Seismic Imaging and Characterization of an Isolated Carbonate Buildup: Tengiz Field, Republic of Kazakhstan

High-fold and wide-azimuth 3D seismic data was recently acquired and processed over Tengiz Field, leading to improved reservoir characterization and field management. Tengiz is an isolated Paleozoic carbonate build-up containing 26 billion bbls of oil in place. Pre-stack depth migration (PSDM) has been performed to image the reservoir and correct for overlying “dirty salt”. Tengiz Field is one of the world’s deepest supergiant fields and has a complex depositional and diagenetic history.

A thick deposit of fractured microbial boundstone is recognized in the outermost platform and upper slope facies in the prograding Serpukhovian sequence. This unit tends to be highly fractured and, despite relatively low matrix porosity, wells have very high productivity (~10,000 bbls/d). Thick deposits of in-situ boundstone occur on the NE slope of the platform margin, whereas on the west side large-scale margin collapse has resulted in a narrower in-situ margin, and an expanded interval of displaced material in the middle slope. The new seismic data provide good definition of the spatial distribution and characteristics microbial boundstone facies.

High amplitude seismic events (referred to as “mega-amplitude” events) are observed in the 3D seismic. These mega-amplitude events may result from solution enhancement of fractures via deep-burial corrosive diagenesis, resulting in high permeability fairways. These seismic events correlate with evidence for cavernous porosity in wells including lost circulation, bit drops, open calipers, and cavernous zones on image logs. Identification of cavernous porosity is important for understanding field performance and targeting high-rate wells.

These mega- amplitude events have two orientation trends. One trend is parallel to the depositional strike of the platform margin, and the other dominant trend is normal to strike of the platform margin. These orientations coincide with fractures seen independently in image logs. These patterns may relate to deep-burial dissolution along fractures that formed during deposition and initial burial of the uplift. Stratigraphic control on the position of these events is also noted. Forward seismic models of these mega-amplitude events have been an important analysis tool for understanding the size and character of caverns imaged by the seismic.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California