A new approach for weak time-lapse anomaly detection using seismic attributes: Geology and production data integrated monitoring of miscible EOR-CO₂ flood in carbonates

Since the emergence of time-lapse, TL, seismic technology as a viable element of reservoir management, monitoring production and enhanced oil recovery programs, in carbonates, has been very challenging. Coupled effects of complicated petro-physical and/or lithofacies heterogeneities “difficult to model or image,” low compressibility “high stiffness,” and thinness of carbonates have made seismic monitoring a high-risk component of EOR programs requiring both highly repeatable 4D-seismic acquisition and weak anomaly-sensitive processing and interpretation approaches. Most important is the need to maximize interdisciplinary synergy among all reservoir management team members. In this study, we present a new non-differencing approach called “Parallel Progressive Blanking” (PPB) for detecting time-lapse seismic attributes anomalies. This approach is more efficient than differencing TL attributes and/or data in cases where weak anomalies are concealed by non-repeatable noise. Four 4D-seismic datasets, interpreted seismic lineaments, seismic facies, sedimentological models and production data provided a means of testing and validating the PPB approach of interpreting weak TL-seismic attributes of anomalous zones observed during a miscible EOR-CO₂ flood. Using four TL-seismic datasets and applying the PPB approach, we have successfully monitored changes in seismic response related to the miscible EOR-CO₂ bank in the Hall-Gurney Field in Kansas. A predicted “via reservoir simulation” CO₂ breakthrough in April, 2004 in well 12 and an unpredicted delayed response from well 13 have been in compliance with the interpreted spatial outline of the injected CO₂ bank. Changes in pump strategies between two seismic surveys resulted in retreating of the CO₂ plume. Relatively fine (two months) survey-to-survey time spacing has assisted qualitative estimation of both reservoir heterogeneity and robustness of implementing the PPB approach, furthermore, dynamic flood management was aided by TL-findings.