The super Giant Kashagan field is located in a shallow-water (ice-locked during the winter), environmentally sensitive area of the Kazakh sector of the North Caspian Sea. The Kashagan field was discovered in 2000 by a consortium of oil companies. The current North Caspian PSA companies are affiliates of: ENI, ExxonMobil, Shell and TOTAL, each with 18.52% share, Conoco-Phillips (9.26%), Inpex and KazMunaiGaz (8.33%, each). Agip KCO (an ENI company) operates the field.
The Kashagan field is a deep, over pressured (initial reservoir pressure: 783 bar), isolated, carbonate build-up with a high-permeability, karstified and fractured rim and relatively low- permeability, stratified, platform interior. The field contains a 43-degree API light oil, with 15% H2S and 5% CO2, and contains more than 100 Tcf of associated gas.
One of the biggest challenges of the Kashagan field development is the management of huge volumes of highly sour associated gas. The consortium had essentially two options to address this challenge:
A commercially unattractive, but technically not challenging, conventional choice of evacuating the sour gas to shore for treatment (H2S and CO2 removal) and sales; or
A technically very challenging, but potentially economically beneficial, alternative of injecting the raw sour gas back into the reservoir.
This injection alternative, with its high discharge pressures and sour service, would extend the current capabilities of existing gas compression technologies. Nonetheless, it had the potential to significantly enhance oil recovery, as the Kashagan oil and injected gas are first contact miscible at pressures well below the initial reservoir pressure.
Before proceeding with such a decision (after all, miscible gas injection is usually a secondary, or even a tertiary, recovery technique), the consortium had to undertake extensive evaluations to ascertain the likelihood of subsurface and surface risks.
The paper describes the integrated approaches and the different technologies brought to bear to evaluate the likelihood of potential risks (such as breaching of cap rock integrity, early gas breakthrough or asphaltene precipitation), and to implement mitigating solutions. It presents the reservoir and gas management strategies to mitigate the risks of cap rock failure and premature gas breakthrough. It also mentions some of the technologies advocated to, notably, detect potential fracture growth, monitor gas front movement and shut-off high gas-oil ratio producing zones, efficiently and cost-effectively.