Page 312 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 288

[ ] Well Programming
2.8.2

Costs

1. What are the costs of coring equipment and services, rig time,
transport and storage, lab analysis, mud treatments, etc.? How does
this compare to the budgeted cost?
2. How accurate can the cost estimates be? (May be affected by
knowledge of area, certainty of defined coring criteria, etc.)
3. What costs should be included in the drilling AFE (coring system
on the rig) and other AFEs (lab analysis)?
4. Who is responsible for tracking all the various cost elements?

Coring system considerations—choice of inner barrel. The length
of the core barrel and the type of formation will determine what kind
of inner tube to use. Those available include fiberglass (GRP) and alu-
minum disposable tubes, chrome lined steel tubes and GRP, aluminum,
sponge, and rubber sleeves that fit inside standard steel inner tubes.
A disposable tube is best for fractured or unconsolidated forma-
tions. The core and tube are recovered together and the tube is sewn
up with the core still inside. This protects the core and keeps it as
undisturbed as possible. GRP has a smooth ID, which reduces jamming
from fractured cores and is resistant to corrosive fluids. Aluminum
tubes are more robust than GRP tubes but are not as resistant to cor-
rosive attack. Both types can be run in core barrel assemblies up to 270
ft in length.
Liners can be used inside conventional steel inner tubes. Liners are
available in aluminum, plastic, and rubber. The main limitations to
using a liner are that a smaller diameter core is recovered and, in plas-
tic and rubber, temperature limitations apply.
Sponge coring (available from Diamant Boart Stratabit) uses an
aluminum tube with a sponge lining. This catches fluids expelled from
the core as it is pulled from the well. The core diameter will be less than
if a disposable or unlined steel tube were used.
Standard steel liners may be used where the formation is consoli-
dated and unfractured. The core is slid out of the liner on the catwalk,
sawed up, and boxed for transporting.
Coring system considerations—general type description. Some
typical coring systems and their applications are described below. The
descriptions are based on systems available from Eastman-Christensen.
Conventional core barrel. Suitable for most formations. Can be run

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