Mud Pumps

To reduce drilling and development costs, slimhole drilling is increasingly being used. Slimhole wells are considered wells in which at least 90 percent of the hole has been drilled with a bit fewer than six inches in diameter. For example, a typical rig uses a 8.5-in bit and a 5-in drill pipe, whereas a slimhole rig may use a 4-in bit and a 3.7-in drill pipe. Slimhole drilling is especially valuable in economically marginal fields and in environmentally sensitive areas, since the fuel consumption can be 75 percent less (mud pumps, drill power), the mud costs 80 percent less, the rig weight is 80 percent less, and the drill site is 75 percent smaller. 

Pump Installation 627. Pump Operation 630. Pump Performance Charts 631. Mud Pump Hydraulics 631. Useful Formulas 645. 

Mud pumps consume more than 60% of all the horsepower used in rotary drilling. Mud pumps are used to circulate drilling fluid through the mud circulation system while drilling. A pump with two fluid cylinders, as shown in Figure 4-99, is called a duplex pump. A three-fluid-cylinder pump, as shown in Figure 4-100, is called a triplex pump. Duplex pumps are usually double action, and triplex pumps are usually single action. 

Mud pumps consist of a power input end and a fluid output end. The power input end, shown in Figure 4-101, transfers power from the driving engine (usually diesel or electric) to the pump crankshaft. The fluid end does the actual work of pumping the fluid. A cross-section of the fluid end is shown in Figure 4-102. 

The hydraulic horsepower produced by mud pumps depends mainly on the geometric and mechanical arrangement of the suction piping. If suction-charging centrifugal pumps (e.g., auxiliary pumps that help move the mud to the mud pump) are not used, the pump cylinders have to be filled by the hydrostatic head. 

Figure 4-99. Duplex slush (mud) pump. (Courtesy National Oilwell.)...

Figure 4-101. Power end of mud pump. (Courtesy LTV Energy Products Company.)...

Figure 4-102. Cross-section of fluid end of mud pump Courtesy /-He. Cjnt. iC Cfc ...

Approximate Input HP Required for Duplex Mud Pump Operation [15]... 

In air drilling operation, large compressors and usually a booster compressor are used to compress atmospheric air and supply the required volumetric flowrate to the standpipe in much the same way that mud pumps supply mud for drilling. The volumetric flowrate of compressed air needed (which is usually stated in SCFM of air) depends upon the drilling rate, the geometry of the borehole to be drilled and the geometry of the drill string to be used to drill the hole [64,65]. 

Loss of circulation is not a big problem Ability to handle very high volumes of formation water High mud pump pressure requirements High casing/air line costs If parasite tubing Is used Some specialized equipment... 

Start the mud pump, running as slowly as possible, to pump fluid at a rate of 1.5 to 2.0 bbl/min. This reduces fluid friction resistance pressures to a minimum and pumps at minimum standpipe pressure for circulation. The standpipe pressure (for 1.5 to 2.0 bbl/min) can be found from standard fluid hydraulic calculations. 

The development of positive displacement downhole motors began in the late 1950s. The initial development was the result of a United States patent filed by W. Clark in 1957. This downhole motor was based on the original work of a French engineer, Rene Monineau, and is classified as a helimotor. The motor is actuated by drilling mud pumped from the surface. There are two other types of positive displacement motors that have been used, or are at present in use today the vane motor and the reciprocating motor. However, by far the most widely used positive displacement motor is the helimotor [79,83]. 

Triplex Mud Pump, Model 10-P-13 National Supply Company, Example 2... 

Total Pressure Loss. Since bit life is not an issue in a short deviation control motor run operation, it is desirable to operate the positive displacement motor at as high a power level as possible during the run. The motor has a maximum pressure loss with which it can operate. This is 580 psi (see Table 4-114). It will be assumed that the motor will be operated at the 580 psi pressure loss in order to maximize the torque output of the motor. To obtain the highest horsepower for the motor, the highest circulation flowrate possible while operating within the constraints of the surface mud pump should be obtained. To obtain this highest possible, or optimal, circulation flowrate, the total pressure losses for the circulation system must be obtained for various circulation flowrates. These total pressure losses tabulated in the lower row of Table 4-117 represent the surface standpipe pressure when operating at the various circulation flowrates. 

Pump Limitations. Table 4-116 shows there are six possible liner sizes that can be used on the Model E-700 mud pump. Each liner size must be considered to obtain the optimum circulation flowrate and appropriate liner size. The maximum pressure available for each liner size will be reduced by a safety factor of 0.90. The maximum volumetric flowrate available for each liner size will also be reduced by a volumetric efficiency factor of 0.80 and an additional safety factor of 0.90. Thus, from Table 4-116, the allowable maximum pressures and allowable maximum volumetric flowrates will be those shown in Figures 4-207 through 4-212, which are the liner sizes 5j-, 6, 6-[, 6- and 7 in., respectively. Plotted on each of these figures are the total pressure losses for the various circulation flowrates considered. The horizontal straight line on each figure is... 

Signal pressure transducer (SPT) at mud pump records wave phase at stad. 

Wave frequency (/) is determined from mud pump strokes per minute. 

The mud pump performance characteristic can be thought of as being composed of two operating ranges. 

Range 1 of the mud pump performance characteristic is defined by the performance of the smallest liner, and range 2 is defined by the remaining liners. The pressure loss in a circulating system, except for bit (p ), can be estimated from numerous theoretical formulas or from a flowrate test. Data obtained from a flowrate test can be approximated using a curve-fitting technique by the following function ... 

Decrease in pump pressure. When less dense formation fluid enters the borehole, the hydrostatic head in the annulus is decreased thus, the pressure supplied by mud pumps is decreased. Although reduction in pump pressure... 

The volume capacity of the mud pump per stroke q (ft /stroke) (see section titled Mud Pumps ) is... 

Therefore, the mud pumps are used to fill the remainder of the casing string at a rate of 300 gal/min. Thus, the additional time T, to get the bottom plug to the float collar is... 

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