Steam Injection Experiences in Heavy and Extra-Heavy Oil Fields, Venezuela

Abstract

Abstract The exploitation and development of large heavy and extra heavy oil fields in Venezuela represents one of the largest hydrocarbon accumulations in the world. These deposits can be found at the Orinoco Heavy Oil Belt in Eastern Venezuela, the Bolivar Coast Fields in Western Venezuela and Santa Barbara and Pirital Fields in the Northeast of Venezuela. The Orinoco Heavy Oil Belt represents a 90% of the discovered extra-heavy oil in the country. Enormous deposits of hydrocarbons can be found in "Cerro Negro", "Machete", "Hamaca" and "Zuata" that belong to the Orinoco Heavy Oil Belt. These fields contain extra-heavy crude of 8 to 9 °API, an oil viscosity of 8,500 cp, an original depth of 2,900 ft and a thickness of 217 to 287 ft. The sand depositional environments are originally fluvial or deltaic and laterally discontinuous. Santa Barbara Field contains heavy oil crude of 16 to 19 °API, an oil viscosity of 510 cp, a depth of 200 to 1,150 ft and sand thickness of 40 to 253 ft. The fields come from delta derived sandstones enviromentals. Bachaquero, Lagunillas and Tia Juana Fields in the Bolivar Coast Field contain heavy crude of 11 to 15 °API, viscosity of 100 to 10,000 cps, depth of 1,000 to 3,000 ft and sand thickness of 50 to 300 ft. The sand consists of non-marine sediments, eventual transgressions and conglomerate sandstones depositional environments. The fields were studied to extract information about successful application and evaluation of cyclic steam stimulation (CSS). In the Northern part of Tia Juana Field where the viscosity was higher than expected (typically 20,000 cp), a steam assisted gravity drainage (SAGD) Pilot was implemented. Statistical analysis allowed the quantification of the parameters that affect the incremental recovery factor. As a result, it was found that the basic controls are °API, viscosity, depth, thickness and well spacing. Thermal recovery processes are mainly applied to deposits less than 1,100 m of depth, oil viscosity greater than 50 cp, gravity less than 20 °API and typical well spacing of 2-5 acres. The most common applied method was cyclic steam stimulation (CSS) with a positive incremental of oil-steam ratio, from 1.5 to 6.8. Steam Assisted Gravity Drainage (SAGD) in horizontal wells was applied increasing significantly the recovery efficiency, higher than 50%.