Integrated Karst Characterization From Seismic to Geologic Modeling in Kashagan Field, Kazakhstan

Abstract

The presence of karsts play an important role in carbonate fields due to their potential impact on HC volume estimates, development planning, well placement, and drilling operations. However, characterizing karst features remains challenging due to complexities in terms of karst origin and proper identification, concept-to-data calibration, and methods necessary to incorporate into geologic models. Forward seismic modeling suggests that, geologically reasonable, porous karst features can be associated with high amplitude and low impedance seismic attributes. Through the modeling results coupled with well calibration, specific ranges of low impedance amplitude are classified in the EMPreSS seismic volume to capture the distribution of large karst voids in the reservoir. The amplitude classification process results in a seismic geobody volume. Kashagan core characterization exhibits dissolution related to exposure (meteoric karst) and the migration of burial fluids (burial karst). Based on the core study and integrated with well results, including available dynamic data, stratigraphic position, karst analogs and knowledge of karst processes, each geobody is interpreted as either meteoric karst or burial karst in origin. Geobodies that related to seismic noise, geophysical artifacts and/or lithostratigraphy, were filtered out through manual editing. The result is a distribution of seismically derived karst geobodies predominantly focused around the carbonate platform margin. This spatial distribution is consistent with karst associated with flank-margin cave systems developed during sea-level lowstands and burial karst that was generated as aggressive burial fluids ascended from the basin through an extensive fracture system present in the Kashagan margin and slope. Recent development drilling in the margin region of the Kashagan reservoir targeted a number of seismic karst geobodies. Post-drill well results indicate that the majority of the penetrated seismic geobodies are interpreted as karst features with expected enhanced deliverability. From a geologic modeling perspective, seismic karst geobodies can be imported as deterministic objects into the geologic model and then used, in combination with other geologic controls, to condition the distribution of karst that is below seismic resolution. Reservoir properties in karst geobodies can be differentiated based on the tier of the seismic anomaly and / or the genetic classification of karst.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016