Page 58 - Primer on Enhanced Oil Recovery

Introduction to well technology 49

economic factors. The classification adheres to the well-developed terminology for
oil and gas reserves.
The well classification used in the United States is an improved classification
which was proposed by F. Lahee in 1944. In accordance with the above classifica-
tion all wells are divided into two main categories: exploratory and field wells.
Exploration wells are subdivided into five groups and are linked to the produc-
tion and metering system for exploration during drilling.
The classification allows to assess the degree of economic risk in the production
of exploration and gives a deeper content of the classification of reserves discov-
ered at various stages of the exploration.

new-field wildcat is a well located on a structural or non-structural perspective trap,
within which no drilling operations were carried out or hydrocarbons have been produced.
As a rule, these wells are drilled in areas with unexplored or poorly studied local geologi-
cal conditions. Here the degree of risk taken by the entrepreneur in connection with the
desire to test an oil trap, the productivity of which has not yet been proved by drilling, is
high.
New-pool wildcat is a well drilled to explore a new reservoir on a structural or non-
structural trap outside the known boundaries of the productive area where oil or gas is
already being produced. In some areas where local geological conditions have been stud-
ied not so well, such exploration wells are sometimes referred to as “close wildcat”. The
distance of the location of such a well from the nearest productive area usually does not
exceed 3.2 km.
dipper pool (pay) test a well located within the boundaries of the productive area of a
reservoir or reservoir that is already partially or fully developed. The purpose of the well
is the exploration of the deep strata which lies below the reservoirs under development
shallower pool (pay) test a well being drilled in order to detect a new, not yet tested
reservoir, the presence of which according to previously drilled wells can be assumed in
the formations located above the developed or already developed reservoirs.
outpost or extension test wells are created for the purpose of prospecting a partially
developed reservoir, usually at a double (sometimes somewhat longer) distance compared
to the distance between production wells on the developed part of the reservoir.
In the contemporary well classification, according to the data of T. N. Murray (1988),
there can be three more groups of wells distinguished:
stratigraphic test a stratigraphic appraisal well is drilled to obtain specific geological
information that can detect oil or gas deposits. Such wells are intended only for core sam-
pling and (or) conducting any kind of well surveys. The wells are drilled without testing
for productivity.
service well an injection well is drilled in the field under development in order to
maintain reservoir pressure by pumping gas, water, air, steam, as well as for discharging
reservoir water, obtaining water for injection and as an observation well.
old well drilled deeper a well drilled below its previous bottom hole depth, which
may or may not lead to the discovery of industrial accumulations of hydrocarbons.
Field wells are production well which are drilled within an area of proven oil
and gas formation to the depth of the productive horizon. The category may include
not only the wells with which oil and gas is produced, but also wells for reserve
estimation, injection wells and observation wells.