Predicting Sub-Surface Fracture Systems by Modelling the Associated Deformation in Move: Examples From La Concepción Oilfield in Venezuela

Abstract

Spatial and temporal information on the distribution, orientation and intensity of sub-surface fracture systems can be obtained by modelling the geological history of a region to quantify strain and stress through time. Information on the distribution, orientation and intensity of sub-surface fracture systems is essential for modelling the evolution of many reservoir properties (e.g. porosity and permeability), but these data are generally not provided by fracture prediction techniques commonly used in the oil and gas industry. Mathematical extrapolation of fracture measurements from wells across an entire reservoir often fails to capture the complexity and lateral variation of natural systems; equally, seismic attribute proxies (e.g. coherency), also commonly used, only provide a snapshot of the present-day without providing any indication of how fracture systems could have evolved. Midland Valley's Move software provides a suite of tools to model geological processes, and quantify strain to make predictions about fracture systems. It has recently been improved with the implementation of elastic dislocation theory via the Fault Response Modelling module. The new module calculates displacements, strain and stress induced by slip on faults. Fault-related stresses can then be added to a regional stress field, or used in isolation, to calculate Coulomb stress changes on predicted or observed fractures in the surrounding rock. The tool also makes it possible to calculate Coulomb stress changes associated with any restoration or modelling operation that has been carried out in Move. This provides greater flexibility and allows different deformational mechanisms and geological processes to be considered and quantified in the context of fracture development. In the new tool, all possible fractures and slip directions can be examined to maximize the Coulomb stress change and determine fracture orientation optimal for failure. We have used the tools in Move to disentangle fracture development in a reservoir in La Concepción oilfield in the Maracaibo basin of Venezuela. Different events in the geological evolution of the region are modelled, with calculated strains and stresses used to predict fracture orientations and intensities. Predicted fractures are then validated by comparing them to observed data from wells and used to differentiate between two faulting scenarios (dip-slip or oblique slip). Petrobras Energia Venezuela are acknowledged for providing data.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015