Estimation of Solution GOR of Black Oils

Abstract

Summary. An empirical equation was developed to estimate stock-tank GOR from field data for black oils. Solution GOR at or above bubblepoint pressure can be obtained as the sum of the estimated stock-tank GOR and the measured separator GOR. The equation was derived with data from two-stage separations of 301 black-oil samples. Introduction Volumetric and material-balance calculations of oil in place require estimates of oil FVF and bubblepoint pressure. Several correlations, the most applicable of which was proposed by Standing, I are available for determining bubblepoint pressure and oil FVF when an estimate of solution GOR is available. Frequently solution GOR, Rsb, is estimated for pressures at or above the bubblepoint by setting its value equal to the initial producing GOR. However, the initial producing GOR often does not include gas vented from the stock tank. This omission can cause the estimate of Rsb to be low by 20 % or more. 2 The inaccurate estimate of Rsb then introduces error into estimates of bubblepoint pressure and FVF, and hence into oil-in-place calculations. This paper presents a method of using readily available field data to obtain an accurate estimate of Rsb. Total producing GOR, R, is equal to the sum of stocktank GOR, Rst, and separator GOR, Rsp.

Rigorous Modeling of Solution Gas–Oil Ratios for a Wide Ranges of Reservoir Fluid Properties

“…Al-Marhoun [9] developed an empirical correlation applying data gathered from the Middle East region. In 1990, Rollins et al [18] proposed an empirically derived method to calculate the stock-tank gas-oil ratio as a function of oil API gravity, separator pressure and temperature, and gas gravity. In the same year, Sutton and Farshad [19] reviewed several PVT correlations and compared the accuracy of each model for several PVT parameters for application in the Gulf of Mexico.…”

Implementing ANFIS for prediction of reservoir oil solution gas-oil ratio

“…By rearranging and solving the correlation for solution gas oil ratio a new equation is obtained which can be used for gas solubility prediction. In 1990, Rollins et al (Rollins et al, 1990) proposed an empirical equation to estimate gas oil ratio (GOR) of stock tank utilizing data from two stage separators of 301 samples of black oil. Assuming stock tank gas oil ratio as a function of stock tank oil specific gravity, separator-gas specific gravity, separator pressure and separator temperature, they proposed a graphical correlation for determination of total solution gas oil ratio.…”

Prediction of Bubblepoint Pressure and Bubblepoint Oil Formation Volume Factor in the Absence of PVT Analysis

“…Moreover, several correlations developed by Labedi (1990), Rollins et al (1990), Dokla and Osman (1992), Macary and Batanony (1992), Velarde et al (1999), Petrosky and Farshad (1998) and McCain et al(1998) use flash separator gas specific gravity (γ gSP ), while others use total gas specific gravity, like those of Standing (1947), Borden and Rzasa (1950), Lasater (1958), Elsharkawy and Alikhan (1997), Glaso (1980), Mazandarani and Asghari (2007). Other correlations use weight average specific gas gravity of the separator and stock-tank vent gas.…”

“…To estimate bubblepoint pressure and bubblepoint oil FVF, he suggested Sanding (1977) correlations, Equations 5 and 6 in conjunction with Rollins et al (1990) …”