Effect of Solution-Gas-Oil-Ratio on Performance of Solution Gas Drive in Foamy Heavy Oil Systems

Abstract

Foamy oil flow occurs in primary depletion of heavy oil reservoirs as has been demonstrated in many laboratory experiments. It is thought to be an important recovery mechanism in several heavy oil reservoirs in Canada and Venezuela, which have shown higher recovery factors compared to what is expected from the normal solution gas drive theory. This work investigates the effects of several process parameters on oil production rate and recovery factor in foamy solution gas drive. The parameters examined included gas-oil-ratio (GOR), saturation pressure, the rate of pressure depletion and the drawdown pressure. GOR was varied independent of saturation pressure by using different gases, namely, methane, ethane and carbon-dioxide. Each foamy oil system was fully characterized by measuring gas oil ratio, oil compressibility, live oil viscosity, surface tension and foam stability. A total of 10 solution gas drive experiments were carried out in 2-meter long sand-pack equipped with several intermediate pressure taps using different solution gases and varying pressure decline rates. The results show that the foamy solution gas drive performance is affected by solution gas-oil-ratio in a counterintuitive manner. The oil recovery decreased with increasing gas oil ratio at fixed saturation pressure. At the same rate of pressure depletion, higher oil recovery was obtained with methane saturated oil than with carbon dioxide saturated oil. Ethane, which had the highest solubility, provided the lowest recovery factors. It was also found that the oil recovery factor did not decrease significantly when the saturation pressure was decreased from 3,500 kPa to 2,100 kPa. An analysis of all 10 depletion tests revealed that the most important factor that affects the oil recovery performance was the drawdown pressure, which was defined as the difference between the average sand-pack pressure and the production port pressure. Results obtained with different solution gases and widely varying depletion rates fell on the same trend line when the final recovery factor was plotted against the average drawdown pressure applied during the depletion.

Gas Recharging Process Study in Heavy Oil Reservoirs

“…Table 4.1 29 displays the dimensions of the core holder, the sand and the fluid properties of glass beads and sand packed 18m in length cores. It should be noted that the both core lengths are around 18m which are much bigger than the cores normally used in other studies 16,[20][21][22][23][24][25][26][27][28] . In addition, permeability difference between the two cores should be noticed as well; 11.8D and 1.9D for the glass beads and sand packed cores, respectively.…”

“…Since 1963, a successful natural gas-injection project in a heavy oil reservoir (14)(15)(16)(17)(18)(19)(20) located in Eastern Venezuela was conducted, reported by Garcia 3 , gas injection applied to heavy oil deposits began to be thought attractive and possible. Dynamic miscibility and gravity segregation both contributed to the high recovery.…”

“…Since the early 1963, a natural-gas-injection project was successfully conducted in a heavy oil reservoir (14)(15)(16)(17)(18)(19)(20) Although much research work on improving oil recovery is ongoing for years, most of the experiments to date were applied at small scale core samples. It is always difficult at the laboratory level to carry out such experiments in real representative field condition, but it is no doubt that larger scale experiment is one step closer 29 to the reservoir scale and is very helpful to understanding the prevailing mechanisms which may occur in the reservoir.…”

“…It is always difficult at the laboratory level to carry out such experiments in real representative field condition, but it is no doubt that larger scale experiment is one step closer 29 to the reservoir scale and is very helpful to understanding the prevailing mechanisms which may occur in the reservoir. To the best of our knowledge, the longest cores [16][17][18][19][20][21][22][23][24][25][26][27][28] which have ever been used in the past are two 18m in length cores (glass beads packed and sand packed separately) tested by Goodarzi 17,19 and Shi 18 .…”

Experimental Study on Factors Affecting the Performance of Foamy Oil Recovery

“…According to the observation of the glass micromodel experiment, Bora [3] proposed that bubble formation in a dissolved gas driven reservoir generally includes five processes: supersaturation, bubble nucleation, bubble growth, bubble merging and splitting. Busahmin et al [4] conducted 10 experiments with different kinds of gas components to study their performance on solution gas drive in foamy heavy oil system. It turned out that ethane provided the lowest recovery, and methane obtained a higher recovery than CO 2 .…”