PETE 310

Lectures # 11

Real Gases from SPE 26668

SPE Paper 26668

Real Gas Equation

Evaluation of Ppc & Tpc when composition is known

Evaluation of Ppc & Tpc when gas specific gravity is known

New ways of handling corrections for N2, CO2, H2S

This Methodology Replaces Book Method

Corrections for impurities MUST be handled using the method in paper

Determination of Ppc and Tpc from this paper replaces method in book

Watch for equations to be used in THIS PRESENTATION

Pseudocritical Properties

Defined once K and J are evaluated

Different methods to evaluate K and J

Given compositions

Given specific gravities only

Corrections for non-hydrocarbon components is included in expressions

Pseudocritical Properties

Compositions known & C7+ includes corrections for

H2S, N2 and CO2

and

Pseudocritical Properties

Watch index !!!

And

In this order

Pseudocritical Properties

Compositions known including corrections for H2S, N2 and CO2

And

In this order

Coefficients in Equation 4

Pseudocritical Properties

Specific gas gravity & composition of impurities is known

i = H2S, N2 and CO2- 3 major impurities)

Coefficients in Equation 6

Note on Gas Gravity

Do not confuse this Gas Gravity with the “gas gravity” at reservoir conditions

R2 - Statistical Evaluation of Goodness of Fit (How well you fit the data)

2n

1i

i )YY(SSR

2n

1i

ii )YY(SSE

SYY

SSRR ionDeterminat of tCoefficien 2

SSESSRSSY

sum of squares of (predicted – average)

sum of errors squared(true value – predicted value)

When R2 is close to 1 SSE is close to zero!

sum of errors squared is nearly zero

Appreciate Estimates…

A Faster Procedure (but less accurate)

Given gas specific gravity read J

Given compositions of N2, CO2, H2S correct J using charts

J = J + sum(Correction_i)

Note the corrections are negative

A Faster Procedure (but less accurate)

Given gas specific gravity read K

Given compositions of N2, CO2, H2S correct K using charts

K = K + sum(Correction_i)

Note the corrections are negative

The Chart for J

The Corrections for J

The Chart & Corrections for K

The Procedure

Determine Tpc and Ppc

Given gas composition

Given gas gravity & compositions of impurities

At given p and T determine Tpr and Ppr

Determine z for the gas requested

Evaluate z-factor…

Practical Applications …

Sequester CO2 in depleted reservoirs

Design gas storage equipment (cylinders, tanks)

Transportation

Material balance in Reservoir Engineering (PETE 323)

Exercise in Class

Determine the density of an acid gas at 3,500 psia and 220 oF

The gas contains 5% CO2 and 15% H2S and has a specific gravity of 1.4

Questions to think

What errors could you have in your predictions if the corrections for impurities are neglected?

How good are these new correlations compared with the existing ones?

READ SPE 26668 paper for additional details