Thorough well planning is essential to provide safe and efficient drilling of wells penetrating hydrogen sulfide bearing formations. Such planning requires an understanding of the problems which can result from the presence of hydrogen sulfide, selection of equipment suitable for use in H2S environments, and training of personnel to work safely around hydrogen sulfide. Through proper planning, problems associated with drilling in planning, problems associated with drilling in areas encountering hydrogen sulfide can be minimized.
This paper covers several areas of additional planning required for H2S wells which differ from planning required for H2S wells which differ from requirements for non-H2S wells. Items to be discussed include personnel safety, drilling fluids, tubular goods, blowout preventers, wellhead equipment, and general H2S well planning considerations.
Today's high drilling costs make proper well planning important for all wells. Drilling in planning important for all wells. Drilling in formations containing hydrogen sulfide requires even more planning to overcome problems associated with this poisonous gas.
A colorless gas with a specific gravity of 1.192, hydrogen sulfide is extremely toxic, is corrosive, and causes sulfide stress cracking (SSC) in many of the high strength steels commonly used in drilling operations. At low concentrations it has an odor comparable to rotten eggs; at higher concentrations an odor may not be detected because the sense of smell may be deadened. The high specific gravity of H2S causes it to settle and accumulate in low lying areas. These properties make hydrogen sulfide an extremely hazardous material and emphasize the need for careful planning in drilling H2S bearing formations. Areas in which additional planning is required include personnel safety, drilling fluids, tubular goods, blowout preventers, wellhead equipment, and general H2S preventers, wellhead equipment, and general H2S well planning considerations.
PERSONNEL SAFETY PERSONNEL SAFETY Personnel safety is the prime consideration when planning a hydrogen sulfide well. Table 1 presents a summary of physical effects of various presents a summary of physical effects of various concentrations of hydrogen sulfide. In low concentrations, H2S causes eye irritation, headaches, nausea and other symptoms. Concentrations in the range of 500–700 ppm can cause death. On an 8-hour time weighted average basis, the maximum acceptable exposure concentration is 20 ppm.
Providing breathing equipment and training personnel in its use and maintenance is an personnel in its use and maintenance is an important segment of well planning. Table 2 provides a list of safety equipment needed on provides a list of safety equipment needed on a typical drilling location. Outside safety consultants can be used to handle training and to assist in maintaining the safety equipment. Wearing the equipment during short work sessions and regular onsite safety training sessions are valuable aids in obtaining adequate crew familiarity with the equipment.
A continuous monitoring system consisting of several strategically placed detectors is necessary to detect any H2S at the surface. The system should be equipped with a low H2S concentration (10 ppm) visual warning and an audible warning when a high concentration (20 ppm) of H2S is detected. Each continuous monitoring detector should be tested and calibrated on a regular basis. Hand held detectors can be used for spot checks.
A hydrogen sulfide contingency plan is required by the Texas Railroad Commission for all wells where the concentration of hydrogen sulfide in the system is 100 ppm or greater.