Page 134 - Drilling Technology in Nontechnical Language

Chapter 5 – RIG SELECTION AND RIG EQUIPMENT 125

At the start of the well, the requirement for output pressure is relatively

low (below 1,000 psi). At the same time, the pumps must give a high flow

rate; drilling the top hole section of perhaps 26″ will require flow rates in
excess of 1,200 gal/min. As the well is deepened, the pressure requirement
increases, but the volume requirement decreases. The pump cylinders and

pistons can be changed, so that for higher pressures and lower flow rates,

smaller cylinders and pistons can be fitted.

The power required for a given flow rate and pressure can be calculated.
The formula for hydraulic horsepower is:

Hydraulic horsepower (HHP) = PQ ÷ 1,714

where

P is the pressure in psi, and
Q is the flow rate in gallons per minute.

For a given hydraulic horsepower, pressure is inversely proportional to

flow rate; if the pressure doubles, the flow rate must halve for a given HHP.

This is fortunate because if a pump is capable of producing a certain HHP
at a certain pump speed, the maximum pump pressure can be increased
by fitting smaller cylinders and pistons. This also lowers the maximum

available flow rate.

The pump output flow is directed into a series of high-pressure

pipes leading to the drill floor. On the drill floor is a manifold (called the

standpipe manifold), which is a set of pipes and valves that allow the flow
to be directed to different places (fig. 5–13). Normally while drilling, the

standpipe manifold is set up to direct the flow down the drillstring. Also on
the standpipe manifold are positioned pressure gauges that allow the driller
to monitor the pump output pressure. This is very important to make sure
that drilling continues efficiently and safely.

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