Auditing Offshore Safety Risk Assessments
Authors: Moss Thomas R. 
Published: December 2007

Risk assessments submitted to support proposals for offshore operations mustbe audited to ensure conformance with regulating authorities' safetyrequirements. This paper outlines the approach adopted by RM Consultants (RMC)Ltd. for auditing recent submissions to the U.K. Dept. of Energy forsimultaneous drilling and production (SDP) with jackup rigs cantilevered overgas production platforms. The principles are valid for risk-assessment auditsof other offshore installations.

"The probability of occurrence must be estimated for each hazardousevent that is likely to harm personnel, the environment, or the installation. This process involves developing the logical relationships among the initiatingevents and combining these to estimate the accident probability."

Introduction

Probabilistic risk assessment (PRA) to Probabilistic risk assessment (PRA)to evaluate the potential for major accidents in offshore operations isgenerally accepted in the U.K. and Norway as a powerful technique for improvingsafety. It involves an analysis of the proposed operations to identifypotentially hazardous situations and further detailed studies to quantify theprobability and consequences of each unwanted probability and consequences ofeach unwanted event. Based on the results, measures can generally be introducedto improve the safety of the installation substantially.

SDP

"SDP" refers to such operations as tubing workovers performedsimultaneously with production. The U.K. authorities have production. The U.K.authorities have always had reservations regarding SDP because two hazardousactivities performed concurrently and in proximity are potentially morehazardous than either activity performed alone. Nevertheless, operators ofperformed alone. Nevertheless, operators of integrated drilling and productioninstallations in the oil province practice SDP and have always convinced theauthorities that such operations are safe. In the gas province, however, theposition is different. On the older gas platforms, the integrated drillingfacilities have been removed; operators use temporary package rigs or jackupsto drill and repair gas wells. The work is generally concentrated in thelow-demand period, with the platform shut down and the wells plugged downhole. Newer gas platforms have been built without integrated drilling facilities, sooperators also use jackups for drilling and workover on these platforms. Inthese cases, the drilling rig is cantilevered over the main platform, anddrilling or workover occurs from platform, and drilling or workover occurs fromthe jackup through slots in the wellhead platform. platform. Neither platformnor jackup is designed with the other installation specifically in mind. Therefore, a range of special problemssuch as the complicated managementproblemssuch as the complicated management of two hazardous activities;temporary integration of power, control, and safety equipment; and thevulnerability of the twinned installation to a major hydrocarbon releaseneed tobe considered. Consequently, the Dept. of Energy requested a PRA with properlyconducted hazard and operability properly conducted hazard and operabilitystudies (HAZOP's) and a hazard analysis (HAZAN) to support any proposalinvolving such special operations as SDP.

PRA PRA PRA involves identification of all possible PRA involvesidentification of all possible things that can go wrong on an installation andthe characterization of these events to quantify the risks. The assessmentresults are compared with target results based on past experience. If thepredicted risks are past experience. If the predicted risks are unacceptable, then efforts are directed toward risk reduction. This can be achieved byreducing the consequences of the major hazards or by reducing the probabilitiesof their occurrence. The two main risk-assessment techniques are HAZOP andHAZAN. These involve different phases of the risk-assessment process, whichtypically includes the following process, which typically includes thefollowing stages:identification and ranking of for hazards,evaluationof consequences of each potentially hazardous event,quantification ofprobability of each event,comparison of risks (consequences andprobabilities) against threshold of acceptability, andintroduction ofmeasures to reduce risks in areas where hazards are unacceptably high.

Hazard Identification.

Safety-related hazards are identified by use of checklists based on accidentstatistics, experience in the industry, and HAZOP's. Hazards can he eitherresults of external causes or process-related. A checklist of external hazardsnoted by the Norwegian Petroleum Directorate for offshore Petroleum Directoratefor offshore installations includes blowouts, fires and explosions, fallingobjects, ship and helicopter collisions, earthquakes, extreme weatherconditions, other possible relevant types of accident, and relevantcombinations of these accidents. These hazards clearly need consideration inany risk assessment of SDP.

JPT

P. 1241