Oil & Gas Apps

Easy to use engineering apps for the oil and gas industry - designed for practical field applications.
Apps have been tested and proven both on offshore and onshore oil and gas installations.

Designed for iPhone or iPad - available from the AppStore.
 

Gas-Leak calculates leak-rates from oil and gas leaks in oil and gas operations and equipment.

AGA-3 calculates size, flowrate or pressure drop for gas and liquid flow orifice meters based on the American Gas Association AGA report No. 3 (also API Manual of Petroleum Measurement Standards, Chapter 14.3).

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AGA-3 Orifice calculations are based on the American Gas Association AGA report No. 3 (also API Manual of Petroleum Measurement Standards, Chapter 14.3). Orifice size is calculated from given flowrate and pressure drop, Flowrate is calculated from given size and pressure drop and Pressure Drop requires orifice size and flowrate. Different taps can be selected: Flange taps or Pipe taps. Fluids include gases: Natural Gas (Specific Gravity must be provided), Air and Nitrogen, or liquids: Crude Oil, Water, Methanol, Mono-ethylene Glycol, Diethylene Glycol and Triethylene Glycol. In addition, selecting orifice material will adjust the sizing parameter of the orifice depending on temperature.

Physical Properties
Standard conditions for AGA-3 Orifice are defined according to US Customary system as 60 °F (15.56 °C) and 14.73 Psia (1.0156 Bara). Customary units (US) (Temp = °F, Pressure = Psia) and SI-units (Temp = °C, Pressure = Bara) are supported.

For natural gas the AGA-8 equation-of-state (EOS) is used for calculating Z-factor (compressibility factor) specific heat capacity and isentropic coefficient. For air and nitrogen, the Redlich-Kwong EOS is used. Other physical properties are calculated from common empirical equations used in the oil and gas industry (viscosity, pseudo-critical properties).

For liquids, the physical properties are calculated from common empirical equations used in the oil industry.

Orifice Meters with Flange Taps:

The fundamental orifice meter flow equation is:

Q_m =359.072C_d(FT)E_vY₁d²𝜌₁DP

where

Qm        = mass flow rate (lbm/hr)

359.072 = Conversion factor for flowrate in lbm/hr, d in inches, and DP in inches H2O

Cd(FT)  = coefficient of discharge for flange tapped orifice meters

Ev          = velocity of approach factor

Y1         = expansion factor (upstream tap)

d            = orifice plate bore diameter, inches

𝜌₁          = density of fluid at upstream flowing conditions, lbm/ft3 

DP         = orifice differential pressure, inches H2O at 60 °F

Cd(FT) = Ci(FT) + 0.000511 × (1,000,000 × ß/ReD)^0.7 + {0.0210 + 0.0049 × (19,000 × ß/ReD)^0.8} × ß4 × (1,000,000/ReD)^0.35

Ci(FT) = Ci(CT) + [(0.0433 + 0.0712 e -8.5L1 – 0.1145 e -6.0L1] × (1 – 0.23 × (19,000 × ß/ReD)^0.8) × β4/(1 – β4) - 0.0116 × {2/[D × (1-ß)] - 0.52 × (2/[D × (1-ß)])^1.3} × ß1.1 × {1 - 0.14 × (19,000 × ß/ReD)^0.8}

Ci(CT) = 0.5961+ 0.0291 × ß^2 - 0.2290 × ß^8

If pipe diameter is less than 2.8 inches, the Ci(CT) orifice calculation factor is modified as follows with D in inches:

Ci(CT) = Ci(CT) + 0.003 × (1-ß) × (2.8 - D)

ReD    = Reynolds number for the pipe, dimensionless = 𝜌₁𝑣𝐷/μ 

𝑣         = fluid velocity

D        = pipe diameter

μ         = viscosity

Ev       = velocity of approach factor = (1 - ß^4)^-0.5

Y1       = expansion factor (upstream tap) = 1 – (0.3625 + 0.1027×β^4 + 1.1320 × β^8) × {1 – [P2/P1]1/κ}

ß.         = diameter ratio, (d/D)

κ.         = isentropic coefficient

P1, P2 = pressure at upstream and downstream tap respectively

Orifice Meters with Pipe Taps:

Current AGA/API Standard does not contain details of pipe tap orifice metering, but refer to the 1992 Standard (3rd Edition), which uses the factor-method for calculation of flow orifices.

For gas orifices:

Q_v =C^* √(P₁h_w)

        where

                     Qv = volumetric flowrate, ft3/hr
                     C* = orifice flow constant = Fb × Fr × Y1 × Fpb × Ftb × Ftf × Fgr × Fpv
                     P1 = upstream flowing pressure, psia
                     hw = orifice differential pressure, inches H2O at 60 oF
                     Y1 = expansion factor (upstream tap) = 1 - (0.333 +1.145×(β^2 + 0.7 × β^5 + 12 × β^12) × {(ΔP/P1 × 𝜅}

                     Fb   = basic orifice factor  = 338.178d2 K0 
                     Fr    = Reynolds number factor = 1 + E/ReD 

                     Fpb = base pressure factor
                     Ftb  = base temperature factor
                     Ftf   = flowing temperature factor
                     Fgr  = real gas relative density factor
                     Fpv  = super-compressibility factor
                     K0   = coefficient of discharge at infinite Reynolds number = Ke/[1 + 15 x E/1,000,000/d

                     Ke   = coefficient of discharge when Reynolds number = 1,000,000 x d/15
                             = 0.5925 + 0.0182/D + (0.44 - 0.06/D) × ß^2 + (0.935 + 0.225/D) × ß^5 + 1.35 × ß^14 + (1.43/D^0.5) × (0.25 - ß)^2.5

             E     = d × (905 - 5000 × ß + 9000 × ß^2 - 4200 × ß^3 + 875/D)

             ß     = diameter ratio, (d/D)

             κ      = isentropic coefficient

For liquid orifices, the equation reduces to:

Q_v =C^* √h_w

         where

            Q_v          = volumetric flowrate, GPH 

            C^*             = orifice flow constant  =  F_bF_rF_pbF_tbF_tfF_gr

From K₀ and K_e above it can be shown that the discharge coefficient at any Reynolds number is:

                                                             K = K_o x (1 + E/R_eD)

ISO-5167 Orifice
 
ISO-5167 is based on the International Standard Organisation Standard ISO-5167. Orifice Size is calculated from given flowrate and pressure drop, Flowrate is calculated from given size and pressure drop and Pressure Drop requires orifice size and flowrate. Different taps can be selected: Flange Taps, D and D/2 or Corner taps. Fluids include gases: Natural Gas (Specific Gravity must be provided), Air and Nitrogen, or liquids: Crude Oil, Water, Methanol, Mono-ethylene Glycol, Diethylene Glycol and Triethylene Glycol. In addition, selecting orifice material will adjust the sizing parameter of the orifice depending on temperature.

The rate of mass flow is related to the pressure differential according to:

   Qm = C x E x ¶/4 x d² x √(2 x DP x 𝜌₁) 

where  

                 Q_m           =     mass flow rate (kg/s)

                 C            =     discharge coefficient                  = alpha/E

                  E           =     velocity of approach factor         =  (1- ß⁴)^-0.5       

                  d            =     orifice diameter at actual flowing conditions, m

          DP         =     Pressure drop across the orifice (P1 - P2), Pascal                

          𝜌₁           =     density of flowing fluid measured at upstream tap, kg/m³

                  alpha      =     flow coefficient = CE

                  ß             =     d/D

The discharge coefficient, C, and the expansion factor are determined empirically:

C = 0.5961 + 0.0261ß² - 0.216ß⁸ + 0.000521 × [10⁶ × β /R_eD]^0.7 + (0.0188 + 0.0063A)ß^3.5 × [10⁶/R_eD]^0.3 + (0.043 + 0.080e^-10L₁ - 0.216e^-7L₁) × (1 - 0.11A) × (β⁴/(1 - β⁴)) - 0.031(M’₂ - 0.8M’₂^1.1) β^1.3

If D<71.12 mm (2.8 in), the following term must be added to the above equation:

                + 0.011(0.75-β) x (2.8-D/25.4) (D in millimeter)

where

          R_eD        = pipe Reynolds number

          M’₂      = 2L’₂/(1-β)

          A          = (19000β/R_eD)^0.8                 

For corner taps:            L₁ = L’₂ = 0

For D and D/2 taps:     L₁ = 1.0 and L’₂ = 0.47

For flange taps:            L₁ = L’₂ = 25.4/D (D in millimeter)

The expansion factor is given as:

                                                          Epsilon = 1 – (0.351 + 0.256ß⁴ + 0.93ß⁸){1-[p₂/p₁]^1/κ }

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Restrict-Ori

Restriction orifice calculations are performed according to R. W. Miller's "Flow Measurement Engineering Handbook".

Gas Restriction Orifices

For gases restriction orifices are calculated based on critical flow, which means that sonic velocity (critical flow) exists at the orifice throat, and further decrease in the downstream pressure will not increase the mass flow rate.  

For critical flow the basic mass flow rate equation is:       

𝑄𝑚 = 1336.485 × 𝐶 × 𝑑² × √(𝑍 × Y_CR  × 𝜌 × F_TP × P)                            

where

                 𝑄𝑚       =     mass flow rate, lb_m /h

                 C         =     critical discharge coefficient

                 d          =     orifice diameter at flowing conditions, in

                 Y_CR      =     critical flow function

                F_TP         =     total pressure correction factor to adjust for difference between static pressure read at the pipe wall (Manometer) and total pressure of the fluid 

                 and      Z, 𝜌  and P are measured at flowing upstream conditions

For ß-ratios less than 0.5 the total pressure correction factors are approximated by:

                                           F_TP = {1 - k/2[2/(k+1)]^{[(k+1)/(k-1)]} × ß⁴}^-1                                                      

                                           Y_CR = {k/Z×[2/(k+1)]^{[(k+1)/(k-1)]}}^0.5                                                            

where

                 k          =     isentropic coefficient at flowing conditions

Assuming steady isentropic flow, critical flow (choked flow) occurs when:

                                           P₂/P₁/F_TP < [2/(k+1)]^[k/(k-1)]                                                    

where

                 P₁             =     pressure upstream orifice 

                 P₂             =     pressure downstream orifice

By assuming sharp-edged orifices with plate thickness to bore diameter between 1 and 6 the discharge coefficient is a constant given as:

C = 0.83932

Liquid Restriction Orifices

Liquid choked flow occurs if a cavitation barrier exists within an orifice.  Only upstream pressure increases can increase flowrates.  

However, generally for liquids, the vapor pressure will be lower than atmospheric pressure (except volatile fluids like light crude oils and methanol), so choked flow likely will not occur.  Therefore, in this app, if vapor pressure is found to be lower than given downstream pressure, the pressure drop is calculated based on control valve pressure drop calculations:

Choked Flow (Critical Flow) (P₂ < P_V):                              ΔP =     P₁ - P_V              

Non-Choked Flow (Non-Critical Flow (P₂ >= P_V):             ΔP =     P₁ - [0.96 – 0.28 * (P_V /P_Crit)] * P_V 

Thick square-edged orifices are used as they are inexpensive. 

The sizing and flowrate equation used for liquids is:

Qm = C × E × ¶/4 × d² × √(2 x DP x 𝜌₁)                                

where   

𝑄𝑚        =          mass flow rate, lb_m /h

C          =          critical discharge coefficient

E          =          velocity of approach factor = (1- ß⁴)^-0.5

d          =          orifice diameter at flowing conditions

DP        =          Pressure Drop, calculated as per above, depending on P_v and P₂, Pa (Pascal)

P₁         =          Upstream orifice pressure, Pa

P₂         =          Downstream orifice pressure, Pa

P_V         =          Vapor Pressure, Pa

                               𝜌₁           =          density of fluid at upstream pressure, kg/m³

  For non-choked flow, the app will estimate a Cavitation Index:

                                                            CI = (P₂ – P_v) / (P₁ – P₂)                                  

where subscripts 1 and 2 refer to upstream and downstream pressures respectively.

If the Cavitation Index is less than the acceptable cavitation level, sigma, cavitation is likely to occur at the orifice outlet, and the app will give a warning and the calculated cavitation index (CI) is shown compared to acceptable index, sigma.

Assuming square-edged orifices with plate thickness to bore diameter less than 6 with a minimum of 0.125 in (3 mm), the liquid restriction orifice constant used in this app is:

                                                                        C = 0.6

Oi&GasPVT calculates physical properties for gases (Natural Gas, Air and Nitrogen) and liquids (Crude Oil,

Water, Methanol (MeOH), Mono-ethylene Glycol (MEG), Di-ethylene Glycol (DEG) and Tri-ethylene Glycol (DEG)).

Gas properties:

• Compressibility factor (Z-factor - gas deviation factor)

• Molecular weight

• Density

• Viscosity

• Thermal compressibility

• Thermal conductivity

• Specific heat capacity

• Ideal heat capacity ratio, Cp/Cv

• Real isentropic coefficient, k

• Gas formation volume factor (natural gas only)

• Pseudo Critical properties

• Pseudo Reduced properties

Liquid properties:

• API gravity (Crude Oil only)

• Molecular weight

• Density

• Viscosity

• Thermal compressibility

• Thermal conductivity

• Specific heat capacity

• Surface tension

• Bubble point pressure

• Solution Gas-Oil-Ratio (oil and water)

• Formation Volume Factor (oil and water)

• Pseudo Critical properties

• Pseudo Reduced properties

Standard conditions are defined as 60 °F (15.6 °C) and 14.696 psia (1.01325 Bara).

Calculations are based on customary units unless noted (Temperature = °F, Pressure = psia, Density = lb/ft3, etc.). Generally, pseudo-critical properties and pseudo-reduced properties are used throughout the app.

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