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various other maintenance works such as installation of gas lift
mandrels, new packing etc.
Through-tubing workover operations are work performed
with special tools that do not necessitate the time consuming full
workover procedure including replacement or removal of tubing.
Well maintenance without killing the well and performing full
workover is time saving and is often called well intervention.
Various operations that are performed by lowering instruments or
tools on a wire into the well are called wireline operations.
Work on the reservoir such as chemical injection, acid
treatment, heating etc is referred to as reservoir stimulation.
Stimulation serves to correct various forms of formation damage
and improve flow. Damage is a generic term for accumulation of
particles and fluids that block fractures and pores and limit
reservoir permeability.
 Acids, such as HCL (Hydrochloric Acid) are used
open up calcerous reservoirs and to treat accumulation of calcium
carbonates in the reservoir structure around the well. Several
hundred liters of acid (typically 15% solution in water) are
pumped into the well under pressure to increase permeability of
the formation. When the pressure is high enough to open fractures,
the process is called fracture acidizing. If the pressure is lower, it
is called matrix acidizing [14].
 Hydraulic fracturing is an operation in which a
specially blended liquid is pumped down a well and into a
formation under pressure high enough to cause the formation to
crack open, forming passages through which oil can flow into the
well bore. Sand grains, aluminum pellets, walnut shells, glass
beads, or similar materials (propping agents) are carried in
suspension by the fluid into the fractures. When the pressure is
released at the surface, the fractures partially close on the
proppants, leaving channels for oil to flow through to the well. The
fracture channels may be up to 100 meters, several hundred feet
long.
 Explosive fracturing, when explosives are used to
fracture a formation. At the moment of detonation, the explosion
furnishes a source of high-pressure gas to force fluid into the

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