1. Driving across South Texas at dusk, it does not take
long to spot a bright red glow as one looks across the
horizon. Flares dance above the oil fields as excess vapors
are burned off during production. This oxidation process
has been occurring since the start of the oil industry and
until recently was regarded as the nature of the business.
But due to ever-increasing federal and state environmen-
tal emission regulations for greenhouse gas, volatile
organic compounds, and hazardous air pollutants, this
may soon be a sign of the past.
Producers are looking to solutions such as oil storage
tank vapor recovery units (VRUs), vapor recovery towers
(VRTs), and low-pressure separator flash gas recovery
(FGR) applications to eliminate gas flaring.
Today’s VRU applications are just as unconventional as
the horizontal oil plays across the US. Steep oil produc-
tion decline rates, inconsistent vapor production rates,
and liquid fallout in the compression phase due to the
Btu-rich vapor all contribute to the success and profitabil-
ity of VRU applications. Each application needs to be
evaluated carefully to determine which
system of controls is best suited to meet
the specialized requirements of VRU and
FGR applications. In addition to the envi-
ronmental advantages that these regula-
tions provide, there is also an economic
silver lining through incentives that can
be recognized from recovered gas rev-
enue, recovered NGL, and the carbon
credit market.
The use of compression for vapor recov-
ery has been well proven; however, having
the correct controls and configurations to
make it the most effective can be challeng-
ing. In the past there was little flexibility
with varying vapor volumes, which can
often occur due to rapid decline rates or
early instability of production rates.
Compressco Partners has modified the controls of its
46-hp GasJack compressor design, which offers flexibility
from a compression ratio standpoint in addition to the
large suction/discharge operating parameters that can
be achieved. Through its experience in unconventional
oil plays, the company has developed systems that can
achieve up to 98% control efficiency. Sharp vapor pro-
duction declines and fluctuations can wreak havoc on
VRU systems if the proper criteria are not met. The com-
pressor applies makeup and recycled gas systems, speed,
capacity control methods, and automatic start/stop to
optimize the machine to the individual production at
each location. Unlike other types of VRU compressors,
the GasJack has the ability to handle wet gas streams
(greater than 2.5 BBtu) with minimal efficiency losses
due to contamination from liquid fallout.
For applications where an electric solution is preferred
to capture vapors, there are several options with varying
ranges in the company’s V-Jack line of compressors. All
of the compressors can be used on the various types of
VRU applications.
The industry has seen an increase in the vapor recovery
market from 64% in areas such as the Niobrara/Bakken
to more than 175% in the Eagle Ford during 2012. Flash
February 2013 | EPmag.com90
Economical solutions meet state and
federal mandates for gas flaring
Vapor recovery unit offers economic and environmentally friendly solutions
for enhanced production using recovered gas vapor.
Sheri Vanhooser and Steve Torrez,
Compressco Partners LLP
WELLHEAD PAD
DESIGN/EQUIPMENT
The multistage FGR system eliminates
the need for flaring. (Images courtesy
of Compressco Partners LLP)
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2. February 2013 | EPmag.com92
WELLHEAD PAD
DESIGN/EQUIPMENT
separator applications in the Appalachian regions
increased approximately 30% in 4Q 2012. Regulations
requiring capture of vapors during flowback will also dra-
matically increase the need for VRUs on new drills.
Direct from storage tanks
The traditional method for recovering tank vapors is
pulling the vapors directly off a common vent header
across the top of all the oil storage tanks to capture losses.
This method works very well with large-capacity storage
tanks where the vapor production rate is fairly constant,
such as central gathering facilities. However, an individual
or small-cluster well pad presents challenges to compres-
sor optimization due to standard daily operating proce-
dures such as tank gauging and oil loading. Compressco
assisted an operator in southeast Texas with its VRU appli-
cation needs, providing recommendations for addressing
oxygen ingress. A Fisher gas padding system was installed,
thief-hatch spring weight and seal material were changed,
and an O2 sensor was installed on the discharge side of
the compressor. The makeup system is controlled with a
pilot controller operating in inches of water column. The
automatic start/stop compressor was configured to 50%
volume capacity, and the speed was set at 75% of rated
maximum allowable. The well produced 350 b/d to 400
b/d of 48˚API gravity oil, and the VRU sales meter aver-
aged 70 Mcf/d in July 2011 and is still in operation. This
setup reduced the risk of oxygen ingress and was econom-
ically viable. Most importantly, the operator was in com-
pliance with regulations.
Vapor recovery towers
A VRT is a vessel designed as a final stage of gas separa-
tion between the heater treater, production unit, or low-
pressure separator and the storage tanks and is operated
near atmospheric pressure. VRTs provide a liquid barrier
between the VRU compressor and the oil storage tanks,
eliminating the potential for oxygen ingress from the
storage tank battery. By reducing the pressure drop
between the production equipment and the oil storage
tanks, the VRT reduces the flashing losses that occur in
the storage tanks to levels below state and federal emis-
sion requirements.
Several large operators in the Eagle Ford shale have
chosen the VRT as the primary method for capturing
vapor emission. With more than 100 GasJack compressors
in this play, its success is due to a proven track record on
handling high-Btu vapor, compressor operating flexibility,
service capabilities, and equipment availability. Due to the
steep production decline rates in the Eagle Ford, the
company has had many locations where multiple units
were set upon startup. As the production declined, the
unit count was reduced by moving these units to new
locations coming online.
Flash gas recovery
Flash gas in the oil field refers to the gas released by the
pressure and temperature drops during the extraction
and separation process at the well site. The flash process
often occurs when pressures are below the pressure
required for the gas to be discharged to the sales or
gathering pipeline. This gas was often sent to a flare
on location and destroyed. As fields mature, midstream
companies lower the pipeline pressures to allow for the
free flow of natural gas into the compressor stations or
processing plants. The current revitalization of old fields
is due to unconventional drilling technology and opera-
tors capitalizing on the opportunity to capture the previ-
ously flared gas using low-cost compression.
Recently, an operator in Ellis County, Okla., produced a
well making an average of 300 b/d of oil and immediately
noticed the increased flaring from the low-pressure sepa-
rator. When the GasJack unit was delivered and installed
at the location, the line pressure was 225 psig. The com-
pressor was set up to pull the low-pressure separator to 7
psig and discharge to 225 psig. The first full day of FGR
production totaled 153 Mcf/d, and the company held
that average for several months for a return on invest-
ment of 6.5:1 at a gas price of US $3.
Vapor recovery units will help operators be in full compliance
with EPA regulations set for 2015 that will no longer allow gas
flaring.
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