Presented at SPE International Improved Oil Recovery Conference in Asia Pacific, Kuala Lumpur, Malaysia, December 2005.
An Assessment of Engineering, Economical and Environmental Drivers of Sour Gas Management by Injection
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.