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Click here to download the Meyer 2009
User’s Guide, including more information about Multiple
Fractures
Multiple fractures refers to the condition when more than one fracture
is created in the same zone. This is not the same as multilayer or limited
entry fracturing which initiate fractures in different zones. Consequently,
multiple zones can create multilayer fractures with each having their own
system of multiple fractures. Also, multiple fractures may or may not be
parallel to one another.
A definition of multiple fractures as implemented in MFrac is necessary
because of the general misconception of what they are and how they are
modeled. Multiple fractures can occur in two regions, the near wellbore and
far field. Each has a unique impact on the fracture geometry and pressure
response.
Near wellbore multiple parallel fractures occur near the wellbore. They
have been referred to as tortuosity (or a result of tortuosity), multiple
fractures, initiation fractures non-perpendicular to the minimum horizontal
stress, etc. Many times the cause of “excess Net Pressure” is postulated to
be multiple fractures.
Whether near wellbore pressure loss is a result of perforations,
tortuosity, multiple fractures, fracture initiation or some other form of
viscous dissipation, it can be modeled as a near wellbore pressure loss
function. This near wellbore pressure loss has been modeled by some using
the “Multiple Parallel Fracture” approach. In MFrac, near wellbore pressure
losses are entered into a table as a function of time and rate, since they
are not known a priori.
Only the far field multiple fractures are modeled as a fracture system
in MFrac. These fractures may propagate parallel to one another or spread
out in a dendritic (tree like or radial) pattern from the wellbore. These
multiple far field fractures may or may not interact.
Although, MFrac provides a number of options for modeling multiple
fractures, we do not believe they should be used as a general methodology
for increasing net pressure. These options should be used with care based
on sound engineering judgment.
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