Mixing of biogenic siliceous and terrigenous clastic sediments: South Belridge field and Beta field, California

Conference · Tue May 01 00:00:00 EDT 1990 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:6634883

Schwartz, D E ^[1]

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1. Shell Western Exploration and Production, Inc., Bakersfield, CA (USA)

The intermixing and interbedding of biogenically derived siliceous sediment with terrigenous clastic sediment in reservoirs of upper Miocene age provides both reservoir rock and seal and influences productivity by affecting porosity and permeability. Miocene reservoirs commonly contain either biogenic-dominated cyclic diatomite, porcelanite, or chert (classic Monterey Formation) or clastic-dominated submarine fan sequences with interbedded or intermixed siliceous members of biogenic origin. Biogenic-clastic cycles, 30-180 ft thick, at South Belridge field were formed by episodic influx of clastic sediment from distant submarine fans mixing with slowly accumulating diatomaceous ooze. The cycles consist of basal silt and pelletized massive diatomaceous mudstone, overlain by burrowed, faintly bedded clayey diatomite and topped by laminated diatomite. Cycle tops have higher porosity and permeability, lower grain density, and higher oil saturation than clay and silt-rich portions of the cycles. Submarine fan sediments forming reservoirs at the Beta field are comprised of interbedded sands and silts deposited in a channelized middle fan to outer fan setting. Individual turbidites display fining-upward sequences, with oil-bearing sands capped by wet micaceous silts. Average sands are moderately to poorly sorted, fine- to medium-grained arkosic arenites. Sands contain pore-filling carbonate and porcelaneous cements. Porcelaneous cement consists of a mixture of opal-A, opal-CT, and chert with montmorillonite and minor zeolite. This cement is an authigenic material precipitated in intergranular pore space. The origin of the opal is biogenic, with recrystallization of diatom frustules (opal-A) into opal-CT lepispheres and quartz crystals. Porcelaneous cement comprises 4-21% of the bulk volume of the rock. Seventy percent of the bulk volume of the cement is micropore space.

• OSTI ID: 6634883
• Report Number(s): CONF-900605-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 74:5; Conference: Annual convention and exposition of the American Association of Petroleum Geologists, San Francisco, CA (USA), 3-6 Jun 1990; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
58 GEOSCIENCES
CALIFORNIA
OIL FIELDS
RESERVOIR ROCK
GEOLOGIC FORMATIONS
MONTMORILLONITE
PERMEABILITY
POROSITY
SILTSTONES
SOURCE ROCKS
TERTIARY PERIOD
CENOZOIC ERA
CLAYS
FEDERAL REGION IX
GEOLOGIC AGES
GEOLOGIC DEPOSITS
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
MATERIALS
MINERAL RESOURCES
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PETROLEUM DEPOSITS
RESOURCES
ROCKS
SEDIMENTARY ROCKS
USA
020200* - Petroleum- Reserves
Geology
& Exploration
580000 - Geosciences