Reservoir Characterization of Fault-Related Dolomite Bodies from Outcrop Analogs: Application to Carbonate Reservoirs

Stefan Schröder¹*, Sylvain Rigaud², Sabrina Zerti¹, Jean Borgomano², Bruno Caline¹, Jean-Paul Gomez¹, Jerôme Hennuy¹, Eneko Iriarte Avilés³, Juliette Lamarche², Mikel Lopez-Horgue⁴, and Marina Sudrie^1
1Total, France
²University of Provence, France
³University of Cantabria, Spain
⁴University of the Basque Country, Spain
*[email protected]

Many subsurface carbonate reservoirs contain evidence for dolomitization associated with tectonic fluid circulation that has significant impact on reservoir properties. However, reservoir geometry and internal reservoir characteristics (diagenetic phases, porosity types, heterogeneity of pore networks) remain often poorly understood. Outcrop analog studies of Jurassic-Cretaceous carbonate platforms in France and Spain have potential application to dolomite reservoirs in the Upper Khuff Formation (Permian-Triassic) and the Garian Formation (Cretaceous, Libya). Depositional textures in the outcrop examples range from mudstone to oolitic grainstone. The transtensional tectonic setting was conducive to dolomitization by ascending Mg-rich fluids. Geometry and reservoir characteristics were studied using traditional and Lidar outcrop mapping, petrography, petrophysics, and 3-D-scanner pore network imaging. Fault conduits exerted a dominant control on dolomitization near fault corridors. Length and width of the resulting dolomite bodies vary from m-scale to 100s of m. Despite heterogeneous internal reservoir distribution, good reservoir properties are correlated with advanced dolomitization stages, whereas host rock texture has little influence. Pore networks are vuggy and inter-crystalline. With increasing horizontal distance from faults, stratigraphy and local discontinuities (bedding planes, porous facies, burrows, fracture networks) controlled fluid movement. Planar and lenticular bodies of porous dolomites commonly are developed in permeable horizons. Bodies usually are dm- to m-thick, and they extend laterally between 10s of meters to several km. Despite the good reservoir properties often associated with fault-related dolomites, and the presence of suitable seal rocks, the fault corridors have an associated risk of hydrocarbon escape. Increased reservoir connectivity may result in high recovery and water production.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain