gas.rst

Gas PVT

Calculation Methods and Class Objects

pyResToolBox uses class objects to track calculation options through the functions. Class objects can be set via strings or explicitly via object options

Method Variables & Class Objects

Class Variable	Class Object	Class Description & Options
zmethod	z_method	Method for calculating gas Z-Factor. Defaults to 'DAK'. Options are: + 'DAK': Dranchuk & Abou-Kassem (1975) using from Equations 2.7-2.8 from 'Petroleum Reservoir Fluid Property Correlations' by W. McCain et al. - Slowest, Most Accurate + 'HY': Hall & Yarborough (1973) - Second Fastest + 'WYW': Wang, Ye & Wu (2021) - Fastest, Least Accurate
cmethod	c_method	Method for calculating gas critical properties. Defaults to 'PMC' Options are: + 'SUT': Sutton with Wichert & Aziz non-hydrocarbon corrections + 'PMC': Piper, McCain & Corredor (1999) correlation, using equations 2.4 - 2.6 from 'Petroleum Reservoir Fluid Property Correlations' by W. McCain et al.

Users can specify which calculation method to use either by passing an option string, or a class object to any given function. The implementation of class objects should make it easier to program in an IDE that supports type hinting

Examples:

Calculating bubble point pressure with Standing correlation via option string, and then via class object

>>> rtb.oil_pbub(api=43, degf=185, rsb=2350, sg_g =0.72, pbmethod ='STAN')
6406.067846808766

>>> rtb.oil_pbub(api=43, degf=185, rsb=2350, sg_g =0.72, pbmethod = rtb.pb_method.STAN)
6406.067846808766

Function List

Gas Functions

Task	Function
Gas Tc & Pc Calculation	pyrestoolbox.gas_tc_pc
Gas Z-Factor Calculation	pyrestoolbox.gas_z
Gas Viscosity	pyrestoolbox.gas_ug
Gas Viscosity * Z	pyrestoolbox.gas_ugz
Gas Compressibility	pyrestoolbox.gas_cg
Gas Formation Volume Factor	pyrestoolbox.gas_bg
Gas Density	pyrestoolbox.gas_den
Gas Water of Condensation	pyrestoolbox.gas_water_content
Convert P/Z to P	pyrestoolbox.gas_ponz2p
Convert Gas Gradient to SG	pyrestoolbox.gas_grad2sg
Delta Pseudopressure	pyrestoolbox.gas_dmp
Gas Condensate FWS SG	pyrestoolbox.gas_fws_sg

pyrestoolbox.gas_tc_pc

gas_tc_pc(sg, n2 = 0, co2 = 0, h2s = 0, cmethod = 'PMC', tc = 0, pc = 0) -> tuple

Returns a tuple of critical temperature (deg R) and critical pressure (psia) for hydrocarbon gas. If one or both of the tc and pc parameters are set to be non-zero, then this function will return that unchanged value for the corresponding critical parameter.

Inputs

Parameter	Type	Description
sg	float	Gas SG relative to air
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_tc_pc(sg=0.7, co2 = 0.15)
(363.9387708314338, 738.3190067714969)

>>> rtb.gas_tc_pc(sg=0.7, co2 = 0.15, tc=365, cmethod='SUT')
(365, 709.2389730048743)

pyrestoolbox.gas_z

gas_z(p, sg, degf, zmethod='DAK', cmethod='PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0) -> float or np.array

Returns gas Z-factor (either float or Numpy array depending upon type of p specified) using specified method. A float or list / array can be used for p, returning corresponding 1-D array of Z-Factors. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use precalculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas Z-factor. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_z(p=1000, sg=0.75, degf=160, n2 = 0.02, co2 = 0.17)
0.9140707840075585

>>> rtb.gas_z(p=1000, sg=0.75, degf=160, n2 = 0.02, co2 = 0.17, zmethod='HY')
0.9141985223206194

>>> rtb.gas_z(p=[1000, 2000], sg=0.75, degf=160, cmethod='SUT', n2 = 0.02, co2 = 0.17)
array([0.91920553, 0.87196032])

pyrestoolbox.gas_ug

gas_ug(p, sg, degf, zmethod ='DAK', cmethod = 'PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0) -> float or np.array

Returns gas viscosity (cP) using Lee, Gonzalez & Eakin (1966) correlation. A float or list / array can be used for p, returning corresponding 1-D array of gas viscosities. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use pre-calculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas Z-factor. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_ug(p=1000, sg=0.75, degf=180, zmethod ='HY', cmethod = 'SUT')
0.0141231843661131

>>> rtb.gas_ug(p=1000, sg=0.75, degf=180)
0.014114198868648963

pyrestoolbox.gas_ugz

gas_ugz(p, sg, degf, zee) -> float or np.array

Returns gas viscosity*Z-factor product (cP) using Lee, Gonzalez & Eakin (1966) correlation, utilizing a precaculated Z-factor A float or list / array can be used for p and zee, returning a 1-D array of gas viscosity*Z-factor products. Using the gas_ugz function instead of the product of the gas_ug and gas_z functions removes duplications in calculating the z-factor as well as the critical properties

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
zee	float, list or numpy array	Gas Z-factor(s)

Examples:

>>> rtb.gas_ugz(p=[1000,2000], sg=0.75, degf=140, zee=[0.9,1.0])
array([0.01219254, 0.01600964])

>>> rtb.gas_ugz(p=1000, sg=0.75, degf=140, zee=0.9)
0.012192537840814146

pyrestoolbox.gas_cg

gas_cg(p, sg, degf, n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0, cmethod ='PMC') -> float or np.array

Returns gas compressibility (1/psi) using the 'DAK' Dranchuk & Abou-Kassem (1975) Z-Factor & Critical property correlation values if tc and/or pc not explicitly specified A float or list / array can be used for p, returning corresponding 1-D array of gas compressibility's. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use precalculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_cg(p=2000, sg=0.68, degf=120, co2=0.05)
0.0005375634134905346

>>> rtb.gas_cg(p=np.array([1000,2000]), sg=0.68, degf=120, co2=0.05)
array([0.0011039 , 0.00053756])

pyrestoolbox.gas_bg

gas_bg(p, sg, degf, zmethod='DAK', cmethod = 'PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0) -> float or np.array

Returns gas formation volume factor (rcf/scf). A float or list / array can be used for p, returning corresponding 1-D array of gas FVF's. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use precalculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue.

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_bg (p=3000, sg=0.78, degf=240)
0.005930983977679231

>>> 1 / rtb.gas_bg (p=[3000, 5000], sg=0.78, degf=240)
array([168.60608691, 249.6801909 ])

pyrestoolbox.gas_den

gas_den(p, sg, degf, zmethod ='DAK', cmethod ='PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0) -> float or np.array

Returns gas density (lb/cuft) A float or list / array can be used for p, returning corresponding 1-D array of gas densities. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use precalculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue

Inputs

Parameter	Type	Description
p	float, list or np.array	Gas pressure (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_den (p=2000, sg=0.75, degf=150, zmethod ='HY', cmethod ='SUT', n2 = 0.02, co2 = 0.15, h2s = 0.02)
7.728991860473501

pyrestoolbox.gas_water_content

gas_water_content(p, degf) -> float

Returns saturated volume of water vapor in natural gas (stb/mmscf). From 'PVT and Phase Behaviour Of Petroleum Reservoir Fluids' by Ali Danesh.

Inputs

Parameter	Type	Description
p	float	Gas pressure (psia)
degf	float	Reservoir Temperature (deg F)

Examples:

>>> rtb.gas_water_content(p=1500, degf=165)
0.6521546577394491  

pyrestoolbox.gas_ponz2p

gas_ponz2p(poverz, sg, degf, zmethod='DAK', cmethod='PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0, rtol = 1E-7) -> float or np.array

Returns gas pressure corresponding to a value of P/Z, iteratively solving with specified zmethod via bisection. A float or list / array can be used for poverz, returning corresponding 1-D array of pressures. The cmethod will be used to calculate critical gas parameters unless tc and/or pc are explicitly set to be non-zero. This option enables users to use precalculate gas critical properties and so avoid repeated duplicated critical property calculations when compute time is an issue

Inputs

Parameter	Type	Description
poverz	float, list or np.array	Gas pressure / Z-factor (psia)
sg	float	Gas SG relative to air
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified
rtol	float	relative solution tolerance as compared with abs([User P/Z - Calculated P/Z] / [User P/Z])

Examples:

>>> rtb.gas_ponz2p(poverz=2500, sg=0.75, degf=165)
2082.5648307800293   

>>> rtb.gas_ponz2p(poverz=[2500,5000], sg=0.75, degf=165)
array([2082.56483078, 4890.62070847])

pyrestoolbox.gas_grad2sg

gas_grad2sg( grad, p, degf, zmethod='DAK', cmethod='PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0, rtol = 1E-7) -> float

Returns gas specific gravity consistent with observed gas gradient. Calculated through iterative solution method. Will fail if gas SG is below 0.55, or greater than 1.75

Inputs

Parameter	Type	Description
grad	float	Observed gas gradient (psi/ft)
p	float, list or np.array	Pressure at observation (psia)
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified
rtol	float	relative solution tolerance as compared with abs([User grad - Calculated grad] / [User grad])

Examples:

>>> rtb.gas_grad2sg(grad=0.0657, p=2500, degf=175)
0.7500786632299423   

pyrestoolbox.gas_dmp

gas_dmp(p1, p2, degf, sg, zmethod='DAK', cmethod = 'PMC', n2 = 0, co2 = 0, h2s = 0, tc = 0, pc = 0) -> float

Returns gas pseudo-pressure integral between two pressure points. Will return a positive value if p1 < p2, and a negative value if p1 > p2. Integrates the equation: m(p) = 2 * p / (ug * z)

Inputs

Parameter	Type	Description
p1	float, list or np.array	First gas pressure (psia)
p2	float, list or np.array	Second gas pressure (psia)
sg	float	Gas SG relative to air.
degf	float	Reservoir Temperature (deg F)
zmethod	string or z_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
cmethod	string or c_method	Method for calculating gas critical parameters. Calculation Methods and Class Objects.
n2	float	Molar fraction of Nitrogen. Defaults to zero if undefined
co2	float	Molar fraction of CO2. Defaults to zero if undefined
h2s	float	Molar fraction of H2S. Defaults to zero if undefined
tc	float	Critical gas temperature (deg R). Uses cmethod correlation if not specified
pc	float	Critical gas pressure (psia). Uses cmethod correlation if not specified

Examples:

>>> rtb.gas_dmp(p1=1000, p2=2000, degf=185, sg=0.78, zmethod='HY', cmethod = 'SUT', n2 = 0.05, co2 = 0.1, h2s = 0.02)
3690873383.43637  

>>> rtb.gas_dmp(p1=2000, p2=1000, degf=185, sg=0.78, tc = 371, pc = 682)
-3691052075.812854

pyrestoolbox.gas_fws_sg

gas_fws_sg(sg_g, cgr, api_st) -> float

Estimates specific gravity of full-wellstream (FWS) gas from gas-condensate well. Calculates from weighted average surface gas SG, CGR and API. Uses Standing correlation to estimate condensate MW from API. Returns SG of FWS gas

Inputs

Parameter	Type	Description
sg_g	float	Specific gravity of weighted average surface gas (relative to air)
cgr	float	Condensate gas ratio (stb/mmscf).
api_st	float	Density of stock tank liquid (API)

Examples:

>>> rtb.gas_fws_sg(sg_g=0.855, cgr=30, api_st=53)
0.9371015922844881