American Oil and Gas Reporter - May 2015 - 89

SpecialReport: Gas Compression Technology
to centralized production facilities; pads
with production separators and a single
multiphase flowline for oil, water and gas;
and various combinations of bulk and test
production separators.
For engineers tasked with designing
production facilities for high-volume horizontal well pads, selectively using PVT
data, coupled with modern process simulation tools and a solid understanding of
well operational requirements, can lead to
tighter and more economical designs.
Facilities costs typically represent 1025 percent of overall development costs,
but any reductions in capital and operating costs will help improve well economics and increase ultimate recovery. Lower commodity prices make it more important than ever to use the most appropriate
data and best-available technologies to optimize facilities and maximize recovery.
Simulations Using PVT Data

Reservoir and production engineers frequently run full PVT analyses to use in
planning field development strategies. A

PVT analysis is based on sampling an oil
well early in its life, analyzing the samples,
and measuring and projecting a number of
fluid properties important to completion
design and production operations. However, PVT data can also be used for numerical modeling to optimize facility design
and minimize the risk of either undersizing or oversizing a facility for a given application.
PVT samples are taken at the surface
separator, since it is difficult and expensive to get a representative sample of the
actual reservoir fluid from the bottom of
the wellbore. The samples are recombined
in the lab to be representative of the
reservoir fluid, using flow data to obtain
the gas-to-oil ratios. The original and recombined samples are analyzed by gas
chromatographs, resulting in carbon number (CN) analyses that typically include
nitrogen, carbon dioxide, hydrogen sulfide,
and hydrocarbons with CNs ranging from
C1 (methane) to components as heavy as
C24, C30, C36, and even higher for heavier crude oils.

In facility engineering design, PVT
analyses can be used to predict gas handling requirements for a pad or field, with
the reservoir fluid run in a process simulator to predict gas volumes and various
flash temperatures and pressures. The typical PVT analysis only provides CN totals and does not break down percentages
of paraffins, isoparaffins, olefins, naphthenes or aromatics (PIONA). While
reservoir engineers can request a PVT
analysis that includes the full range of carbon chains/aromatics, it is more expensive and not a common practice. This has
left facility engineers with the option either to make gross guesses about the
breakdown of these components, or to use
simple straight-chain paraffins in simulations.
Some process simulation software developers have taken up the challenge by
developing calculation techniques that
mimic the effects of the various hydrocarbon species. We have performed a study
using one such technique developed by the
Virtual Materials Group for its VMG

TABLE 1
Process Simulation Comparison
Alkane Simulation

PIONA Simulation

HPS

LPS

Recovered
Tank Flash

Temperature, °F

90.0

120.0

117.0

90.0

120.0

117.0

Pressure, psia

112.0

27.0

12.0

112.0

27.0

12.0

OIL DATA

HPS

LPS

Recovered
Tank Flash

Oil Production

Oil Production

Oil Make, bbl/d, @ T,P

617.7

477.0

467.8

601.5

461.6

452.6

Oil Make, bbl/d, @ STD

609.1

463.1

454.8

596.3

451.3

443.0

Oil Density @ T,P

48.64

45.35

45.64

52.52

47.05

47.36

Oil Density @ STD

49.33

46.71

46.94

52.98

48.12

48.39

API Grav @ STD

47.39

57.40

56.47

35.06

51.86

50.86

RPV (ASTM D-323)

29.70

11.68

7.04

29.11

11.76

7.09

GAS DATA
Flow, Mcf/d
Separator Gas SG
Heating value, Btu/cf
MMBtu
Total Heating value, Btu/cf

Gas Production

Gas Production

512

36.1

11.6

517

34.3

11.6

0.812

1.356

1.777

0.814

1.369

1.756

1,350.0

2,125.0

2,853.0

1,352.4

2,161.6

2,866.4

76.7

33.1

699.2

74.1

33.3

691.2

1,431.1

1,432.9

Total MMBtu/d

801.0

806.6

Dew point @ 100°F

106.5

105.8

1,230.7

1,270.7

Well Gas-to-Oil Ratio

MAY 2015 89
American Oil and Gas Reporter - May 2015

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