Lecture 1 con't

1.1.3 Applications of Directional Drilling
1. Sidetracking: Side-tracking was the original directional drilling technique. Initially,
sidetracks were “blind". The objective was simply to get past a fish. Oriented
sidetracks are most common. They are performed when, for example, there are
unexpected changes in geological configuration (Figure 1-1).


2. Inaccessible Locations: Targets located beneath a city, a river or in environmentally
sensitive areas make it necessary to locate the drilling rig some distance away. A
directional well is drilled to reach the target (Figure 1-2).



3. Salt Dome Drilling: Salt domes have been found to be natural traps of oil
accumulating in strata beneath the overhanging hard cap. There are severe drilling
problems associated with drilling a well through salt formations. These can be
somewhat alleviated by using a salt-saturated mud. Another solution is to drill a
directional well to reach the reservoir (Figure 1-3), thus avoiding the problem of
drilling through the salt.



4. Fault Controlling: Crooked holes are common when drilling nominally vertical. This
is often due to faulted sub-surface formations. It is often easier to drill a directional
well into such formations without crossing the fault lines (Figure 1-4).



5. Multiple Exploration Wells from a Single Well-bore: A single well bore can be
plugged back at a certain depth and deviated to make a new well. A single well bore
is sometimes used as a point of departure to drill others (Figure 1-5). It allows
exploration of structural locations without drilling other complete wells.



6. Onshore Drilling: Reservoirs located below large bodies of water which are within
drilling reach of land are being tapped by locating the wellheads on land and drilling
directionally underneath the water (Figure 1-6). This saves money-land rigs are much
cheaper



7. Offshore Multiwell Drilling: Directional drilling from a multiwell offshore platform
is the most economic way to develop offshore oil fields (Figure 1-7). Onshore, a
similar method is used where there are space restrictions e.g. jungle, swamp. Here,
the rig is skidded on a pad and the wells are drilled in “clusters".



8. Multiple Sands from a Single Well-bore: In this application, a well is drilled
directionally to intersect several inclined oil reservoirs (Figure 1-8). This allows
completion of the well using a multiple completion system. The well may have to
enter the targets at a specific angle to ensure maximum penetration of the reservoirs.



9. Relief Well: The objective of a directional relief well is to intercept the bore hole of a
well which is blowing and allow it to be “killed" (Figure 1-9). The bore hole causing
the problem is the size of the target. To locate and intercept the blowing well at a
certain depth, a carefully planned directional well must be drilled with great
precision.



10. Horizontal Wells: Reduced production in a field may be due to many factors,
including gas and water coning or formations with good but vertical permeability.
Engineers can then plan and drill a horizontal drainhole. It is a special type of
directional well (Figure 1-10). Horizontal wells are divided into long, medium and
short-radius designs, based on the buildup rates used. Other applications of
directional drilling are in developing geothermal fields and in mining.