Abstract
Nowadays, extra heavy oil reservoirs in the Orinoco Heavy-Oil-Belt in Venezuela are exploited via cold production process, which present different production performance in well productivity and primary recovery factor. The purpose of this study is to investigate the causes for such differences with the aspect of foamy oil mechanism. Two typical oil samples were adopted from a shallow reservoir in western Junìn region and a middepth reservoir in eastern Carabobo region in the Belt, respectively. A depletion test was conducted using 1D sand-pack with a visualized microscopic flow observation installation for each of the oil samples under simulated reservoir conditions. The production performance, the foamy oil behaviour, and the oil and gas morphology were recorded in real time during the tests. The results indicated that the shallow heavy oil reservoir in the Belt presents a weaker foamy oil phenomenon when compared with the middepth one; its foamy oil behaviour lasts a shorter duration with a smaller scope, with bigger bubble size and less bubble density. The difference in foamy oil behaviour for those two types of heavy oil reservoir is caused by the difference in reservoir pressure, solution GOR, asphaltene content, etc. Cold production presents obvious features of three stages under the action of strong foamy oil displacement mechanism for the middepth heavy oil reservoir, which could achieve a more favourable production performance. In the contrary, no such obvious production characteristics for the shallow heavy oil reservoir are observed due to weaker foamy oil behaviour, and its primary recovery factor is 9.38 percent point lower than which of the middle heavy oil reservoirs.
Highlights
Extra heavy oil in the Orinoco Heavy-Oil-Belt in Venezuela nowadays is exploited via solution gas drive process or socalled cold production and presents some certain foamy oil behaviour [1, 2]
Different reservoirs in the Orinoco Belt vary in well productivity and primary recovery factor, due to difference in reservoir buried depth, reservoir properties, crude oil viscosity, original dissolved gas oil ratio (GOR), and due to the difference in foamy oil performance, that is, strong or weak foamy oil behaviour
In the Orinoco Belt, the buried depth of the main oilbearing formations is approximate 300-500 m in Boyacá and Junìn regions, which is classified into shallow reservoir type, and 800-1200 m in Ayacucho and Carabobo regions, which is classified into middepth reservoir type
Summary
Extra heavy oil in the Orinoco Heavy-Oil-Belt in Venezuela nowadays is exploited via solution gas drive process or socalled cold production and presents some certain foamy oil behaviour [1, 2]. Different reservoirs in the Orinoco Belt vary in well productivity and primary recovery factor, due to difference in reservoir buried depth, reservoir properties, crude oil viscosity, original dissolved gas oil ratio (GOR), and due to the difference in foamy oil performance, that is, strong or weak foamy oil behaviour. In some shallow heavy oil reservoirs in Junìn region, the cold production performs relatively poorly, with an averaged well productivity less than 70 t/d and a primary recovery factor of no more than 6%. Study on foamy oil behaviour in those heavy oils is rare It is the purpose of this paper to investigate the foamy oil behaviour in such shallow heavy oils in western Junìn region and compare with middepth heavy oils in the eastern region to deeply understand the reason why the cold production performs unfavourably and provide the basis for seeking strategies to improve the productivity. Two typical oil samples are adopted for the comparison studies; one is from a shallow reservoir T in western Junìn region, and the other is from a middepth reservoir M in eastern Carabobo region, respectively
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call