沖擊回轉鉆進技術空氣及天然氣鉆井翻譯(編輯修改稿)

　

【文章內容簡介】 p (see Figure 15) to the mud pit. The drilling water is pumped from the pit, through the pump, through an onboard pipe system, through the rotary hose, through the hydraulic tophead drive, down the inside of the drill pipe, and through the drill bit to the bottom of the well. The drilling water entrains the rock cuttings from the advance of the bit and carries the cuttings to the surface via the annulus between the outside of the drill pipe and the inside of the borehole. At the surface the drilling fluid (water) from the annulus with entrained cuttings is returned to the pit where the rock cuttings are allowed to settle out to the bottom. The pumps on single drilling rigs are small positive displacement reciprocating piston or centrifugal type. 論文翻譯 10 Figure 17 shows a detailed schematic of a direct circulation pressed air drilling system that would be used on a typical double or triple drilling rig. Direct circulation requires that atmospheric air be pressed by the pressor and then forced through the standpipe on the mast, through the rotary hose, through the swivel and down the inside of the kelly, down the inside of the drill pipe and drill collars, through the drill bit (at the bottom of the borehole) into the annulus space between the outside of the drill string and the inside of the borehole. The pressed air entrains the rock bit cuttings and then flows with the cuttings up the annulus to the surface where the pressed air with the entrained cuttings exit the circulation system via the blooey line. The pressed air and cuttings exit the blooey line into a large pit dug into the ground surface (burn pit). These pits are lined with an impermeable plastic liner. 論文翻譯 11 In order to safely drill boreholes to these deposits heavily weighted drilling muds are utilized. The heavy fluid column in the annulus provides the high bottomhole pressure needed to balance (or overbalance) the high pore pressure of the deposit. Figure 113 also shows that the heavier the drilling fluid column in the annulus the more useful the drilling fluid is for controlling high pore pressure (the arrow points downward to increasing capability to control high pore pressure). There are limits to how heavy a drilling mud can be. As was discussed above, too heavy a drilling mud results in overbalanced drilling and this can result in formation damage. But there is a greater risk to overbalanced drilling. If the drilling mud is too heavy the rock formations in the openhole section can fracture. These fracturescould result in a loss of the circulating mud which could result in a blowout. 論文翻譯 12 In the past decade it has been observed that drilling with a circulation fluid that has a bottomhole pressure slightly below that of the pore pressure of the fluid deposit gives near optimum results. This type of drilling is denoted as underbalanced drilling. Underbalanced drilling allows the formation to produce fluid as the drilling progresses. This lowers or eliminates the risk of formation damage and eliminates the possibility of formation fracture and loss of circulation. In general, if the pore pressure of a deposit is high, an engineered adjustment to the drilling mud weight (with additives) can yield the appropriate drilling fluid to assure underbalanced drilling. However, if the pore pressure is not unusually high then air and gas drilling techniques are required to lighten the drilling fluid column in the annulus. Figure 114 shows a schematic of the various drilling fluids and their respective potential for keeping formation water out of the drilled borehole. Formation water is often encountered when drilling to a subsurface target depth. This water can be in fracture and pore structures of the rock formations above the target depth. If drilling mud is used as the circulating fluid, the pressure of the mud column in the annulus is usually sufficient to keep formation water from flowing out of the exposed rock formations in the borehole. The lighter drilling fluids have lower bottomhole pressure, thus, the lower the pressure on any water in the exposed fracture or pore structures in the drilled rock formations. Figure 114 shows that the heavier drilling fluids have a 論文翻譯 13 greater ability to cope with formation water flow into to the borehole(the arrow points downward to increasing control of formation water). Flow Characteristics A parison is made of the flow characteristics of mud drilling and air drilling in an example deep well. A schematic of this example well is shown in Figure 115. The well is cased from the surface to 7,000 ft with API 8 5/8 inch diameter, lb/ft nominal, casing. The well has been drilled out of the casing shoe with a 7 7/8 inch diameter drill bit. The parison is made for drilling at 10,000 ft. The drill string in the example well is made up of (bottom to top), 7 7/8 inch diameter drill bit, ~ 500 ft of 6 3/4 inch outside diameter by 2 13/16 inch inside diameter drill collars, and ~ 9,500 ft of API 4 1/2 inch diameter, lb/ft nominal, EUS135,NC 50, drill pipe. 論文翻譯 14 The mud drilling hydraulics calculations are carried out assuming the drilling mud weight is 10 lb/gal (75 lb/ft3), the Bingham mud yield is 10 lb/100 ft2, and the plastic viscosity is 30 centipose. The drill bit is assumed to have three 13/32 inch diameter nozzles and the drilling mud circulation flow rate is 300 gals/minute. Figure 116 shows the plots of the pressures in the inpressible drilling mud as a function of depth. In the figure is a plot of the pressure inside the drill string. The pressure is approximately 1,400 psig at injection and 6,000 psig at the bottom of the inside of the drill string just above the bit nozzles. Also in the figure is a plot of the pressure in the annulus. The pressure is approximately