About This Item
- Full TextFull Text(subscription required)
- Pay-Per-View PurchasePay-Per-View
Purchase Options Explain
Share This Item
The AAPG/Datapages Combined Publications Database
GCAGS Transactions
Abstract
Top Seal Character and Sequence Stratigraphy of Selected Marine Shales in Gulf Coast Style Basins
William C. Dawson and William R. Almon
Texaco, Inc., 3901 Briarpark Dr., Houston, TX 77042
ABSTRACT
Marine shales are top seals for approximately seventy percent of documented hydrocarbon accumulations, but represent one of the least studied elements of petroleum systems. Sealing capacity is determined from laboratory measurements (high-pressure mercury injection capillary pressure), which are used to calculate hydrocarbon column heights. The largest interconnected pore throats control seal capacity. Pore throat size is influenced by numerous compositional (mineralogy, total percentage of clay, and organic enrichment) and textural (fissility, silt content, and degree of compaction) aspects of shales. Mineralogic analyses indicate an average composition of: 65% clay; 19% quartz; 4% feldspars; 5% pyrite; and 7% accessory constituents (authigenic carbonates, glauconite, bioclasts, and carbonaceous debris). The TOC of these shales ranges from 0.79 to 4.00 (wt %). In general, seal capacity increases with increasing clay and organic content and decreases with increasing detrital silt content. The analyzed Tertiary shales (140 samples) record middle neritic to outer neritic/bathyal paleoenvironments of deposition.
Mercury injection capillary pressure (MICP) data indicate that maximum top seal capacity ranges from 735 ft to 2,305 ft (oil column) with hydrocarbon saturations in the seal of 10 percent. Calculated seal capacity typically exceeds hydrocarbon column heights by a factor of 5 to 20 times. Consequently, top seal capacity is not a significant risk in structures having four-way closure. The interpretation of seal analysis data within a sequence stratigraphic context reveals a systematic trend in top seal capacity. Shales occurring in the uppermost transgressive systems tracts and maximum horizons are excellent top seals. Shale samples from the lower part of transgressive systems tracts are good to excellent seals, whereas shales within highstand systems tracts have moderate to good sealing capacity. Some condensed intervals contain exceptional top seals.
Pay-Per-View Purchase Options
The article is available through a document delivery service. Explain these Purchase Options.
Watermarked PDF Document: $14 | |
Open PDF Document: $24 |