Shale shakers Suction line

PREPAREDNESS
It is important to know the circulating volume and rate at which density can be increase with the rig’s mixing system.
KICK AND LOST CIRCULATION
If one of the formations exposed is weak and cannot withstand the wellbore pressures then lost circulation will occur, complicating the well killing procedure.
LOSSES ABOVE KICK
The problem is to provide a variable hydrostatic head whereby the exerted pressure at the kick zone is sufficient to kill the well and the pressure at the loss zone is insufficient to lose drilling fluid. A tricky situation.
In severe cases, trying to circulate different density fluids around will not be successful. The generally accepted method is to set a barytes plug over the overpressured zone. This will provide a very heavy and impermeable barrier. The losses can then be cured before drilling ahead
The plug is basically a slurry of barytes and water that is pumped down the drill pipe and placed at the bottom of the wellbore. The purpose of the barytes plug is twofold:

• 
  Kill the well
  
• 
  Settle and mechanically plug the wellbore.
  

The barytes plug is mixed and pumped on the fly; usually with a cement unit. Once started, pumping cannot stop until the plug is outside the drill string. Otherwise it will bridge off and stop any circulation capability.

LOSSES BELOW KICK
This is the more difficult situation of the two. The losses must be tackled first and then the well killed.
However the influx must be controlled from rising up the annulus. Weighted fluid must be continually pumped into the top of the annulus to stop ingress of the kick material. Low density drilling fluid must be continually pumped in through the drillpipe to satisfy the losses to the thief zone thus minimising the loss of weighted fluid.
When remedial action taken to combat the lost circulation, it must be mixed separately to the circulating fluid and then placed without stopping circulation to avoid losing control.
The major problem is being able to prepare all of the drilling fluids fast enough to maintain control.
11 Directional Drilling
In the early days of land drilling most wells were drilled vertically, straight down
into the reservoir. Although these wells were considered to be vertical, they rarely
were. Some deviation in a wellbore will always occur, due to formation effects and
bending of the drillstring. The first recorded instance of a well being deliberately
drilled along a deviated course was in California in 1930. This well was drilled to
exploit a reservoir which was beyond the shoreline underneath the Pacific Ocean.
It had been the practise to build jetties out into the ocean and build the drilling rig
on the jetty. However, this became prohibitively expensive and the technique of
drilling deviated wells was developed. Since then many new techniques and special
tools have been introduced to control the path of the wellbore.
An operating company usually hires a directional drilling service company to:
provide expertise in planning the well; supply special tools; and to provide onsite
assistance when operating the tools. The operator may also hire a surveying
company to measure the inclination and direction of the well as drilling proceeds.
In this chapter we will discuss: the applications of directional well drilling; the design
of these wells; and the techniques used to drill a well with controlled deviation from
the vertical. The next chapter will discuss the tools and techniques used to survey
the position of the well (determine the three dimensional position of all points in the
wellbore relative to the wellhead).
There are many reasons for drilling a non-vertical (deviated) well. Some typical
applications of directionally controlled drilling are shown in Figure 1.
(a) Multi-well Platform Drilling
Multi-well Platform drilling is widely employed in the North Sea. The development
of these fields is only economically feasible if it is possible to drill a large number of
wells (up to 40 or 60) from one location (platform). The deviated wells are designed
to intercept a reservoir over a wide aereal extent. Many oilfields (both onshore and
offshore) would not be economically feasible if not for this technique.
(b) Fault Drilling
If a well is drilled across a fault the casing can be damaged by fault slippage. The
potential for damaging the casing can be minimised by drilling parallel to a fault
and then changing the direction of the well to cross the fault into the target.
(c) Inaccessible Locations
Vertical access to a producing zone is often obstructed by some obstacle at surface
(e.g. river estuary, mountain range, city). In this case the well may be directionally
drilled into the target from a rig site some distance away from the point vertically
above the required point of entry into the reservoir.
(d) Sidetracking and Straightening
It is in fact quite difficult to control the angle of inclination of any well (vertical
or deviated) and it may be necessary to ‘correct’ the course of the well for many
reasons. For example, it may be necessary in the event of the drillpipe becoming
stuck in the hole to simply drill around the stuckpipe (or fish), or plug back the
well to drill to an alternative target.
(e) Salt Dome Drilling
Salt domes (called Diapirs) often form hydrocarbon traps in what were overlying
reservoir rocks. In this form of trap the reservoir is located directly beneath the
flank of the salt dome. To avoid potential drilling problems in the salt (e.g. severe
washouts, moving salt, high pressure blocks of dolomite) a directional well can be
used to drill alongside the Diapir (not vertically down through it) and then at an
angle below the salt to reach the reservoir.
(f) Relief Wells
If a blow-out occurs and the rig is damaged, or destroyed, it may be possible to
kill the “wild” well by drilling another directionally drilled well (relief well) to
intercept or pass to within a few feet of the bottom of the “wild” well. The “wild”
well is killed by circulating high density fluid down the relief well, into and up the
wild well.
12 Directional Surveying
When drilling a directional well, the actual trajectory of the well must be regularly
checked to ensure that it is in agreement with the planned trajectory (Figure 1). This is done by surveying the position of the well at regular intervals. These surveys will be taken at very close intervals (30’) in the critical sections (e.g. in the build-up section) of the well. Whilst drilling the long tangential section of the well, surveys may only be required every 120'. The surveying programme will generally be specified in the drilling programme. If it is found that the well is not being drilled along its planned course, a directional orientation tool must be run to bring the well back on course. In general the earlier such problems are recognised the easier they are to be corrected. Surveying therefore plays a vital role in directional drilling.