Page 272 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 248

[ ] Well Programming
2.5.13

Aerated fluid drilling. This is simply injecting standard drilling
mud with air, effectively gas-cutting the returns and lightening the
fluid column. The main advantages are:

1. Maintaining full circulation in loss zones.
2. Increased ROP by reducing chip hold-down.
3. Reduced incidence of differential sticking.
4. Reduced formation damage.

Air may be injected at the standpipe or by other means, at an
appropriate rate in proportion to the mud circulation rate. Generally,
the technique is limited to a maximum depth of about 2800 ft, since
injection pressures become excessive at greater depths.

2.5.13. Tendering for Mud Services

Following are some points that might be considered. In many cases,
operating companies do not pay enough attention to tendering for the
mud services and suffer expensive wells as a result.
Lowest price is not always the lowest cost on the mud bill or the
total operating cost. Studies of many wells where a comparison
between mud companies performance can be made, can often show
that the lowest bidder can be the most expensive. This is not always
true in “high technology” areas, but is very common when working in
areas where not so much control can be exerted or is applied. Some
companies actively pursue a lowest price policy. The most alarming
case of how this can be detrimental would be in respect to oil muds. If
the lowest bidder’s oil mud causes substantial skin damage (compared
to others), it will not only have an effect on total operating cost but also
on field economics. It might necessitate costly remedial treatments. At
the worst, if wells do not flow because of damage, that damage
becomes 100% damage. The oil stays in the ground. This scenario is not
very common but it has happened on some occasions.
Direct mud service price may not be the only criteria for awarding
a contract; also evaluate technical support, valued added service, area
experience, and engineering quality criteria. When you award to a mud
company, you may wish to take on their area experience or additional

248