Print this pageKarsting Processes in The Upper Paleozoic Carbonates of Southern Kazakhstan: Controls And Reservoir Implications
LAPOINTE, PHILIPPE A. and MARIE-CLAIRE BERNET-ROLLANDE
Frasnian through Early Bashkirian carbonates of the Bolchoi Karatau range from deep water to supra tidal facies that have been affected by multiple karsting processes controlled by tectonic and sedimentology. Surface water percolated via fault zones, fractures and joints. With depth, these more vertical systems linked with stratigraphically controlled networks, resulting in preferential leaching of interbeds. Fractures in mud mounds were opened and flank beds (off-mound and inter-mounds facies) exhibit partings that have been enlarged. Cavities are related to fenestrae, evaporite nodule enlargement and evaporitic collapse breccia.
Five main karst events are recognised, one is related to a late Carboniferous compression phase. Each event is characterised by a specific filling. Commonly all karstic systems are superimposed at the same locality indicating reworking of weakened zones.
Specific reservoir implications are: (1) production of significant horizontal and vertical permeability together with porosity in thinly laminated beds; (2) double porosity system in massive mud mounds: one is a karst related network with good permeability, corresponding to large channels, partings and fissures enlarged by water circulation, and the second is related to the host rock; (3) extended drainage systems with anastomosing vertical connections in faulted and fractured zones. That systems may side-step across major facies changes; (4) presence of karstic collapse breccia with fracture type porosity.