the flow patterns. Pulsed Neutron logs provide essential measurements for the evaluation of saturation in the injectors, producers and observers. However, the CO2 environment is as yet uncharacterized in the industry. Hence, reliable inferences require that either the measurement is immune to the borehole environment or that the perturbation is minimal and can be easily corrected. Where corrections are required, suitable benchmarks should be planned in advance to verify the accuracy of the corrections. These corrections should be based on the physics of the measurement to the maximum extent possible. On the first CO2 EOR pilot project in the Middle East—unique in the world because the CO2 flood was implemented with the reservoir at original oil saturation—several pulsed neutron surveys were recorded in the injector, observer, and producer wells. The surveys included capture and inelastic mode acquisition. Several novel techniques of data acquisition and interpretation were successfully tried. This paper presents the steps in planning and executing the jobs and the results of the surveys. Limitations of existing characterization and those imposed by the measurement environments in the subject wells are discussed and we show, through comparison with benchmarks, that correction for the unusual borehole environment is possible. The paper illustrates how the different modes of pulsed neutron data acquisition complement each other in the individual wells in assessing the borehole environment, providing adequate input data to enable a multiphase reservoir fluid analysis, and yielding independent fluid saturations for effective comparison. The results of the analysis are compared with an openhole evaluation to help create a coherent picture of the reservoir.

CO2 Miscible Flooding for Enhanced Oil Recovery

“…They concluded that the minimum miscibility pressure (MMP) was 4630 psia, The optimum injection rates for immiscible and miscible CO 2 injection scenarios were 17,000 and 30,000 Mscf/day, respectively and oil recovery factor reach 36.59% [1]. Al-Aryani and others [61] have reported on the first CO 2 -EOR pilot test in the Middle East where pulsed neutron logging was used to monitor the performance of a CO 2 flood in one of the largest oil fields in Abu Dhabi, United Arab Emirates. The results of this test will be viewed with great interest based on the fact that it will have a significant impact on the application of CO 2 -EOR in many oil-rich countries in the Middle East with the potential for very large additional oil recoveries.…”

Carbonated water injection: an efficient EOR approach. A review of fundamentals and prospects

“…Injecting CO 2 alone is found to cause early breakthrough of CO 2 along fracture direction (Figuera et al 2014), which necessitates corresponding modeling of injection/production adjustment strategies in advance (Luis et al 2016). It is suggested that flood breakthrough in multilayered, multi-well CO 2 flood system can be identified through pulse-neutron production logs combined with permeability from the magnetic resonance (Aryani et al 2011). Unlike miscible flooding, gas breakthrough is more predominant in immiscible flooding in which gas moves through high permeable channels as evidenced in Yaoyingtai oil field (Yuncong et al 2014).…”