Mechanical Earth Modeling of the Tengiz Field

A 3-D mechanical earth model (MEM) was developed for Tengiz to predict the long-term response of a reservoir to field development. The study aims at understanding the impact of reservoir pressure depletion on reservoir compaction and surface subsidence.

Tengiz Field, a deep, super-giant oil field located in western Kazakhstan near the north-eastern coast of the Caspian Sea, consists of Devonian through Carboniferous isolated platform carbonates with an areal extent of approximately 440 sq. km. The top of the reservoir occurs at -3850 m TVDSS and the oil column is at least 1600 meters. Although the producing formation is deep and the reservoir rocks are competent, reservoir compaction and surface subsidence are nonetheless observed at Tengiz.

The MEM for Tengiz and surroundings is constructed using the existing geology maps and is populated with the properties derived from well data and a history-matched reservoir simulation. Starting at the virgin reservoir pressure state, a series of depletion steps is run to simulate reservoir compaction and surface subsidence. The MEM predictions are calibrated against observed patterns of surface subsidence and subsurface stress orientations. Initial results show a good match between the modeled and observed surface displacement (Global Positioning System and leveling surveys, and Interferometric Satellite Aperture Radar). Further calibration of the model was undertaken to obtain a better spatial correlation with InSAR results. Testing of different scenarios indicates that salt thickness and post-salt faults both play a role in propagating the subsurface compaction from the reservoir level to the surface. The degree to which reservoir heterogeneity impacts compaction was also analyzed.

An important result of the study is the recommendation that the 3D MEM is updated regularly to incorporate ongoing reservoir surveillance and surface subsidence data to ensure that the impact of field development on reservoir compaction and subsurface stress remains within predicted range throughout the field production life.

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