3D OBN High Resolution Seismic Acquisition Design for Better Sub-Surface Imaging, Cheleken, Caspian Sea

Abstract

The Cheleken contract Area lies in the Turkmenistan sector of the South Caspian Sea, over an area of 920 Km2 and in water depth of 10 to 40 m. Located in a complex wrench faulted system orientated WNW-ESE from the Apsheron Peninsula in Azerbaijan to the Cheleken Peninsula in Turkmenistan, the cheleken fields have a large thickness of stack sand and shale reservoirs, with significant areal and vertical variation. The presence of strike slip faults, gas Chimney, H2S in some reservoir fluid, and low sweep efficiency due to the aforementioned geological complexities are challenges that need to be addressed. In 2004, the first seismic acquisition campaign was carried out by Dragon Oil in order to get a full dataset of seismic data covering the whole field, the acquisition technology considered for this dataset was Ocean Bottom Cable (OBC) and it was designed to cover the entire stratigraphic column down to deeper sections (approximately 7000 meters), therefore, deep objectives were not properly imaged due to technical limitations at that time. Seismic resolution was compromised and this OBC technology couldn't account for surface obstructions among other technical and logistic limitations. In 2015, Dragon Oil started with the idea to acquire a new seismic dataset with improved technology to aid in the better definition of sub-surface targets and define a more detailed and reliable structural framework as input for the Static and Dynamic Modeling Process. The ultimate goal of acquiring a new seismic dataset considering OBN Technology, was to define an optimal drilling strategy based on a more robust and reliable static and dynamic modeling of the field. Ocean Bottom Node Seismic has emerged as an effective technology for seismic exploration/development in numerous challenging acquisition environments with the key added value of higher data quality and much better seismic imaging. By placing receivers on the seafloor and decoupling the source from these receivers, the recorded data offers high quality imaging through improved multiple suppression and better subsurface illumination, without limitations existing with conventional streamer operations. Full Azimuth, long offset illumination, high fold are characteristics of Ocean Bottom Node (OBN) acquisition technology and it's proven successfully in extremely complex structural/stratigraphic environments and highly obstructed areas. This technology unfolds a wide range of geophysical options to generate a detailed geomodel of the field and also unlocks additional technical studies and seismic analysis.