Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Best Practices with Exploration and Production of Oil and Gas from Basement Reservoirs
(1) Tullow Oil Angola, Luanda, Angola.
Basement rocks such as fractured and weathered granites are important oil and gas reservoirs in a number of countries and serve as a reminder that in areas where basement is not too deep, basement should be considered as a valid exploration objective.
Best practices for producing oil and gas from basement include:
1) The necessity to drill production wells near-perpendicular to the dominant fracture system.
2) The need for focused 3D seismic coverage to highlight fracture systems in basement.
3) Extensive core coverage is needed to provide information on the rock types and the reservoir parameters.
4) Development wells must be sufficiently deep to fully drain the reservoir (e.g. wells in the La Paz field in Venezuela typically are drilled 500 meters into the basement).
5) There are a number of cases, such as the La Paz field in Venezuela where the basement oil field was discovered much later (30 years) in the life of the field, with the attention initially focused on the producing of the shallow sedimentary layer reservoirs. Accordingly, in the case where an operator is producing oil or gas from reservoirs in sediments relatively close to basement, a ‘second look’ at the basement may be warranted, especially using today’s leading edge seismic and drilling technology.
6) In a general sense, fractured granites and quartzites are the optimum basement reservoirs. Weathered granites can also be excellent reservoirs. Rocks such as schists are less attractive since they are ductile and tend to ‘smear’ when subjected to tectonic stress. The high mafic content of schists also negates the creation of secondary porosity by weathering. Likewise, granites and quartzites are more likely to provide attractive, highly porous ‘granite wash sands’ whereas eroded schists do not produce attractive reservoirs.
This author has closely followed this subject for some 30 years and shares his experience and knowledge. This paper provides examples of 'best practices'associated with the La Paz Oil Field, Venezuela, Tanjung Oil Field, Kalimantan, Beruk North East oilfield, Sumatra, basement oil fields of Viet Nam, and basement oil fields of Kansas and California.