Fundamental Control of Low Permeability Sandstone Reservoirs, Sirikit Oil Field Phitsanulok Basin, Thailand
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Abstract
Low permeability and porosity reservoirs were investigated in the Lan Krabu (L and M units) and Sarabop (P sand unit) formations. For this research, core description, poroperm relationships and well log characteristics including mineralogy were considered from available core data in north and south area, Sirikit Oil Field, Phitsanulok, Thailand. In the southern area, there are two good potential reservoirs; P sand and Lower Lan Krabu (LKU-M) units. The best reservoir quality is proximal delta front deposits (P sand unit) in a subaqueous environment. The conglomerate/coarse grained sandstone and laminated siltstone is up to 20-26% porosity and 600-1300 mD permeability. They were deposited with variable slope and energy and become progressively more distal delta front with finer grained and mud lamination. The second best reservoir quality is in distal delta front and mouthbar deposits in the LKU-M unit. It contains distal delta front silt interbedded with sand lenses and mouth bar sandstone with mud lamination and ripples. The mouthbar facies has good reservoir quality with 6-18% porosity and 0.05-40 mD permeability. The lowest reservoir quality is in the northern area reservoir facies that was deposited as crevasse splays in the Middle Lan Krabu (LKU-L) unit. This sandstone with interbedded mudstone facies has 8-11% porosity and low (0.05-0.45 mD) permeability.
Reservoir quality in the southern area is mainly controlled by depositional environment such as variable energy during deposition, clay content, sand body geometry and sedimentary structures. Conversely, the tight reservoirs in the northern area are mainly controlled by deposition and authigenic clay content. Other diagenetic processes, such as compaction, cementation and recrystallization, also degraded porosity.
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Copyright © 2008 Department of Geology, Faculty of Science, Chulalongkorn University. Parts of an article can be photocopied or reproduced without prior written permission from the author(s), but due acknowledgments should be stated or cited accordingly.
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