WHAT ARE GEOTHERMAL WELLS?
Geothermal energy plays a leading role in the world’s energy sector and the reduction of carbon dioxide footprint. Petroleum and geothermal well drilling have different geological and physical features including rock types, reservoir pressure, temperature, well and casing design and the well completion programme.
Despite the great benefits, various issues exist currently impeding a wider uptake of geothermal wells including the aggressive nature of geothermal fluids, high temperatures, and the high costs of investment. Over numerous decades, the cost of developing a geothermal field was estimated at 4.5M-5.5M USD per installed megawatt (MW,) of which 50% is spent on drilling and completion. It is therefore important to constantly monitor the health of the well barriers through the well’s lifecycle to ensure well integrity and protect the investment [1].
INTEGRITY ISSUES
Thermal-well operations come with a range of Well Integrity threats. Typical examples include [2].
- Lost circulation and wellbore collapse are frequently encountered in geothermal well drilling. These problems can lead to poor cement jobs.
- Poor cementation leads to casing expansion and high temperatures result in cement strength retrogression.
- The presence of H2S can cause corrosion and subsequent leakage in the casing.
- Other integrity issues are burst, collapse, buckling and decoupling of the casings, mechanical wear and tear, wellhead thermal expansion, and scaling.
HOW CAN WE HELP
Asset Integrity Engineering provides a wide-ranging set of consultancy services and dedicated software solutions across the entire lifecycle of thermal well operations.
We have recently conducted a study on a major geothermal well operation utilising our WIMS software Veracity Wells. The objective of the project was to conduct a risk assessment of a complex high temperature and pressure (HPHT) geothermal well.
The dual barrier system well was commissioned in 2016 and normal operation consists of partially equilibrated, low pH and sulphur concentration water being produced through a production liner instead of a tubing or completion string. The well is not equipped with a Xmas tree.
For the study,
- All relevant documents related to drilling, casing and cementation reports, well offset data, ultrasonic thickness gauging results, assessment of low pH wells, post-completion test reports, and the well schematic were critically reviewed.
- Well design details along with its schematic and geographical location were uploaded to Veracity Wells. After identifying all well barrier elements, they were categorised as primary and secondary barriers and selected from the prepopulated list on Veracity for further integrity assessment.
- A NORSOKD10-compliant integrity assessment was conducted to appraise and justify the final status of primary and secondary well barriers and provide additional mitigation requirements.
- Corrosion compliance and in-service corrosion management data was analysed and dynamically linked to the well control barriers in the software.
- The final integrity status of the well was assigned.
BENEFITS
Well Barriers Integrity Study
AIE’s study revealed significant opportunities to improve integrity and reliability of the well in question. Our recommendations included:
- Providing a more robust integrity demonstration of the caprock formation sealing ability.
- Regular annuli pressure monitoring above the cement to prevent pressure cycling and hence reducing fatigue.
- Providing improvement recommendations and optimisation of the periodic inspection, function, and leak testing of the wellhead valves.
- Providing targeted recommendations to improve water chemistry, flow rates, operating conditions and sand management to improve operational corrosion control.
- Adoption of our VercaityApp to support all field data collection through one integrated platfrom.
AIE provides clients with a complete well integrity management service offering for both onshore and offshore assets. We employ leading industry experts and support all aspects of the Well lifecycle from downhole material selection through to a complete Well decommissioning consultancy service offering.
OUR WELL INTEGRITY SERVICES INCLUDE:
- Well Integrity Management Systems (WIMS)
- Strategies & Procedures
- Barrier Assessment
- Well Monitoring & Surveillance
- Annual Integrity Assessment
- Materials Selection
- Corrosion, Chemical & Flow assurance Management
- Life Extension Surveys
- Annular Pressure Management
- Decommissioning / P&A
- Compliance Audit& Reviews
- Data Collection, Analysis & Integrity Reporting
- Failure Assessment
- Engineering Consultancy & Troubleshooting
- Technical work instructions & Performance Standards
- Environmental Impact assessment
- Well Integrity Training
REFERENCES
| [1] | K. M. Sadiq J. Zarrouk, “Geothermal Well”. |
| [2] | P. Allahvirdizadeh, “A review on geothermal wells: Well integrity issues”. |