Many of the largest fields yet to be developed around the world contain oil, water, and high concentrations of sour gas.The fact that they are still undeveloped reflects the significant political and economic hurdles they have yet to overcome.Successful production of such fields will require careful management of surface resources (land, water, and power), subsurface resources (hydrocarbons), and associated streams (produced water, non-salable products, and E&P wastes).Several fields in the Caspian Sea are awaiting full development because they are burdened by the high expected cost and severe legal and economic risks associated with high hydrogen sulphide (H2S) content. Advantek International was contracted to undertake a comparative analysis of the engineering requirements, environmental impact risks, and economics for disposal of several associated streams in a Caspian field with 20% acid gas (CO2 and H2S).
Several technologies are available to the Operator for handling the acid gas after separating from the hydrocarbons, including chemical conversion to "benign" elemental components, underground sequestration (disposal), and underground injection for enhanced oil recovery (EOR). Underground sequestration of some E&P associated streams (produced water, drill cuttings slurries, and completion fluids) have been practiced for many years, as has been injection of natural gas and CO2 for EOR. Sour gas injection, however, is a relatively new technology, with a limited experience base.
This paper reviews comparative economic and risk analyses of various acid gas management options available to developing sour fields, considering the impact on recovery (including rate, ultimate total volume, engineering capacity), human health and safety risks, impacts on the environment, reputation consequences, implementation complexity, initial investment (capital and lead time), and potential regulatory restrictions (based on current North American standards, recent judicial actions, and Kyoto Protocols). The greatest opportunity for both improved value and reduced risk lies with reinjecting the acid gas for EOR.While uncertainty regarding the range of value is large, there are no risks that should be considered too severe or unmanageable to undertake this option.
Several discoveries in the Caspian Sea deal with reservoirs that typically contain oil, water and high concentrations of sour gas. Countries surrounding the the Caspian Sea (Kazakhstan and others) are in transition toward a free market in energy and encouraging foreign investment, but at present there is far less demand for gas than the expected large volumes of associated gas to be produced from the Mega Fields in the area(Tengiz, Uzen, Karachaganak, and Kashagan, etc.).Except for Karachaganak, these fields are not connected to national gas marketing pipeline infrastructure, so demand for the natural gas component will be limited to field locations for local power or reinjected for reservoir pressure maintenance.
The composition of both the associated and solution gas from these Caspian fields contains up to 20% H2S and 5% CO2.Despite the small demand for gas processing, the excess H2S resulting from gas and liquids separation is expected to generate some 15,000–20,000 tonnes of sulphur per day in Kazhakstan alone.At Tengiz field, separated H2S is converted to solid sulphur and stored in surface accumulations that resulted in legal action and significant fines by the Kazhakstan government.Uzen's development is being held up, waiting on an export pipeline system to China, for processing there.The Kashagan field may produce thousands of tonnes of sulphur per day during field plateau.Development hinges on the approval of the Republic of Kazakhstan (RoK) government, whose production-sharing agreements require all production to be treated as resource, rather than waste, necessitating the development plan includes a comprehensive management strategy for all associated streams.