Cálculo de costos

Once data from geological studies and seismic surveys can confirm a hydrocarbon prospect for a field, a well is drilled to examine the economic viability of field (Smit et al. 2010). All drilling operations are mostly conducted to meet three basic objectives: to provide a fit for purpose well, to ensure that health, safety and environmental (HSE) work procedures are adhered to, and to minimize overall well cost (Payne et al. 1994). Of these objectives, cost control appears to be the most crucial as failure manage it affects project budgets, future projects investment among many others (Payne et al. 1994, British Petroleum 2010, and Smit et al. 2010). Hence proper measures and safety standards are employed in oil and gas drilling operations to achieve this crucial objective while addressing the other two mentioned. Similar to other oil and gas drilling operations, the offshore deep-water drilling has two stages of drilling. The first is running and cementing of cases while the second is drilling until the drill bit reaches the depth of the targeted zone (Payne et al. 1994, British Petroleum 2010, and Smit et al. 2010).

The two stages of drilling are somehow intertwined and overlapping in each of the stages until the final well is completed. Running a drilling operation begins with the preparation and setting up of the field with the aid of appropriate equipment such as drill ship, accommodation for crews, electricity, water and all the auxiliary items needed for successful drilling (Aven and Vinnem 2005). Offshore exploration and

22| P a g e development wells are usually drilled from moveable offshore drilling units and depending on the water depth and remoteness of the location, these "rigs" may be jack- ups (up to 4000 feet of water), or semisubmersibles, or drill ships (up to 12,000 feet of water). Jack-ups are bottom-supported units while semisubmersibles and drill ships are floating units (Aven & Vinnem 2005, and Diamond Offshore 2014). The figure 2- 1 below shows the different types of rigs that can be used for drilling activities in the offshore deep-water sector.

Figure 2-1: Offshore deep-water rigs (Rondini 2010)

When an appropriate rig is selected based on location, geology of the field and stipulated budget for the project, the drill crew immediately commence drilling by making a starter hole (Williams 2011). Drill bit, collar and drill pipe are placed in the starter hole for the actual drilling operation to begin (Williams 2011). A Blow-Out

23| P a g e Preventer (or “BOP”) is installed on top of the casing head before drilling takes place. The BOP has high-pressure safety valves designed to seal off the well and block any escaping gases or liquids from the hole beneath in order to prevent a blow-out from occurring (Williams 2011). As drilling progresses, mud is circulated through the pipe and out of the bit to float the rock cuttings out of the hole and new joints are added to the drill pipes as the hole gets deeper. When pre-set depth is reached, casing pipe is placed in the hole for cementing to commence to avoid oil and gas leakages (DeRosa 2013). Finally, the cement is allowed to harden and then tested for such properties as hardness, alignment and a proper seal (Speight 2015). For pictorial purposes, the figure 2-2 below portrays a typical well with pipeline, casing tube and several cementing stages in an offshore deep-water drilling process.

24| P a g e For the drilled well to be ready for usage other important activities need to be undertaken. Such as pumping mud into the hole in order to separate all debris from plugging the well hole. Additionally, mud system equipment such as de-sanders, de- silters and de-gassers are positioned in the well hole to remove smaller particles and gas from the well (Speight 2015). Although the process involved in oil and gas drilling seems quite linear from a theoretical point of view, the increasing risk and uncertainties associate with the operations is what often result in cost overrun for most drilling projects (Abimbola et al. 2014, Ismail et al. 2014, and Speight 2015). The more operational delays there are, the more the drilling cost incurred. Most drilling rigs operate 24 hours per day, 7 days per week and rig crews’ work 8 or 12-hour shifts in rotations that last anywhere from one to four weeks or more, depending on the location (Ismail et al. 2014). This pattern of work should be continuous without any distractions until drilling is completed as any adverse effect on the smooth running of the drill has a cost implications attached by extension.

Having discussed the offshore drilling process and highlighted some of the factors that escalate costs, it is equally vital to explain and discuss the risks that surround oil and gas operation as well. Hence the next section discusses and evaluates the different types of risks and complexities associated with offshore drilling activities. This will clearly set the stage to critically evaluate and review the past cost models and help direct the development of the validated model the research seeks to achieve. The next section on risks and complexities will help to comprehensively assess and evaluate the capabilities of past models to handle cost overruns under the given requirements and risk conditions in the offshore drilling industry and would further provide proofs of the gaps the research intents to address.

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