Chapter 2 Pressure-Volume-Temperature for Oil PVT analysis – PVT relationship

Three main oil PVT parameters The three main parameters required to relate surface to reservoir volumes for an oil reservoir: - Rs: The solution (or dissolved) gas-oil ratio - Bo: The oil formation volume factor - Bg: The gas formation volume factor

Definition of the basic oil PVT parameters - Rs: The solution (or dissolved) gas-oil ratio at reservoir P&T - Bo: The oil formation volume factor - Bg: The gas formation volume factor Note : Standard Condition For T = const.

Determination and Conversion of PVT Data Determination of three main oil PVT parameters(RS, Bo, Bg) -> PVT = f (P only) by routine laboratory analysis Conversion of PVT data, as presented by the laboratory, to the form required in the field, Laboratory - an absolute set of measurements Field - depend up as the manner of surface separation of the gas and oil

The complexity of Oil PVT For gas, PVT relation -- Simple relation For oil, PVT relation > Complex; PVT parameters must be measured by laboratory analysis of crude oil samples. >Relationship between surface and reservoir hydrocarbon volumes.

The complexity of Oil PVT The complexity in relating surface volumes of hydrocarbon production to their equivalent volumes in the reservoir can be appreciated by considering the following figures: Undersaturated oil saturated oil gas saturated oil + free gas (or liberated solution gas) They are traveling in reservoir at different velocity

How to divide the observed surface gas production into liberated and dissolved gas volumes in the reservoir? Control in relating surface volumes of production to underground withdrawal is gained by knowing the three oil PVT parameters which can be measured by laboratory experiments performed on samples of the reservoir oil, plus its originally dissolved gas.

Oil Reservoir & Surface Volume – Above Bubble Point Undersaturated oil

Oil Reservoir & Surface Volume – Below Bubble Point Saturated oil gas saturated oil + free gas (or liberated solution gas) They are traveling in reservoir at different velocity

The instantaneous gas-oil ratio or producing gas-oil ratio

Bo as Function of Pressure

Rs as Function of Pressure

Bg and E as Function of Pressure

Producing Gas-oil Ratio (R) as Function of Pressure

Exercise 2.1 - Underground withdrawal Given: measured at t during the producing life Calculate: (1) Underground withdrawal rate expressed in terms of x & y (2) Underground withdrawal rate if pres = 2400 psia , qo =2500 STB/D , qg=2.125 MMscf/D and PVT data in fig. 2.5(a)~(c) (p.51) or table 2.4 (P.65) (3) Pressure gradient of oil =? if

(1) R = y/x = qg/qo [=] SCF/STB p is known  Bo ; Rs ; Bg Underground withdrawal

P = 2400 psia from table 2.4  Bo =1.1822RB/STB Rs = 352 SCF/STB Bg = 0.0012 RB/SCF x = qo = 2500 STB/D; y = qg = 2.125 MMSCF/D

(3) To find , applying mass balance, such as Mass of 1 STB of oil Mass of Bo RB of oil + = + Rs scf dissolved gas at dissolved gas in the standard condition reservoir condition