Building a Robust 3-D Model for a Complexly-Faulted Reservoir: An Example from the Angostura Field, Offshore Trinidad

Liangmiao (Scott) Ye
BHPBilliton, Houston, TX

The newly discovered Angostura field in Offshore Trinidad presents an unconventional challenge for 3-D geological modeling.

The Angostura Sandstone reservoir comprises Oligocene-aged, gravity flow-dominated slope fan deposits. The complex tectonic history of Trinidad, having evolved from compressional to strike-slip regimes, has resulted in an unusually complex structural style. A number of normal, reverse, low-angle thrust, and strike-slip faults dissect the field into several major blocks and form complex geometrical relationships, such as “y”, “x”, “lambda”, and crossing faults, and the combination of these forms. With throw ranging from ten's to hundred's ft and a complex diagenetic history, these faults can potentially function as flow barriers or baffles or fluid migration paths.

Accurate presentation of these faults is critical to building a robust 3-D model to assist development planning. However, it is not a straightforward task. There is few well-established technique and approach for incorporating such complex faults through the entire modeling process. The challenges come from the difficulties in: 1) preserving the geometry of low angle faults without jeopardizing a sound simulation-grid geometry; 2) proper handling of the overshadow area and repeated sections associated with thrusts and reverse faults; 3) honoring these complex fault relationships at all the stages of modeling workflow; and 4) coherent migration of the model from one application to another, which is needed at least for conveying the geological model to flow simulator.

This talk will first describe the technical problems and then present an effective workflow that was developed and successfully tested through this study.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005