Effect of Foaminess on the Performance of Solution Gas Drive in Heavy Oil Reservoirs

Abstract

Abstract Some heavy oil reservoirs under solution gas drive show abnormally high final recoveries. One of the mechanisms to explain these phenomena is the foamy oil flow effect which occurs under certain operating conditions. It has been studied extensively, yet remains poorly understood and difficult to model. The objective of this work was to investigate the effect of oil foaminess on the performance of solution gas drive in heavy oil reservoirs. In this research, the first step was to find a foaming agent that will have a measurable effect on foam stability of a viscous mineral oil. A simple experimental procedure was developed to quantify the oil foaminess in the presence of an added foaming agent. Several depletion tests were conducted with the added foaming agent at different depletion rates using a two metre long sandpack. The experimental results showed that the increased foaminess of oil did not have a significant effect on the solution gas drive performance when the depletion rate was high. However, in a slow depletion test, the effect of oil foaminess was significant. Introduction With high oil prices and the continuous decline of conventional resources, attention is shifting towards heavy oil in many parts of the world. Six to nine trillion barrels, or more than two-thirds of the world's oil resources, are heavy viscous crudes that remain difficult to produce(1). Heavy oil promises to play a major role in the future of the oil industry. Therefore, understanding heavy oil behaviour and improving the recoveries in heavy oil reservoirs is crucial to meeting future energy demand. The high viscosity of heavy oils, typically in the range of 500 to 50,000 cP, results in low recovery factors in primary production. However, some Canadian heavy oil reservoirs produce more than what is expected by the conventional analogs. Primary recovery from these reservoirs could be as high as 15%(2). In conventional solution gas drive, the gas evolves in the pore space and connects with the gas in the other pores forming a free continuous gas resulting in higher gas rates. In heavy oil reservoirs, the gas bubbles tend to remain dispersed within the viscous oil because of the high viscosity, low diffusion rates and higher pressure gradients. This behaviour results in higher oil rates, lower gas-oil ratios and slower pressure decline within the reservoir. The production from this type of reservoir is usually accompanied by sand. The two-phase flow of oil and dispersed gas bubbles is usually referred to as foamy oil flow. Smith(3) appears to be the first researcher who provided an analysis to the anomalous behaviour of the heavy oil reservoirs under solution gas drive using field data. The most common techniques used to produce heavy oil from underground formations involve thermal recovery processes. However, extensive developments in Canada in the period from 1985 to 2005 have resulted in several new heavy oil exploitation technologies. One of the major new technologies in the last two decades is cold heavy oil production with sand (CHOPS)(4).