Well Stimulation Techniques (Hydraulic Fracturing)
Well Stimulation Techniques (Hydraulic Fracturing)
Well Stimulation Techniques (Hydraulic Fracturing)
By
Amit Verma
Assistant Professor
Petroleum Engineering Dept.
UPES, Dehradun
Skin Reduction: Hydraulic Fracturing
In a way, the skin can be considered as the measure of the quality of a well. It
is reasonable to look at any type of stimulation as an operation reducing the
skin.
In the latter case, it is more correct to refer to the pseudoskin factor, indicating
that stimulation causes some changes in the streamline structure as well.
An important aspect of the skin factor is illustrated below. Reducing the skin from 1 to
zero has a bigger impact on the production of an ‘‘average’’ oil well than reducing it
from 25 to 20. In other words, the skin effect defines an intuitively ‘‘nonlinear’’ scale
to represent the quality of the well.
Proppants are used in hydraulic fracturing to prop or hold open the created
fracture after the hydraulic pressure used to generate the fracture has been
relieved.
The fracture filled with proppant creates a narrow but very conductive path
towards the wellbore.
In almost all cases, the overwhelming part of the production comes into the
wellbore through the fracture; therefore, the originally present near-wellbore
damage is ‘‘bypassed,’’ and the pretreatment positive skin does not affect the
performance of the fractured well.
Perhaps the best single variable to characterize the size of a
fracturing treatment is the amount of proppant placed into the
formation.
The fluid and additives act jointly to produce the hydraulic fracture when
pumped, transport the proppant into the fracture, then flow back to allow
the generated propped fracture to produce.
Stimulation costs for materials and pumping are estimated at 46% for
pumping, 25% for proppants, 19% for fracturing chemicals, and 10% for
acid.
Fluid use has evolved from exclusively oil-based in the 1950s to more than
90% crosslinked, water-based in the 1990s. Nitrogen and carbon dioxide
systems in water-based fluids are used in about 25% of all fracture stimulation
jobs.
Viscosity is one of the most important qualities associated with a fracturing
fluid. The most efficient viscosity-producing gum is guar, produced from the
guar plant.
The propping material has to be strong enough to bear the closure stress;
otherwise, the conductivity of the crushed proppant bed will be considerably
less than the design value (both the width and the permeability of the
proppant bed decrease).
Other factors considered in the selection process are size, shape, and
composition. There are two main categories of proppants: naturally occurring
sands and manmade ceramic and bauxite proppants.