Leveraging 4D Seismic and Production Data to Advance the Geological Model of the Enfield Oil Field, Western Australia

The Enfield Oil Field has been producing since 2006. The field was initially developed with 13 horizontal and deviated wells in a subsea development, with both updip and downdip water injection. Exceptional seismic resolution and time-lapse acquisition allowed valid conclusions to be drawn regarding changes in pressure and saturation across the field. An initial 4D Seismic monitor survey was acquired seven months after first oil, with a further two monitor surveys undertaken at two-year intervals. The dynamic information this provided, combined with production history, identified a number of infill and sidetrack opportunities. After three phases of infill drilling and five years of production, it became increasingly difficult to validate the existing static geological model against the latest well results and the dynamic behaviour of the field.

A thorough review of the conceptual geological model was undertaken which included revising the depositional environment and stratigraphic correlation. The primary focus of the review was to integrate learnings from 4D Seismic and individual well production histories. Some injector-producer well-pairs were performing as expected while others appeared to be affected by barriers and baffles that were beyond 3D seismic resolution. The dynamic information was used to ensure that the stratigraphic correlation was both geologically valid and matched to actual field behaviour. Well results and detailed core characterisation led to a change in interpreted depositional environment, with one zone originally identified as shoreface deposits re-defined as the product of a deep-marine depositional system. Pressure and saturation signals from 4D seismic, as well as pressure data and fluid type information from infill wells permitted an improved understanding of fault seal and compartmentalisation. Better-than-expected recovery in some parts of the field led to an inferred field-wide flooding surface being re-interpreted as a series of shingled, non-continuous shales, acting as baffles rather than a barrier to vertical flow. Fundamental changes in depositional and architectural concepts arising from the integration of static and dynamic datasets necessitated a comprehensive re-build of the static reservoir model. The new static model was used to match field production history more accurately, thereby providing greater confidence about the distribution of remaining reserves and potential infill drilling targets.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California