Managing 23% H2S during Appraisal Well Drilling & Testing Operations in an Area with Adjacent Population and Infrastructure
Authors: Burt Ian , Susanna Louis 
Published: November 2015

Objectives/Scope

While planning to drill a high pressure, high temperature, and high H2S gas appraisal well in the coastal area of Abu Dhabi, data from four previous offset wells showed that 23% H2S was likely to be present in several formations. Gas dispersion modelling and risk analyses were studied to determine the possibility of drilling an appraisal well at an onshore location. The preferred onshore area is adjacent to some populated areas and existing infrastructure, such as private housing, a highway, and government facilities.

Methods, Procedures, Process

A large part of the approved mandatory HSEIA document was taken up by the Quantitative Risk Assessment (QRA) section, including gas dispersion modelling to determine the consequences of numerous gas release scenarios. Most of these gas release scenarios were related to well test activities. The modelling results allowed worst case scenarios to be determined and levels of risk could also be established from the modelling results. In addition, the ADNOC individual risk requirements were applied to determine the Emergency Planning Zone (EPZ). Concurrently, an alternative offshore location was chosen, for which a second HSEIA document was developed, to be used in case the QRA indicated that onshore drilling would not be viable due to any unacceptable high level of risk that may exist in areas around the planned wellsite. These areas could potentially include or impact upon sections of the local population and infrastructure as previously mentioned.

Results, Observations, Conclusions

The QRA indicated that it was possible to utilize the onshore option. The exact wellsite location was chosen primarily on the high priority given to the safety of the general population in the area and with due regard to the location and nature of existing infrastructure. Strict procedures and processes were developed, agreed, and implemented to fully control access in the EPZ. Comprehensive H2S services and management procedures were developed and implemented on the rig and wellsite as well as the surrounding area of the EPZ and beyond. This included multiple gas detection monitors at various locations on the rig, around the wellsite and perimeter fencing, within the EPZ and on the EPZ perimeter, and beyond the EPZ towards the highway. In addition public awareness alarms were positioned towards the general population housing areas and numerous multiple language warning signs placed in strategic locations. Breathing air loop systems and escape breathing apparatus and equipment has been utilized throughout the wellsite and for all personnel entering the EPZ. Use of this equipment has been backed up with comprehensive third party certified training, extensive site training, and practical drills and exercises to ensure individual understanding of the equipment used. Operationally, well test activities were limited to certain weather conditions and parameters. Numerous meetings and intensive discussions took place with relevant authorities and local stakeholders, to inform them of our operational plans and how to act in case of any emergency. Shortly after well spud date a large scale emergency exercise was conducted, with involvement of all site personnel, Abu Dhabi emergency personnel, relevant authorities, 3rd parties, and local stakeholders.

Innovations

Constant monitoring of operational requirements and review of equipment and management processes has been ongoing throughout the project. The local population, police, and other relevant stakeholders have been fully informed of operational intent and controls. A dedicated H2S services roaming vehicle was specially commissioned and adapted to meet the needs of system and equipment checks in field. This vehicle is fitted with gas detection systems and alarm PA systems to alert the public of any pending hazards or warnings. Emergency response procedures were discussed and agreed with interested parties at all levels to ensure an adequate tiered response to any emergency scenario. Public awareness meetings, information leaflets and local media notifications have all been utilized to assure stakeholders of safe operations and suitable emergency response. A dedicated public help line was set up to answer any questions or concerns from interested parties.