Title : Well design optimization in high H2S conditions
Abstract:
The production of sour gas, characterized by high concentrations of hydrogen sulfide (H?S), presents significant challenges to well integrity and corrosion management. This paper is about cost optimization based on the latest in-house experience and actual field verification. As a result, significant CAPEX and OPEX savings on well design and maintenance have been achieved with no impact on HSE and Integrity.
High sour gas reservoir has been operated through gas producing wells equipped with high grade corrosion resistance alloy material in their lower part. Upper completion above the packer was carbon steel with the provision for the continuous downhole inhibition through the chemical injection valve installed in the side pocket mandrel above the packer. Those valves require regular replacement and re-dressing. In case valve malfunction, the well is scheduled for periodic batch treatment with high concentration of the inhibitor. Based on the international practices and actual observations for the last years, this well design was challenged.
It was assumed based on the gas composition and production parameters that most of the wells of this reservoir can be operated without continuous inhibition. Several well candidates have been selected for the verification. There was a baseline corrosion log (mechanical multifinger caliper) recorded in those wells, and continuous downhole inhibition was deactivated afterwards. The same time-lapsed corrosion log was periodically repeated later during this period in those wells and results confirmed that there is no requirement for the continuous inhibition of the gas producers for this reservoir operating in the same envelope range.
Business impact and potential added value from cancellation of CIV preventive maintenance:
- Elimination of one day slick line operation per well.
- Saving on CIV (chemical injection valve) redressing cost.
- Elimination of one day of deferred well production due to CIV maintenance operations.
- Eliminating extra operational risk of wireline interventions for CIV retrieving / installation.
- Eliminating extra leak path in primary well barrier (SAP A issue) due to CIV failure.
- Elimination of batch treatment operations.
- Well Integrity KPI improvement after risk level reassessment.
Overall added value:
- saved OPEX due to absence of the well intervention and maintenance requirements for the chemical injection valves of these wells.
- saved OPEX due to absence of the batch treatment requirements in case of valve failure.
- released field operational resources for other activities.
- Saved CAPEX for all future new wells and workovers for the producers of this reservoir due to applying full carbon still completion instead of CRA.
Audience Take Away Notes:
- Evidence of the industry-conservative approach in terms of material limitations for H2S environment
- Opportunities for significant budget savings in high H2S fields
- Improved HSE status
