Williams-Stroud, Sherilyn C.¹, Freddy Yip², Haiqing Wu³ 
(1) ChevronTexaco, Bellaire, TX (2) ChevronTexaco, New Orleans, LA (3) ChevronTexaco, Salmiya, Kuwait

ABSTRACT: Investigating the Range of Interpretation Uncertainty in Poorly-Imaged Seismic with Structural and Geomechanical Modeling

The difficulties associated with interpreting small-offset faults in seismic data are magnified in reservoirs which are imaged below salt. In a sub-salt reservoir in a complex structural setting bounded on three sides by diapiric salt, a methodology was tested to validate interpretable faults and to predict the existence of sub-seismic faults and fractures. Possible interpretations of fault and horizon relationships were validated with 2-D and 3-D kinematic structural restorations, and different deformation scenarios were tested. In order to model sub-seismic fault development, stress conditions and rock response were then modeled for each valid restoration using an elastic boundary element model (BEM). The applied stress orientations and boundary conditions for the BEM were chosen to be consistent with each of the valid restoration scenarios. Mechanical properties of the reservoir rocks were constrained by well log data, and core data and fracture interpretations were used to constrain the evolution of the strain tensor with respect to development of the reservoir structure. The modeling results show for the specific structure in question a significant range for what is geologically probable, as opposed to the less restrictive range of what is merely geologically possible. Knowledge of probable sub-seismic discontinuities is used to reduce risk associated with drilling and provide data to support well planning in potentially compartmentalized reservoirs. The results identify where the biggest uncertainties lie, and serve to illustrate value added when validation via structural restoration is done near the beginning of the model building process, when unnecessary model iterations can be eliminated.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.