Page 27 - Petroleum and Gas Field Processing

As this exploratory well is drilled, samples of the rock cuttings are
collected and examined for their composition and fluid content. The data
are used to identify the type of formation versus depth and to check on the
presence of hydrocarbon materials within the rock. Cores of the
formations are also obtained, preserved, and sent to specialized
laboratories for analysis. Whenever a petroleum-bearing formation is
drilled, the well is tested while placed on controlled production. After the
well has been drilled, and sometimes at various intervals during drilling,
various logs are taken. There are several logging tools, or techniques,
(electric logs, radioactivity logs, and acoustic logs) that are used to gather
information about the drilled formations. These tools are lowered into the
well on a wireline (electric cable) and, as they are lowered, the measured
signals are transmitted to the surface and recorded on computers. The
signals collected are interpreted and produced in the form of rock and
fluid properties versus depth.
The exploratory well will provide important data on rock and fluid
properties, type and saturation of fluids, initial reservoir pressure, reservoir
productivity, and so forth. These are essential and important data and
information, which are needed for the development of the field. In most
situations, however, the data provided by the exploratory well will not be
sufficient. Additional wells may need to be drilled to provide a better
definition of the size and characteristics of the new reservoir. Of course,
not every exploratory well will result in a discovery. Exploratory wells may
result in hitting dry holes or they may prove the reservoir to be an
uneconomical development.

1.5 DEVELOPMENT OF OIL AND GAS FIELDS

The very large volume of information and data collected from the various
geologic and geophysical surveys and the exploratory wells are used to
construct various types of map. Contour maps are lines drawn at regular
intervals of depth to show the geologic structure relative to reference points
called the correlation markers. Isopach maps illustrate the variations in
thickness between the correlation markers. Other important maps such as
porosity maps, permeability maps, and maps showing variations in rock
characteristics and structural arrangements are also produced. With all data
and formation maps available, conceptual models describing the details of the
structure and the location of the oil and gas within the structure are prepared.
The data available at this stage will be sufficient to estimate the
petroleum reserves and decide and plan for the development of the field
for commercial operation.

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