American Oil and Gas Reporter - January 2019 - 92

pages 87-93_Layout 1 1/9/2019 4:28 PM Page 92

FIGURE 4A

FIGURE 4B

Injection versus Pressure for S-10H Well

field. Second, all the defended wells were
located on the same pad. This meant they
all could be defended with one system
rig up. The next nearest well group was
located on a separate pad and would have
required a separate defense system.
Pressure transducers with the capability
of transmitting real-time data to remote
monitoring stations were installed on the
six legacy wells. Pumping equipment
was rigged up on the legacy wells allowing
for low-rate injection to occur in any or
all of the six wells. During stimulation
operations on the new wells, pressure interference with the legacy wells was evaluated based on the real-time data and
then injection was initiated when interference was detected. Pressure interference
between the four zipper wells also was
monitored via pressure transducers re-

porting to the frac van.
Five primary components are required
to implement this well defense strategy:
· A pump capable of pumping at
high pressure at relatively low rates. The
goal was to be able to pump into any
single well independently, or into any
combination of wells simultaneously, at
less than 2 bbl/minute per well. It was
hoped that low-rate injection would be
sufficient, especially considering the
higher cost of rigging up the horsepower
that would be required for higher rates.
· A manifold connecting the pump
to the wells, sufficient to either isolate or
combine injection into the defended wells.
· A water and chemical supply system
to feed the pump. Biocide and scale inhibitor were added to all injected water.
· Wellhead flowmeters and pressure

FIGURE 5
Combined Production from Six Legacy Wells

92 THE AMERICAN OIL & GAS REPORTER

Injection versus Pressure for S-11H Well

sensors to allow measurement of rates
and pressures at each well.
· A digital data system to allow both
the capture and real-time telemetry of
rate and pressure data on an individual
well basis.
The plan called for injection at the
soonest possible time following pressure
detection. However, this was difficult to
achieve in practice and there were often
delays. Nevertheless, the goal of injecting
against hits was carried out in most cases.
At the end of the project, 37,215 barrels
of freshwater treated with biocide and
scale inhibitor had been injected. That
included 10,509 barrels in S-11H, 2,678
in S-13H, and 7,453 in S-15H Middle
Bakken wells, and 11,025 barrels in S10H, 4.688 barrels in S-12H, and 862
barrels in S-14H Three Forks wells.
Frac Hits On Legacy Wells
During the course of the four-well
zipper frac, approximately 368 pressure
surges were detected in the legacy wells.
The character and timing of the pressure
events differed from well to well, although
there was a clear trend of decreasing
severity as the distance from the frac
wells increased. As might be expected,
the most severe surges were seen in the
S-10H, which is the legacy well nearest
to the frac pad, followed by the S-11H,
which is the next closest well.
Classifying frac hits as either minor
(less than 500 psi) or major (greater than
500 psi), S-10H has 91 total frac hits
(64 major), followed by S-11H with 89
frac hits (36 major). The net pressure increase in these two wells reached as high
as 1,570 psi. The S-12H, 13H, 14H and
15H wells experienced 19, 44, 44 and
81 hits, respectively, but none of them
were major.

American Oil and Gas Reporter - January 2019

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