Page 26 - Petroleum and Gas Field Processing

concentrations of magnetite. Such information is utilized to identify the
presence of sedimentary formations above the basement rocks.
The seismic survey involves sending strong pressure (sound) waves
through the earth and receiving the reflected waves off the various surfaces
of the subsurface rock layers. The sound waves are generated either by
using huge land vibrators or using explosives. The very large amount of
data collected, which include the waves’ travel times and characteristics,
are analyzed to provide definitions of the subsurface geological structures
and to determine the locations of traps that are suitable for petroleum
accumulation.
This type of survey is the most important and most accurate of all of
the geophysical surveys. Significant technological developments in the field
of seismic surveying have been achieved in recent years. Improvements in
the data collection, manipulation, analysis, and interpretation have
increased the significance and accuracy of seismic surveying. Further, the
development of three-dimensional (3D) seismic surveying technology has
made it possible to provide 3D descriptions of the subsurface geologic
structures.
Remote sensing is a modern technique that involves using infrared,
heat-sensitive, color photography to detect the presence of underground
mineral deposits, water, faults, and other structural features. The sensing
device, normally on a satellite, feeds the signals into special computers that
produces maps of the subsurface structures.

1.4.3 Exploratory Drilling
The data collected from the geologic and geophysical surveys are used to
formulate probable definitions and realizations of the geologic structure
that may contain oil and/or gas. However, we still have to determine
whether petroleum exists in these geologic traps, and if it does exist, would
it be available in such a quantity that makes the development of the oil/
gas field economical? The only way to provide a definite answers is to drill
and test exploratory well(s).
The exploratory well, known as the wildcat well, is drilled in a
location determined by the geologists and geophysicists. The well is drilled
with insufficient data available about the nature of the various rock layers
that will be drilled or the fluids and pressures that may exist in the various
formations. Therefore, the well completion and the drilling program are
usually overdesigned to assure safety of the operation. This first well,
therefore, does not represent the optimum design and would probably cost
much more than the rest of the wells that will be drilled in the field.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.