Page 59 - Drilling Technology in Nontechnical Language

50 Drilling Technology in Nontechnical Language Second Edition

Casing design

Each casing string is completely specified, including the outside
diameter of the pipe, how thick it is, what sort of threads are needed to
screw the casing together, what type of steel will be used to make the
casing, and other information. Tools might be screwed into the casing
string at particular depths, and this must be specified so that the drilling

supervisor knows what to put where.

Geological information

In a wildcat exploration well, this information might be scarce or
nonexistent. In any case, there will always be some intelligent guesswork
involved, especially when the geologists try to estimate the strengths of the
rocks (formation fracture gradient) and pore pressure. These two pieces
of information are very important to drilling engineers because these are
what fundamentally dictate the casing program.
The formation lithologies, permeability, porosity, composition of pore

fluids, depths and thicknesses, and the stresses present in the rock are all
valuable information.

Logging program

Tools can be run into the well on special electrical cable to measure
various formation parameters. These are called electric logs. There
are several classes of electric logging tools that can be used to identify
important formation characteristics and to identify the fluids present in the

pore spaces.
Many different formation characteristics can be measured. By
combining several measurements, a comprehensive picture of any formation
can be built up, identifying physical and chemical characteristics.

_Devereux_Book.indb 50 1/16/12 2:06 PM