Diagenesis of sandstone reservoirs of Pattani basin, Gulf of Thailand
Miocene sandstones from gas fields in the Gulf of Thailand's Pattani basin provide an example of rapid decline in porosity and permeability with increasing burial depth. This decline results from rapid burial diagenesis that is related to very high geothermal gradients in the basin. Porosity loss with depth in these subquartzose sandstones results from mechanical compaction and from progressive cementation by quartz overgrowths, kaolinite, and illite. Quartz overgrowths increase with depth, indicating continuous or episodic silica cementation. Kaolinite occurs as a pore-filling cement and is abundant between the depths of 1980 and 3050 m (6500 and 10,000 ft). Minor cements include calcite, ankerite, mixed-layer illite-smectite, siderite, pyrite, chlorite, and barite. The best porosity and permeability in Pattani basin reservoirs are generally associated with large intergranular pores in sandstones between 915 and 1980 m (3000 and 6500 ft). At greater depths most interparticle pores have been occluded, and porosity is mainly secondary in origin. Skeletonized feldspars indicate progressive dissolution with increasing burial depth. In low-permeability sandstones from deeper zones (2285-3050 m or 7500-10,000 ft), porosity is mainly restricted to dissolution voids within detrital feldspars. These secondary pores are usually partly filled by authigenic kaolinite and illite, and their pore apertures are generally smaller (1-15 ..mu..m) than intergranular pore aperatures (10-75 ..mu..m). However, favorable reservoir properties may occur locally at depth where large feldspars have been leached from coarse-grained sandstones. 14 figures, 1 table.
- Research Organization:
- Unocal Corp., Brea, California
- OSTI ID:
- 6884152
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:3
- Country of Publication:
- United States
- Language:
- English
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NATURAL GAS DEPOSITS
RESERVOIR ROCK
DIAGENESIS
PERMEABILITY
POROSITY
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CLAYS
QUARTZ
SANDSTONES
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DEVELOPING COUNTRIES
GEOLOGIC DEPOSITS
MINERAL RESOURCES
MINERALS
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
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SILICON OXIDES
030200* - Natural Gas- Reserves
Geology
& Exploration