Polygonal Faulting/Fracturing : Characterization (Seismic, Well Data) from a Carbonate Field, Abu Dhabi

Moen-Maurel, Laure¹, Frederic Jeanjean², Francois Gouth³, Sabah K. Aziz⁴ (1) Total, Pau, France (2) TOTAL, Abu Dhabi, United Arab Emirates (3) Total EP, Pau, France (4) ADMA, Abu Dhabi, United Arab Emirates

Recent refinement in 3D seismic processing and interpretation developed by Total has highlighted a new fracture pattern called polygons, pervasive over the whole sedimentary pile of the Abu Dhabi fields, both onshore and offshore. In order to address the issues of fracture characterization and their contribution to fluid flow specific processing were developed and combined from the stack steps to the attribute block definition. In tectonically precocious sedimentary basins and in gently dipping sedimentary wedges the outcome from this processing usually highlights the existence of right-angle joint patterns, comparable to what is classically known in outcrops from the bedding scale to remote sensing scale (satellite). In the case of the Abu Dhabi carbonate platform, over the whole of the seismic acquisition (from Permian Khuff upwards) the dominant pattern consists of 200m wide polygons (100-350m range) with no preferred strike, except near faults where polygons are reoriented into fault segments. Well data (imagery logs, cores, drilling, test and production data) show various characteristics for the polygon planes, specific to their strike and location: 1- minor throw (up to 5m), 2- cemented gouge leading to reduced horizontal permeability, 3- open and conductive fractures leading to preferred flow direction. Outcrop study of analogs is under evaluation to define the mechanical origin of the polygonal pattern. Preliminary results indicate that required external conditions are: 1- unbalance in fluid pressure between layers during compaction, 2- Equal horizontal stresses for Shx (min) and Shy, 3- Existence of a ductile mechanical formation below (salt) isolating (detaching) the platform carbonate from the “basement”. The present study shows how other scales of fractures (diffuse jointing to faults) interact with this little recognized pattern, both in outcrops and in subsurface.