NUMERICAL EXPERIMENTS OF FRACTURE PATTERNS AND FAULTING ADJACENT SALT FLANKS IN CONTRACTIONAL AND EXTENSIONAL SETTINGS

Sediments adjacent salt flanks are often structural traps, and therefore, prime targets for hydrocarbon exploration. Conceptual models predict a potential of high fracture intensity in these sediments which could enhance permeability. This necessitates the interest in predicting and quantifying fracture location, orientation and density. However, these efforts are often limited by a combination of poor seismic resolutions owing to salt overhangs or steeply dipping beds around the flanks of diapirs. Though well logs and drill cores may provide insights in estimating fracture intensity at these sites, they possibly suffer from biased and limited sampling which depends on the position of the well in addition to likely reorientation and disaggregation during core recovery and preservation. Understanding the fracture patterns and faulting will help improve hydrocarbon recovery and assessment of seal integrity.

This study utilizes a two-dimensional visco-elasto-plastic finite element analysis and fracture potential methods to predict fracture occurrences and locations around salt flanks under different tectonic settings. The study also evaluates the sensitivity of elastic properties, internal friction and dilation angles of sedimentary sequences and the resulting fracture distributions and/or faulting.

Modeling results indicate the likelihood of shear fractures occurrence close to the flanks and extensional faults dipping away at the flanks under contractional and extensional settings respectively, with friction and dilation angles having a control on the faults’ inclinations. These deformation patterns have been observed in extensional settings in the North Sea, the Gulf of Mexico and contractional settings in Angola. Also, pervasive scatter in fracture orientations is observed in strata along the diapiric margin which are likely to reactivate as diapir growth continues. This could breach the integrity of steeply upturned or growth strata acting as seals and/or permeability enhancement or damage.