Page 57 - Primer on Enhanced Oil Recovery

48 Primer on Enhanced Oil Recovery

at the termination of washing to keep the drilled parts of the rock in suspension;
prevent the wall collapse and penetration of gas, oil and water from the drilled formations
into the well;
create a mudcake of the borehole wall;
cool the drill bit, the downhole motor and the drill string;
lubricate moving parts;
transfer energy to a turbo-drill;
protect drilling equipment and drill string from corrosion and abrasive wear;
be stable at elevated temperatures and inert to connate water and rock debris;
be convenient for cooking, pumping and cleaning;
allow prolonged cyclic use;
be safe for the service personnel and environment.

One can see that it is long list of requirements to satisfy.

6.3 Well completion

For effective development and operation of the well in the process of drilling pro-
ductive oil horizons, it is necessary to ensure the conditions of minimal disruption
of the natural reservoir properties of oil-bearing or gas-bearing strata. In this case,
productive formations after their drilling will be almost in the usual conditions and
will be able to give out the maximum possible amounts of hydrocarbons during
operation.
In the process of drilling wells to productive strata and putting the well into
operation (production), the sequence of work is performed. It is usually referred as
well completion. The well completion includes:

initial reservoir assessment;
selection of wellbore design;
choice of wellhead equipment;
provision for production string connection with the oil containing strata (secondary open-
ings to productive strata by perforation);
demonstration of oil flow at the ground level and well commissioning.
The well production, its operation profitability, the well production lifetime to
the great extend depend on the results of the above works.
Also very important is the well drilling termination scheme (lower completion),
which can be: an open hole, a filter with slit-like openings, an interval with parti-
tions packers for strata isolation, or a lowered and then perforated casing. The
choice of termination method can have a significant impact on the operation of the
well and, therefore, drilling, completion, production engineers and geologists should
evaluate various factors that influence the efficiency of the well operation.
Well classification can be carried out according to its intended purpose, accord-
ing to its profile, according to operational and economic criteria. The classification
is carried out in connection with the complex considerations of geological and