Comprehensive 3 Dimensional Seismic Data Analysis to Comprehend Faults Distribution, Characteristics & their Significance in Controlling Hydrocarbon Accumulations in Brittle Carbonate Reservoirs: A Case Study in United Arab Emirates

Abstract

Structural architecture of fault zones, their distribution across the field and impact on migration pathways & reservoir permeability play an important part in field development. Inspiration for this study was limited understanding of role that faults play in brittle carbonate reservoirs. Extensive fault interpretation study was planned for quantification of orientations, segmentation, offset magnitudes and fault zones spacing to define their implications on fluid flow in terms of sealing capabilities within reservoirs. A systematic structural interpretation approach was established by exhausting the combination of regional tectonic history, 3D seismic interpretation techniques, advanced 3D visualization, BHIs, drilling data, production data, pressure data and MDT data. This resulted in better and more thorough definition of structures and hydrocarbon distribution in reservoirs. Structural history of the field was analyzed to tie fault related observations with known tectonic events affecting reservoirs. A simple structural restoration with available data indicated that structures & fault zones probably resulted from regional WNW-ESE compression during late Cretaceous period. 3D seismic interpretation techniques & 3D visualization were exploited to interpret faulted zones present in the field. Geometrical attributes were extracted from conditioned seismic data to enhance discontinuities & edges. Interpreted faults were later tied with wells crossing faulted zones using BHIs & drilling data. Thorough analysis reveals that major faults are actually assemblage of numerous segments. Furthermore, lateral and vertical displacement gradients are observed near tip lines of the fault planes. Relay-ramp behavior between fault segments are variable, mainly dependent on their orientation relative to prevailing maximum horizontal stress direction. Accordingly, positive (popups) and negative (sinkhole) structures can be found along the major faults. Two major faults having larger throws, as compared to other faults, divided the field into three parts, namely, northern, central & southern. Fault transmissibility varies as function of slip magnitude, diagenesis history leading to minerals filling, and their orientations relative to current maximum horizontal stress direction. Field dynamic data unveils that magnitude of slip is one of the most significant factors in explaining sealing capabilities of faults in reservoirs. Numerous wells have been drilled in central & southern parts of field with continuous production from wells in central part since 2005. Pressure records have shown no pressure change in southern part till date. Additionally, MDT results showed different FWLs and GOCs in both parts of field which also point to complete isolation. Northern part of field is yet to be appraised. Possibility of faults, with significant throw separating the northern from the central part of the field, acting as a seal may not be ruled out. An appraisal well with extensive acquisition program has been proposed to uncover hydrocarbon potential in northern part of field.