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05/18/08 |
Drilling the wellAll of the efforts of the petroleum landmen, geologists, and geophysicists, and everyone else involved in leasing and exploration activities up to this point must culminate in a decision by the management of the petroleum company to either drill or not drill a well. If the exploration activities conducted thus far have not found encouraging indications for the accumulation of petroleum in the area being explored, the leases held in the area will likely be dropped. If exploration activities have been encouraging, however, a decision will likely be made to drill an exploratory well. Such a decision may require the commitment of hundreds of thousands or even millions of dollars for the drilling program. In this section we will discuss the activities related to the drilling of an exploratory well. State regulations regarding drilling, development, and production will be discussed in a subsequent section.Drill-site selectionThe selection of the drill site is based largely on the geological evidence indicating the possible accumulation of petroleum. The exploration company will want to drill the well at the most advantageous location for the discovery of oil or gas. Surface conditions, however, must also be taken into consideration when selecting the drill site. There must be a nearly level area of sufficient size on which to erect the drilling rig, excavate reserve pits, and provide storage for all of the materials and equipment that will be required for the drilling program. All of the required legal matters need to have been attended to, such as acquiring a drilling permit, surveying of the drill site, and so on. When all of these matters have been resolved, the work on site preparation will begin.Drill-site preparationOnce the drill site has been selected and surveyed, a contractor or contractors will move in with equipment to prepare the location. If necessary, the site will be cleared and leveled. A large pit will be constructed to contain water for drilling operations and for the disposal of drill cuttings and other waste. A small drilling rig, referred to as a dry-hole digger, will be used to start the main hole. A large-diameter hole will be drilled to a shallow depth and lined with conductor pipe. Sometimes a large, rectangular cellar is excavated around the main bore hole and lined with wood. A smaller-diameter hole called a "rat hole" is drilled near the main bore hole. The rat hole is lined with pipe and is used for the temporary storage of a piece of drilling equipment called the "kelly." When all of this work has been completed, the drilling contractor Will move in with the large drilling rig and all the equipment required for the drilling of the well.Rigging upThe components of the drilling rig and all necessary equipment are moved onto the location with large, specially equipped trucks. The substructure of the fig is located and leveled over the main bore hole (fig. 22). The mast or derrick is raised over the substructure and the other equipment such as engines, pumps, and rotating and hoisting equipment are aligned and connected. The drill pipe and drill collars are laid out on racks convenient to the rig floor so that they may be hoisted up when needed and connected to the drill bit or added to the drill string. Water and fuel tanks are filled. Additives for the drilling fluid (drilling mud) are stored on location. When all these matters have been attended to, the drilling contractor is ready to begin drilling operations (spud the well).Figure 22--A drilling rig with its major components and related equipment.
Spudding in"Spudding in," or to "spud" a well, means to begin drilling operations. The drill string, consisting of a drill bit, drill collars, drill pipe, and kelly, is assembled and lowered into the conductor pipe. Drilling fluid, better known as drilling mud, is circulated through the kelly and the drill string by means of pipes and flexible hose connecting the drilling fluid or mud pumps and a swivel device attached to the upper end of the kelly. The swivel device enables drilling mud to be circulated while the kelly and drill string are rotated. The mud pump draws fluid from mud tanks or pits located nearby. The drilling mud passes through the kelly, drill pipe, drill collars, and drill bit. It is returned to the surface by means of the well bore and the conductor pipe where it is directed to a device called a shale shaker. The shale shaker separates the drill cuttings and solids from the drilling mud, which is returned to the mud tanks to be circulated again (fig. 23). As the drill string is rotated in the well bore, the drill bit cuts into the rock. The drilling mud lubricates and cools the drill bit and drill string and carries the drill cuttings to the surface (fig. 23).Figure 23--Diagram illustrating the drilling-fluid (drilling-mud) system and the flow of fluids through the system.
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