Contingency Planning for Drilling and Producing High-Pressure Sour-Gas Wells
Authors: Hamby T.W. , Smith J.R. 
Published: December 2007

A blowout of a sour-gas well near a populated area can expose local residents to hazards that are not normally associated with a blowout of an oil or gas well. Without detailed plans made well in advance and kept current, such an accident can have serious consequences for a company that is not prepared.

Introduction
Field experience in developing the sour-gas reserves discovered in Western Canada in the early 1950's showed that metals often failed quickly when exposed to sour gas because of its hydrogen sulfide (H2S) content. For a time there was considerable concern about the industry's ability to provide facilities that could safely handle this gas, but research by both industry and universities developed the necessary technology, and today sour-gas production and processing in this area is a safe, routine operation. This achievement can be attributed, for the most part, to the careful selection, quality control, and inspection of materials scheduled for use in sour-gas service.
Now once again the industry is faced with a new challenge for producing sour gas. Drilling for and producing from deep, high-pressured reservoirs of producing from deep, high-pressured reservoirs of high H2S content present a hazard not normally associated with the production of sour gas from moderately pressured reservoirs. This is the threat of blowouts caused by the often rapid failure of high-strength steels when they are exposed to hydrogen sulfide. When H2S is Present, the yield strength of steel must be limited to about 90 to 100 ksi and stringent quality control and inspection procedures must be set up to insure that higher strength materials are not used to drill or complete the well. In spite of all possible precautions, there will always exist the possibility that failure of some component during the possibility that failure of some component during the lifetime of a well may lead to a blowout with disastrous results. When a blowout occurs in an ultra-deep well, much time may be required to control it if relief wells must be drilled. Thus if the well does not bridge or the reservoir does not deplete quickly, the operator will be faced with protecting the lives and property of nearby residents for an extended period. This is particularly serious when the period. This is particularly serious when the blowout occurs near a heavily populated area.
We shall discuss here various elements that Shell considered in developing contingency plans for its deep Smackover drilling program in Mississippi. The actual plans are quite detailed and outline the responsibilities and duties of all concerned, from top management to the field operations personnel. They are divided into two parts, one dealing with procedures for protecting the operating personnel, and the other outlining means for protecting nearby residents and their property. The execution of the latter is primarily the responsibility of the staff organization; primarily the responsibility of the staff organization; however, the field operating personnel are responsible for the production of any endangered residents until the staff group relieves them of this function. The plans are principally designed to cope with the period of shock that immediately follows an accident, when there is the greatest danger of losing control of the situation.

General Considerations
Contingency plans must be specific in assigning duties and areas of responsibility, so that each man knows what is expected of him during an emergency.
JPT
P. 347