Page 73 - Hydrocarbon Exploration and Production Second Edition

60 Site Preparation

preventer has a rubber sealing element that is hydraulically inflated to fit tightly
around any size of pipe in the hole. Ram type preventers either grip the pipe with
rubber-lined steel pipe rams, block the hole with blind rams when no pipe is in
place or cut the pipe with powerful hydraulic shear rams to seal off the hole.
BOPs are opened and closed by hydraulic fluid stored under a pressure of
3000 psi in an accumulator, often referred to as a ‘Koomy’ unit.
All drilling activity will be carried out by the drill crew which usually works in
8- or 12-hour shifts. The driller and assistant driller will man the drilling controls on
the rig floor from where instrumentation will enable them to monitor and control
the drilling parameters, specifically

hookload
torque in drill string
weight on bit (WOB)
rotary speed (rpm)
pump pressure and rate
ROP (in min/ft)
mud weight in and out of the hole
volume of mud in the tanks.
Drilling operations which employ a measurement while drilling (MWD) system
(see Section 4.5) will also provide the drilling engineers with formation parameters,
downhole pressure and directional data in real time.
In addition to the drilling crews, drilling operations require a number of
specialists for mud engineering, logging, fishing, etc., not to forget maintenance
crews, cooks and cleaning staff. It is common to have some 40–90 people on site,
depending on the type of rig and the location. The operation is managed on site by
a ‘Company Man’ who represents the operator and a ‘Rig Manager’ who is the
drilling contractor’s representative.

4.4. Site Preparation

Once the objectives of the well are clear, further decisions have to be made.
One decision will be where to site the drilling location relative to the subsurface
target and which type of rig to use.
If no prior drilling activities have been recently carried out in the area, an
environmental impact assessment (EIA) will usually be carried out as a first step. An EIA
is usually undertaken to
meet the legal requirements of the host country
ensure that the drilling activity is acceptable to the local environment
quantify risks and possible liabilities in case of accidents.
An EIA may have to include concerns such as

protection of sites of special interest (e.g. nature reserves, archaeological sites)
noise control in built-up areas