BAKER HUGHES - Drilling Fluids Reference Manual

RESERVOIR APPLICATION FLUIDS
selected. If a brush is used it should be redressed after each application. Non-rotating scrapers are
also available.
Circulating subs should be used to enable high circulating rates. There are two major different
types of circulating subs: ball drop type and weight-set sub.
The ball drop type is the most common used. The circulation ports are opened by dropping a
chrome-steel ball down the drill string, and then starting the mud pumps. With 1000 – 2000 psi
fluid pressure, the ball shears the pin holding the sleeve, the ball and sleeve then drop, opening the
ports and diverting the downhole flow. (See figure below)
Figure 6 - 21
Ball drop circulating sub
Once the flow has been diverted, it can not be re-diverted and the ability to circulate to the bottom
of the well is lost. This type of circ. sub allows rotation and reciprocation of the clean out string
while circulating. Circulating subs should be installed above mud-motor and at every casing size
increase, where Advantage Hydraulic simulations indicate that it will be necessary to achieve high
enough circulating rate. A multifunction ball opening circulating sub is available in the market, but
the failure rate has been high in some regions.
The weight-set circulating tool relies on maintaining weight set down on the tool to maintain the
circulation path, all circulation is at one point. These tools should be run with the clutch option
allowing drill pipe to be rotated independently of the pipe inside the liner. This tool can be actuated
as many times as required.
Junk catcher should be used if there is any concern about debris or junk in the well. Baker Oiltools
has a Junk catcher called ‘The Wellbore Custodian’. This is designed to seek out junk, collect it and
the carry it to surface. The fluid passing through is being filtered through stainless steel screen.
When RIH the tool will act as a boot basket allowing collection of large debris using fluid flow as it
passes through the tool. When pulling out of hole, the bypass is closed and the tool now diverts
fluid through the filter media capturing the debris.
Magnets should be used to remove ferrous steel debris and swarf (metal filings, shavings, etc.). The
downhole magnet is used to assist with cutting and milling debris removal where either low annular
velocity, or with well fluids that have poor carrying capacity, is used. Typical locations of the
magnets are just above the scrapers.
Conditioning the Mud System
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 6-90