American Oil and Gas Reporter - August 2016 - 53

and 22.2 GPa, and shear modulus of 10.1
and 11.4 GPa. Poisson's ratio (0.28), density (2,620 kilograms/meter), cohesion
(7.5 GPa), friction angle (35 degrees)
and well diameters (16 centimeters) found
to be the same for both benches.
Vertical stress was calculated by integrating the density log from the surface
to the depth of the reservoir. Young's
modulus and Poisson's ratio were calculated through laboratory testing, comparing
lab data to the EERC geomechanical
data. Shear and bulk modulus was calculated from established relationships. Density data were obtained from laboratory
experiments as well as neutron-density
(CNL-FDC) logs from the field.
The first step was to make a 2-D
model of the horizontal section of the
well perpendicular to the wellbore, and
characterize the medium with assigning
elastic parameters to an undrilled formation. The calculated horizontal stress,
vertical stress and pore pressure were
assigned to the model correspondingly.
The program was executed to bring the
medium to its mechanical equilibrium.
The model was set to behave elastoplastically.
The second step was drilling the formation. In this step, a circular hole was
made through the model to configure the
drilled formation. To precisely evaluate
the results around the borehole, it was
decided to increase the number of grids
in this specific zone. The program was
then executed for the second round, and
a new mechanical equilibrium was
achieved. Deformations and displacements
in the formation took place during this
step.
Figures 2A and 2B show vertical and
horizontal displacement and stresses in
the upper Three Forks (first bench), while
Figures 3A and 3B show vertical and
horizontal displacement and stresses in
the middle Three Forks (second bench).
The simulation results indicate that
displacement in the first and second
benches does not vary significantly in either the vertical or horizontal directions.
The stresses in the horizontal direction
show almost the same pattern in both
layers, while the stress perturbation in
the vertical direction seems to be greater
in the lower layer. In addition, the results
show that the failure zones around the
borehole are minimal in both the lower
and middle Three Forks.
The depth differences and the properties
for both layers are very close, and therefore, do not considerably change the results. That said, since the wells are spaced
pretty far from one another, one would
not expect to see stress shadowing caused
by drilling. Wells in each layer are located

FIGURE 3A
Vertical (Left) and Horizontal (Right) Displacement in Middle Three Forks

FIGURE 3B
Horizontal (Left) and Vertical (Right) Stresses in Middle Three Forks

at a similar depth with the same layer
properties and with the same radii, so it
is logical they would have similar displacement, stress, and failure zones.
According to the stress and displacement contours, wells that are more than

10 meters apart should not impact one
another. The study's results suggest that
drilling high-density megapads or multilateral boreholes should not cause instability issues on the horizontal section in
the Three Forks formation.
r

AUGUST 2016 53

American Oil and Gas Reporter - August 2016

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