Offshore drilling

Whether onshore or offshore drilling is carried out, the basic drilling system employed in both cases will be the rotary rig (Fig. 3.7) and the following summarises the basic functions and parts of such a unit. Three basic functions are carried out during rotary drilling operations ... 

Foam Control. Whereas some siUcones are known to be foam promoters, Dow Corning FS-1265 Fluid is a Hquid fluorosiUcone with effective antifoam properties. Petroleum industry appHcation of fluids and dispersions in gas—oil separators on offshore drilling platforms has been successful. Their use peaked in the early 1980s, coinciding with constrained cmde oil capacity and production. Diesel fuels are an excellent solvent for dimethyl silicones and render them ineffective as an antifoam. A new antifoam which does not require the use of added siUca is formulated from a fluorosiUcone copolymer. It has shown promise to antifoam (8) diesel fuel (see Defoamers). 

Other regulations apply in different offshore drilling areas in the United States and around the world. AH have had a profound effect on drilling fluid technology (169,170). Very few instances of water-base muds failing the mysid bioassay test exist in the 1990s. Operators and service companies have eliminated use of the mote toxic additives, reformulated old mud systems, and developed new ones to ensure acceptable environmental performance based on pertinent regulations. 

Figure 5.10 shows a detailed fault tree for an offshore drilling operation. The top event of the fault tree is Failure to use shear rams to prevent blowout. As wi the fault tree in Figure 5.2, the representahon combines both hardware... 

FIGURE 5.10. Offshore Drilling Blowout Fault Tree Subtree, "Fail to use shear rams to prevent blowout." 221... 

Height is the vertical distance from ground or water surface to the center of area. The shape coefficient C, for a derrick is assumed as 1.25. and were obtained from ABS, Rules for Building and Classing Offshore Drilling Units, 1968. ... 

Common salt, or sodium chloride, is also present in dissolved form in drilling fluids. Levels up to 3,000 mg/L chloride and sometimes higher are naturally present in freshwater muds as a consequence of the salinity of subterranean brines in drilled formations. Seawater is the natural source of water for offshore drilling muds. Saturated brine drilling fluids become a necessity when drilling with water-based muds through salt zones to get to oil and gas reservoirs below the salt. 

Air and gas, unstable foam and stable foam techniques are used almost exclusively for onshore drilling operations, rarely in offshore applications. Aerated mud, however, is used for both onshore and offshore drilling operations. 

However, dilution can lead to added costs of mud-treating materials such as weighting materials and other chemical additives. In addition, disposal of excess drilling fluid can create problems on offshore drilling projects. 

Offshore drilling vessels are classified as either bottom-supported or floating-type vessels. Water depth is generally the governing factor as to which type of vessel is employed. 

The most fundamental difference found between onshore and offshore drilling occurs when the wellhead is located at the seafloor. This configuration makes communication with the well more complex. A marine riser provides communication and circulation capability between the surface and the seafloor, and is used at some point during most offshore drilling. The riser consists of large-diameter (17-20) in.) steel pipe joints of approximately 50-ft lengths, with quick-connect couplings. The riser can be connected at the seafloor to a wellhead or to a subsea blowout preventer stack. A diverter system is usually attached at the... 

Candler, J., et al., Source of mercury and cadmium in offshore drilling discharges, SPE Drilling Engineering December, 1992. 

A. Ayers, R. C., Jr., et al., The generic mud concept for NPDES permitting of offshore drilling discharges, J Petroleum Engineering March 1985. 

Offshore drilling costs may exceed similar land operations by 30 to 40 times and hence it is important to be able to minimize the overall drilling time. This is accomplished through mathematical modeling of the drilling penetration rate and operation (Wee and Kalogerakis, 1989). 

Wee and Kalogerakis (1989) tested the above models using Canadian offshore well penetration data (offshore drill operated by Husky Oil). Considerable effort was required to convert the raw data into a set of data suitable for regression. The complete dataset is given in the above reference. 

Offshore Drilling or Production Facility Hydrocarbon Fire MPS Smoke Heat Optical APIRP 14 G NFPA 30, Section 5-5.5.1. 

A small crack develops in an underwater pipe that carries oil from an offshore drilling rig to a holding tank on land. Crude oil seeps out of the crack and into the ocean, where marine plants and animals are exposed to its toxic effects. 

Smit, M.G.D., Jak, R.G., Rye, H., Frost, T.K., Singsaas, 1. and Karman, C.C. (2008). Assessment of Environmental Risks from Toxic and Nontoxic Stressors A Proposed Concept for a Risk-Based Management Tool for Offshore Drilling Discharges. Integrated Environmental Assessment and Management 4(2) 177-183. 

Gefliff, J., Roach, A. Toyo, J., and Carpenter, J. (1997) An overview of the environmental benefits of LAO based drilling fluids for offshore drilling. Presented at the 5th IBC International Conference on Minimising the Environmental Effects of Drilling Operations Aberdeen, June 1997. 

Offshore Drilling. When exploration moves offshore, standard drilling equipment obviously must be supplemented by some sort of structure that provides a stable platform for operations. The structure also must be movable, given the odds against a single wildcat finding commercial quantities of petroleum. 

Fig. 23. Fixed-leg offshore drilling and production platform of the "steel jacket ...

In the past, hydrates have been associated with significant movement of earth (seafloor slumps) in deepwater ocean environments. Notably, Bugge et al. (1988), Schmuck and Pauli (1993), MacDonald et al. (1994), and Pauli and Dillon (2001) have described both large and small Earth movements associated with hydrates. Concerns have been expressed (Campbell, 1991) about the effect of hydrates on foundations of platforms and pipelines, as well as offshore drilling. Hydrates as geohazards are discussed in Section 7.8. 

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