Abstract

Numerous oil and gas reservoirs in Kuwait are suffering from H2S contaminations. The H2S concentrations in the affected reservoirs vary significantly from low ppm ranges up to 40%. The H2S concentration levels are related to the generation processes. The high H2S concentrations observed in the Lower Jurassic reservoirs can be related to the TSR process. The dominant H2S generation process in the Upper Jurassic and Lower Cretaceous reservoirs is the thermal cracking of the organic sulphur compounds (OSC) occurring in the Najmah and Sargjelu source rocks. The H2S contaminations observed in the Cretaceous reservoirs show indications of multiple H2S sources. The bulk of the H2S in these reservoirs is generated in situ by the BSR process. In some fields clear indications for H2S migrated from deeper horizons e.g. via faults are observed.

H2S contaminations are also observed at the top site facilities at various stages of the production process. The source for those contaminations is only partly in the subsurface. In several cases a distinct increase of the H2S contaminations of the fluids on its way from the reservoir well to the processesing facilities is observed.

New sampling and analytical technologies tailored to the H2S problematic have been developed, which support the selection of the appropriate mitigation or remediation strategy. The utilization of modern low cost DNA sequencing technologies for the analysis of the bacteria and archea species provide essential information for the design of appropriate chemical cocktails for the mitigation.

Reservoir modeling and forecast technologies have been developed to predict the development of the H2S concentrations in a reservoir. However, for a reliable forecast - irrespective which modeling system or tool is applied - the understanding of the H2S generation process is essential. Furthermore good quality and reliable H2S measurements are mandatory for the history match.

The mitigation and remediation of H2S is a major cost factor in the field development and operations. Field souring i.e. the increase of the H2S concentration during field life is the worst case scenario, which could cause major investments to assure field production. Not only the costs for the H2S treatment materials (e.g. biocides, nitrate) but also the investments in corrosion inhibitors, H2S resistant pipes, valves, filters, and the upgrade of the processing facilities have a large financial impact. Furthermore HSE related measures and required safety and monitoring systems are increasing substantially the operation costs.

In view of KOC's ambitions to increase the oil production by 20% by 2020 and the subsequently expected increase of H2S production, a contry-wide coordination of the treatment concepts for the H2S could improve the efficiency of the mitigation operations and could potentially reduce the investments and operation costs related to the sour gas issue.

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