Unveiling the Depths- A Novel of Successful Story of First 61% H2S Well Drilled Ever in the Gulf Area
Authors: Valappil Suhail , John Jaim , Al Jabery Razan , Piskulin Ivan , Zgabaia Claudiu , Tayab Muhammad , Unnikrishnan Nitheesh , Kareem Asif Abdul , Raju Padiyara , Crasta John , Mulla Akhlaq 
Published: November 2024

This paper presents a detailed analysis of a well drilled with 61% of H2S with ∼10 km radius of risk contour, focusing on the well control complications and challenges due to the high sour nature of the well. Given the high H2S content, this poses critical challenges to the planning and preparation of the wells in terms of high-risk coring, logging operations and associated challenging well planning, Material selection and emergency response planning (ERP). Advanced modeling techniques (such as PHAST model) were employed to outline the risk contours and identify critical receptors within emergency planning zone (76 PPM contour), emergency awareness zone (10PPM contour). The risk study revealed the implications of these findings on emergency response planning. Key recommendations were provided to ensure monitoring, risk mitigation, and stakeholder communication to address the challenges associated with ∼10 km radius. MAH (Major accidents hazard) associated with critical event "Well control" in such high temperature high pressure high sour wells and all possible scenarios of receptor interactions are analyzed in detail to ascertain critical risks. The derived fault and event tree analysis constitute prime tools capable of identifying and risk assessing potential failures from critical events. A well control exercise associated with high H2S release was simulated to analyze critical path and identify root cause with help of Bayesian model. The control parameters for drilling the well were accordingly set based on learnings from past incidents and expert elicitation data.

A study of critical events and risk mitigation measures forming a defined framework was developed to approach drilling of the ultra-high H2S well. Key receptors including residential areas, ecological zones, and critical construction projects, permanent residentials camps were mapped. The potential exposure levels for these receptors were assessed to determine the severity of impact. The modeling results indicated that the largest risk contour extends to 10 kilometers from the well site. Within this area, H2S concentrations exceed the 10 PPM limit which is occupational exposure requirements that demanded requirement of unconventional methodology to mitigate accidental H2S release. The control barriers all had their own independent material associated limitations against the high H2S concentration. An innovative approach with experience in similar scenarios coupled with detailed risk analysis equipped overcoming the challenges. The practical implementation of the decision tree ensured successful drilling of two such high H2S sour gas wells in the same field with minimum H2S impact. The paper also proposes the HSE framework for safe well delivery for the high H2S wells and improving the risk barriers with regards to potential impact of H2S release. key receptors including residential areas, ecological zones, and critical construction projects, permanent residentials camps were mapped. The potential exposure levels for these receptors were assessed to determine the severity of impact. The modeling results indicated that the largest risk contour extends to 10 kilometers from the well site. Within this area, H2S concentrations exceed the 10 PPM limit which is occupational exposure requirements. To mitigate the identified risks, the paper recommends a multi-risk mitigation approach:

Enhanced H2S detection and monitoring systems Comprehensive training for personnel Development of evacuation plans for nearby communities. Collaboration with local authorities and stakeholders

This well drilling risk management program shall be a navigational reference and can determine new dynamics for exploring similar types of wells with high potential sensitive receptors delivering least impact in societal risk. Additional engineering measures were taken to address the sub-surface challenges that were once perceived to be unapproachable. Paving new horizons to breach deeper barriers, many methodologies used in these wells were a first in terms of equipment planning and operational methodology.