Tengiz field is a super-giant carbonate reservoir located in the Western Kazakhstan. The carbonate matrix consists of almost pure calcite, which makes it very attractive for acid stimulation. Over the years matrix acid stimulation has been successfully used in Tengiz to remove near wellbore damage and enhance well productivity. Despite successful production response from acid stimulation in the past, it was noticed from poststimulation surveillance analysis that tighter and less depleted intervals were often left untreated. This observation suggested that chemical diverting agents were not effective for long completion intervals and further opportunity for improvement was identified. In addition, existing two phase retarded acid had limitation due to high viscosity and had known issues during plant flowback. New acid stimulation design has been proposed and successfully executed in three newly drilled wells. This acid treatment utilized staged stimulation concept, where diversion was ensured by mechanical isolation of lower intervals with inflatable packer. New single phase retarded acid system was introduced to address operational and plant processing challenges with two phase retarded acid. Core flow tests were performed prior stimulation to evaluate effectiveness of different acid systems. Results of core flow tests and wireline log data were used during simulations on new generation of matrix acidizing modeling software to determine parameters for optimal wormhole creation. Proper planning and thorough technical assessment enabled execution of staged acid stimulation with new acid system incident free with less than 10% incremental cost in all three wells. Post-job surveillance program is in place to evaluate acid diversion and production contribution from tighter and less depleted intervals.

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The development of the giant Tengiz and Korolev oil fields might require a large and reliable industrial water source for future development. This paper shares best practices from a multidisciplinary team effort in characterizing the shallow aquifer water sources in the Tengiz area. The data set above the Tengiz oil zone is characterized by limited cores and large number of penetrations with logs, as well as 3D seismic. A subsurface study of the Tengiz area Post-Salt aquifers is challenging because of the old vintage of existing logs and limited core in shallower section of wells targeting Tengiz and Korolev oil reservoirs. A subsurface data gathering program was executed to acquire new logs, core from two new wells A-1 and B-1 from Alb-Cenomanian, Upper Neocomian, Aptian and Jurassic formations. All core and log data in conjunction with seismic improved our understanding of the depositional environments, connectivity and areal extend of numerous sand bodies. Core porosity and permeability very well match with new wireline logs. Based on information gained and new interpretation data, we now have better understanding of the geology of potential water source sands. Alb-Cenomanian and Upper Neocomian deposits were found to be the two largest aquifers in the Tengiz area. The Alb-Cenomanian has high net-to-gross with extensive fluvial channel belt sandstones. Reservoir properties are very good and water volume is very large. The Upper Neocomian consists of ribbon-like fluvial channel belts (2-15m thick) embedded within floodplain deposits and interbedded thin (i.e., <2m) crevasse splay deposits. Reservoir sandstone is moderate to excellent quality. The Upper Neocomian has stratigraphic barriers above and below – internally it exhibits some baffles and barriers associated with floodplain shales. Aptian and Jurassic sections were evaluated to be unattractive as water sources. Because of sand quality and higher water volume, Alb-Cenomanian and Upper Neocomian formations were selected as the best candidates for water source. New seismic interpretation, log and core data were incorporated to construct static models. Dynamic models for shallow aquifers are being built; the models will be used to support the industrial water source development plan for Tengiz and Korolev oil fields.