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Lateral fluid flow in a compacting sand-shale sequence: South Caspian basin

January 1, 1988

The South Caspian basin contains both sands and shales that have pore-fluid pressures substantially in excess of hydrostatic fluid pressure. Pore-pressure data from the South Caspian basin demonstrate that large differences in excess hydraulic head exist between sand and shale. The data indicate that sands are acting as drains for overlying and underlying compacting shales and that fluid flows laterally through the sand on a regional scale from the basin interior northward to points of discharge. The major driving force for the fluid movement is shale compaction. We present a first- order mathematical analysis in an effort to test if the permeability of the sands required to support a regional flow system is reasonable. The results of the analysis suggest regional sand permeabilities ranging from 1 to 30 md; a range that seems reasonable. This result supports the thesis that lateral fluid flow is occurring on a regional scale within the South Caspian basin. If vertical conduits for flow exist within the basin, they are sufficiently impermeable and do not provide a major outlet for the regional flow system. The lateral fluid flow within the sands implies that the stratigraphic sequence is divided into horizontal units that are hydraulically isolated from one another, a conclusion that has important implications for oil and gas migration.-Authors

Publication Year 1988
Title Lateral fluid flow in a compacting sand-shale sequence: South Caspian basin
DOI 10.1306/703C8EA7-1707-11D7-8645000102C1865D
Authors John D. Bredehoeft, R. D. Djevanshir, Kenneth Belitz
Publication Type Article
Publication Subtype Journal Article
Series Title American Association of Petroleum Geologists Bulletin
Index ID 70014765
Record Source USGS Publications Warehouse
USGS Organization Massachusetts Water Science Center