Use of Outcrop Analogues for Characterization of from Upper Paleozoic Carbonate Foreslope Reservoir, Karachaganak Field, Pricaspian Basin, Kazakhstan
Foreslopes of reef-rimmed carbonate platforms are composed of a spectrum of deposit types that exhibit complex vertical and lateral facies relationships due to partitioned contributions from multiple sediment factories via a variety of resedimentation processes. This depositional heterogeneity is often below the resolution of seismic imaging and poorly constrained through well log and core correlation. Outcrop exposures provide continuous and high-resolution facies, stratal, geometrical, and juxtaposition information that is generally not available from subsurface data, but critical for characterizing carbonate foreslope systems.
Karachaganak Field, northern Pricaspian Basin, Kazakhstan, is a reef-rimmed, Permo-Carboniferous isolated carbonate platform with an oil column that resides primarily within steep, progradational foreslope strata. Seismic mapping of the foreslopes at Karachaganak identifies a range of clinoform characteristics (i.e. continuity, curvature, declivity), margin configurations (i.e. accretionary, escarpment), and stratal terminations (i.e. onlap wedges, internal downlap). A narrow corridor of high-quality seismic data and poor core coverage to date warrants the use of outcrops to further develop play concepts and characterize reservoir attributes.
Extensively-studied outcrop exposures of carbonate foreslopes, including the Upper Devonian (Frasnian and Famennian) of Western Australia, the Lower and Upper Permian (Wolfcampian, Leonardian, and Guadalupian) of west Texas, and the Upper Triassic (Carnian) of northern Italy, together display similar ranges of clinoform, margin, and internal geometries to those observed at Karachaganak. Application of the outcrop information provides a linkage between seismically-determined stratal patterns and sediment type, as well as helps to constrain the timing and distribution of significant processes such as margin collapse, megabreccia emplacement, and bypass of grain-dominated accumulations into the basin. Integration of available subsurface data and insights from outcrop analogues ultimately enables enhanced prediction of reservoir quality, connectivity, and architecture in steep carbonate foreslopes, as well as other heterogeneous carbonate settings.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009