American Oil and Gas Reporter - August 2019 - 55

SpecialReport: Production Automation

Solutions Optimize Vapor Management
By Ray McKaskle
and Kevin Fisher
In onshore resource plays, the sheer
quantity of oil and gas production sites-
which can number in the hundreds or
even thousands for a single operator in a
large field-is a key factor in developing a
successful vapor control program. Many
sites lack access to electrical power and
other utilities, and control equipment is
often required to operate with only produced gas for a fuel source and a driver
for pneumatic devices. Sites typically are
unattended and only visited by production
personnel for a few minutes once or twice
a day. Management of water and hydrocarbon condensation, solids formation,
and related cold climate impacts also must
be addressed in a vapor control program.
All of these factors drive the need for
a low-cost, reliable and simple approach
to reducing the formation of vapors and
the emissions they generate. Vapor control
equipment often consists of a compressor-based vapor recovery unit (VRU) or
an open or enclosed flare (thermal oxidizer), or both.
There are several types of VRU compressors that can be used in production
site applications-including reciprocating,
rotary screw, rotary sliding vane and
scroll compressors-but they all are generally smaller in size and lower in cost
with higher suction pressures. Higher
suction pressure results in a lower actual
volumetric gas flow rate to be processed
and a lower compression ratio for the
same discharge pressure. Smaller equipment results in more revenue generation
per unit cost of control equipment and
reduces the size of additional control
equipment. Figure 1 shows a two-stage
reciprocating compressor VRU system
that one producer has used in more than
100 installations in one field.
As one might expect, there is no "onesize-fits-all" solution, but operators can
benefit from lessons learned in the field
over the past decade to identify and develop optimal VOC control solutions tailored to site-specific requirements.
Vapor Source Review
Wells can have continuous, free-flow
production or cyclic on/off operations.
They can be pumped via surface or downhole pumps or supported by gas lift, while

others rely on reservoir pressure and are
turned on/off by actuated valves on automatic timers. Some wells (particularly
older vertical wells) use plunger lift in the
production tubing to sweep accumulated
fluids to the surface. Several of these production operations result in discreet surges
in fluid production that can generate high
peak flow rates of vapor that must then be
controlled. In fact, we have observed peak
flash gas rates up to 30 times the daily average values.

Figure 2 shows a typical flow schematic
for a production separator ("heater
treater"). The production tubing transfers
the production stream from the wellhead
to a flowline that often flows through the
heated part of the production separator
before passing through an orifice (choke).
Heating helps to manage the temperature
drop as the pressure of the fluids is
reduced across the choke.
The three-phase mixture of oil, gas and
water is flashed into the separator. Sales

FIGURE 1
Two-Stage Reciprocating Compressor VRU

FIGURE 2
Single-Stage Production Separator
Fuel for Separator Burner,
Separator Pilot and
Flare Pilot
Sales Gas

Main
Separator
Burner

Three-Phase Separator

Oil to Storage Tank
Firetube

Feed Stream
From Well

Water

AUGUST 2019 55

American Oil and Gas Reporter - August 2019

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