Applied Sequence Stratigraphy Combined with Geological Modeling of the Greater Cheleken Area (Central Caspian Basin, Turkmenistan) Using New 3D OBN Acquisition to Reveal Channel Complex Systems from Delta to Deepwater Environments in Plio-Pleistocene Clastic Reservoirs

Abstract

Abstract The Greater Cheleken Area (GCA) reservoirs, developed offshore by Dragon Oil, are located along a complex NW-SE dextral transcurrent zone that separates the Northern and Southern Caspian Basins (SCB). This area hosts numerous hydrocarbon fields within thick, highly faulted Pliocene-Pleistocene clastic successions of the paleo-Amu-Darya Delta System, originating in the N-Balkan Fold Belt. We present a new model for the geological evolution of this region, based on the analysis and sequence stratigraphy interpretation of new 3D OBN seismic data, well logs, and integration with existing published data. With the new 3D OBN acquisition, Dragon Oil has both PSTM and PSDM data for analysis, employing a sequence stratigraphy approach. Horizon markers have been defined using sequence boundaries and flooding surface markers for detailed interpretation. The seismic data reveals promising geological features from the Apsheron to the red bed series reservoir levels. Seismic sequence stratigraphy has identified various stratigraphic components, such as basin floor fans, channel levees, and prograding deltas. Fault interpretation has revealed faults extending from the Miocene level to younger levels of the Apsheron, exhibiting typical positive flower structure configurations. Unconformity-bound sequences of alternating sandstones and shales, with limited limestones, conglomerates, and evaporites, are deposited in environments ranging from shallow marine, delta front, and delta plain to alluvial, lacustrine, and deepwater. These sequences include the Uppermost Miocene to Lower Pliocene Red Series (Lower, Middle, Upper Red Series), Upper Pliocene Akchagyl Formation, Lower Pleistocene Apsheron Formation, and Upper Pleistocene to Holocene, comprising twelve productive levels. Hundreds to thousands of mappable faults are connected to deep-seated shear zones and exhibit fault-sealing characteristics that create highly compartmentalized reservoirs with vertical and horizontal separations. These faults vary in shape and size and display continuous Pliocene-Pleistocene syn-sedimentary activity, including sediment thickness heterogeneities, pinch-outs, lateral facies changes, channel structures, and inversion structures. The sedimentary complexity as well as structural geology configuration described through the new 3D OBN data provides fundamental insights into the major challenges in reservoir production strategies and opens new opportunities for exploration and appraisal.