Hydraulic fracturing has been used in the oil and
natural gas industry for the last 75+ years, booming for the last 10+ years,
producing hundreds of trillion cubic feet of natural gas and billions barrels
of oil using horizontal wells completions and multistage hydraulic fracturing,
producing from mili-darcy to micro-darcy to even
For any reservoir, Darcy law gives a quick
estimation of the productivity (Qi) of a reservoir from a well angle
by determining the flow through a permeable media, considering a 1-D,
homogeneous reservoir with single phase of fluid having constant fluid
viscosity. If we calculate the P.I. (Productivity index) using Darcy law and
constant flowing bottom hole pressure (Pf), for these tight and
shale reservoirs, most of the reservoirs below a mili-darcy, with no natural
fractures existing in-situ, will not qualify for economic development. Even,
few would not even produce anything without the help of artificial lift.Now
imagine, If there were no hydraulic fracturing technology, those reservoirs
would have been holding the enormous amount of hydrocarbons without
contributing to the world’s energy requirements.Below curves show how the well
production rates and cumulative production changes with hydraulic fracturing
Another graph from EIA shows the mammoth impact
of hydraulic fracturing on hydrocarbon production.
hydraulic fracturing and how does that help in higher production rates?
fracturing occurs when the injection pressure is increased above the rock
parting pressure.It does not change the permeability of the given formation. It
creates permeable channels for the reservoir fluids to flow-in from matrix to
wellbore, hence aiding for improved effective permeability through fractures permeability.
are two stages in a Frac job, Pad stage and Slurry stage. In Pad stage, only
fluid is injected to breakdown the formation. If there is no support to keep
the formation open, the fractures will close as soon as the pressure is
released, so in slurry stage, fracturing fluid is mixed with proppant and then
pumped in the formation above the rock parting pressure. This keeps the
formation open even after the pressure is released since proppant acts like
are mainly two types of hydraulic fracturing jobs, e.g. slick-water fracturing
and cross-linked fracturing with various gelling agents, friction reducers,
cross-linked adjusters, breakers, scale inhibitors, corrosion inhibitors,
oxygen scavengers, etc. to aid in efficient hydraulic fracturing job.
are different types of proppant with varied strengths and pressure ratings (100
mesh, 20/40, 30/50, ceramic etc.).
are three orthogonal, compressive and non-homogeneous stresses within the
formation. The principal stress direction is very important as it controls the
fracturing geometry, extension and direction of the fracture.
geometry includes Frac width, length and height. This is also known as S.R.V
(Stimulated Rock Volume). The bigger is the SRV, the higher initial rates are
expected in a similar formation. Fracturing height is generally independent of
fracture length and is governed by stress contract in vertical plane.
of the fractured wells is dependent on fluid flow from matrix to fracture and
from fracture to wellbore. Fluid flow from matrix to fracture is governed by
fracture geometry whereas from fracture to wellbore is governed by fracture
permeability. This improvement in productivity is classified as F.O.I (Fold of
increase) and the below curve represents the fold of increase with dimensional
less fracture conductivity.
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