American Oil and Gas Reporter - December 2021 - 64

SpecialReport: Stimulation & Completions
D-J Basin Field Trial
A field trial was executed on a fourwell
pad using a modified hydrochloric
acid replacement (HCR) system and ballin-place
plug to determine if operational
efficiencies could be achieved by spotting
the HCR with wireline and bottom-hole
assembly in the hole and perforating
through the HCR, instead of using traditional
spearhead methods and HCl. The
results show that the total pump time to
reach the designed frac rate and the total
stage pump time both decreased, while
the average pad rate per well increased.
These findings are significant in that
there was a noteworthy amount of time
and operational efficiencies observed by
spotting HCR with the wireline and BHA
in the hole.
Depending on the formation, pump
down rate, and wellbore volume, typical
pump down times for HCl can range between
10-20 minutes. This novel method
of spotting a HCR blend with wireline
essentially eliminates the time to displace
acid, saving an average of 6-20 minutes
per stage on a typical horizontal well in
the D-J Basin.
Using this approach to deploy acid
during wireline plug-and-perf operations,
FIGURE 1
DJ Basin Niobrara Formation
operators can achieve greater efficiency
and reduce cycle time and capital expense
while accelerating production due to faster
completion schedules.
The liquids-rich DJ Basin in Northeast
Colorado and Southeast Wyoming is composed
of various sandstone, chalk, marl,
and shale formations. The target in this
study focuses on the Niobrara formation,
which is composed of three separate
benches: the A, B and C (Figure 1).
The field trial consisted of utilizing a
ball-in-place plug and simultaneously
spotting HCR with the wireline and BHA
still in the hole. This method allows for
an operator to pump the tools down with
the spearhead acid to perforate the zone
in or near the acid, and let the acid sit
over the perforations or have the acid in
place next to the perforations. This approach
saves substantial time and water
in each stage of the well. This is followed
by removing the tool from the wellbore
and immediately initiating the fracture.
The HCR is essential to executing this
process since traditional HCl cannot be
pumped into the well with wireline equipment
because of its corrosive nature. The
HCR can be described as a " modified
acid " and is the product of a Lewis acid
base reaction, which leads to an " adduct "
or " complex. " It is formed by a Lewis
base, which is any species that has a
filled orbital containing an electron pair
that is not involved in bonding. Therefore,
it can act as an electron-pair donor. The
hydrogen ion acts as a Lewis acid, and
therefore, as an electron-pair acceptor.
This results in the formation of a dative
bond between the Lewis base and Lewis
acid to form a Lewis adduct.
As noted, one of the main operational
efficiency benefits of this approach is reduced
time to reach the designed frac
rate. A pumpdown unit was used to spot
HCR while pumping down the plug and
guns instead of waiting for wireline to
pull out of the hole, saving a significant
amount of water and time to complete
the stage. The HCR was delivered to location
as a concentrated material, and
then diluted using source water at a ratio
of one part HCR and two parts water.
Moving the acid pump down activities
off of the " critical path " of the frac crew
yields significant time savings, and results
in significant reductions in costs. Data
from the offset zipper frac well group, in
addition to a prior pad completed in the
same formation using traditional spearhead
HCl, was compared with the efficiencies
observed with the HCR versus HCl wells.
Well Results
6,200
Niobrara A
6,300
Niobrara B
6,400
Niobrara C
6,500
Codell
Greenhorn
6,600
Source: Bonanza Creek
64 THE AMERICAN OIL & GAS REPORTER
A four well pad was selected for this
portion of the trial (Pad A). Two wireline
crews were utilized to swap between
zipper groups on each pad (zipper group
A1 and A2). Comparing consecutive stages
on Well A1, Figures 2A and 2B show the
rate progression throughout the pumping
process. In total, 288 stages were completed
during this trial using HCR to initiate
formation breakdown.
Figure 2A shows Stage 53 in Well
A1, which utilized 15% HCl as traditional
spearhead acid. The shaded area in red
denotes the time associated with displacing
HCl from surface to reach the perfs. The
shaded area in blue denotes the time to
reach the designed rate once acid reached
the perfs (~31 minutes).
American Oil and Gas Reporter - December 2021

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