Dr. Hans-Joachim Uth, Process Plant Safety Expert, Lychen
This study examines the risks associated with
- the surface technical installations at the well site,
- the transport of environmentally hazardous substances on the road and in pipelines, and
- the technical design of the wellbore
that can occur during specified normal operation and any deviations therefrom (accident).
The purpose of the study, based on worst case scenarios, is to determine the accident prevention and reduction measures needed to meet the state of the art. Once these measures have been established, they are compared with the technical and organisational precautions in place in a typical facility in order to find out whether they are suitable and complete. The investigations are based on information and documents supplied by ExxonMobil Production Deutschland GmbH (EMPG) and on the available literature. No on-site investigation of a specific installation was carried out.
The worst case scenario is a widely employed approach in high-risk technology. A description of the maximum possible impact is equivalent to ascertaining the upper end of a scale comprising all the safety measures. In an iterative process the conditions that lead to a worst case scenario are systematically eliminated by technical and organisational measures. This produces scenarios with shrinking effects. At the same time, the likelihood of scenarios with ever smaller impacts increases. The point of departure is the release, explosion and burning of the entire surface stock of hazardous substances at the well site. Scenarios are then developed with ever smaller amounts of hazardous substances resulting from the graded effectiveness of the technical and organisational means employed. No analysis of the causes of the assumed incident is undertaken in this scenario-based approach. In the evaluation of the scenario, however, the measures taken play a key role in averting the causes of an incident, such as traffic, installation and environmental safety hazards, and in preventing deliberate interventions by unauthorized third parties. Should several hazardous substances be involved, a main substance principle is used. In this case the overall amount of all the hazardous substances involved is calculated as the amount of the main substance. The main substance is the substance with the greatest impact. Eight main scenarios and 29 sub-scenarios are modelled and an assessment made of the likelihood that they will occur and of the effects they will have. The incidents with the biggest impact on people and the environment are blow-outs of natural gas (sour gas), the burning of the entire stocks of diesel fuel stored at the well site for operational purposes and the release during transport of large amounts of substances that are hazardous to the environment. A description is provided of the ‘state of the art’ and ‘good management practice’ of the precautions that are taken to prevent major accidents and to limit their impact at well sites. These are then compared with standard practice and an assessment is made. Practical experience in the sector is supplemented by an analysis of the accident reports in the past. The comparison enables conclusions to be drawn as to how protection of people and the environment can be improved. Closed systems and cycles should be deployed in fracking as a matter of principle. When using frac fluids, there should be strict observance of the most stringent requirements in handling substances hazardous to water that are listed in Water Hazard Class 2 (F2 +R2+ I1 +I2, as defined in the German Ordinance on Installations for Handling Substances Hazardous to Water(VAwS). Pipelines for the transport of natural gas and flow lines for the transport of backflow / adhesive water must fully satisfy the requirements of the German High Pressure Gas Pipeline Ordinance (GashochdruckleitungV) and the German Pipeline Ordinance (RohrFLtgV) respectively. The safe use of existing (old) wellbores for fracs would only appear justifiable after pressure and leak tests have been carried out and the integrity of the cement has been verified. The investigations indicate that every frac should be preceded by wellbore measuring routines as well as cementation up to 300 metres below the lower limit of the ground water horizon. A limitation of the use of environmentally compatible frac fluids would also help to enhance safety . Adherence to underground safety distances between the fracked horizons would also be a suitable way of excluding unwanted interactions. The analysis of the safety management system reveals deficits in modern safety cultures (possible improvements on the basis of recommendations made by the German Commission on Process Safety, for example). Quality assurance of the well integrity is a critical component and, as a rule, should be undertaken by third parties (experts). In a risk analysis the generic approaches should be supplemented in individual cases by case procedures and the use of systems analysis methods. Standardised safety analyses for typical procedures and installations, such as drilling, fracking, extraction, gas treatment, backflow / adhesive water treatment, are a possible source of improvement. In this connection the systematic collection of failure rate data is advisable in order to pave the way for the use of quantitative methods (quantitative risk assessment). Emergency management is improved by the use of a specific hazard management system as defined in SFK-GS-45 issued by the German Commission on Major Accidents (Störfallkommission). The well sites should be designed in accordance with the requirements of the Fire Fighting Water Retention Guideline and the interface between the company and public emergency response planning should comply with the recommendations of the Federal Ministry of the Environment. An improvement in risk communication in operational practice enhances overall safety too.
