Three aspects of the mixed-genetic scheme of natural hydrocarbon synthesis

Keywords

• heat flow
• convective heat transfer
• Bukhara–Khiva region
• Urtabulak
• Tegermen
• deep heat and mass transfer

Summary

The authors, of Uzbekneftegaz and UzLITIneftgaz, set out the mixed-genetic hypothesis of oil and gas formation, in which deep fluids rising along channels of deep heat and mass transfer react with organic matter in sedimentary rocks, and apply it to the Bukhara–Khiva oil and gas region. To map the channels, they drew a detailed heat-flow map, a geodynamic map of the region at 1:500,000 and physical-geological models of the best-studied channels, near Urtabulak, Tegermen, Gazli and Muruntau.

The heat-flow map shows 12 local isometric anomalies of 90–120 mW/m² against a regional background of 65 mW/m², often with an off-centre maximum. Geothermal calculations show that their size and amplitude do not fit steady-state heat flow and point to convective heat transfer along subvertical channels, at permeable intersections of deep faults whose position is controlled by the buried Carboniferous palaeorift system. The anomalies coincide with temperature anomalies in the sedimentary cover, zones of abnormally high reservoir pressure and oil and gas fields.

The Urtabulak channel, crossed by deep CDP profile No. 498990688 and the Farab–Babatag deep seismic sounding profile, is modelled as a permeable zone 3–5 km wide that runs from the Moho to the lower Mesozoic–Cenozoic cover; its heat source is an old magma chamber at the crust–mantle boundary. Convective transfer stops at the base of the sedimentary cover, and above it heat reaches the surface by conduction. The Tegermen channel, on the Farab–Tamdybulak profile, has the same structure, and seismic monitoring at the Gazli field traced a subvertical cylinder of higher fracturing at 1–10 km depth beneath a local heat-flow anomaly. Calculations for water, hydrogen, methane and carbon dioxide at a minimum vertical migration rate of 1 m per year show water to be the main heat carrier. The anomalous temperature is highest directly above a channel at the base of the sedimentary cover, 30–55 °C, and falls to normal about 30 km from its axis. In all, 11 active channels were mapped in the region.

How to cite

A. A. Abidov and F. G. Dolgopolov (2001). Three aspects of the mixed-genetic scheme of natural hydrocarbon synthesis. O‘zbekiston neft va gaz jurnali (Uzbek Journal of Oil and Gas), No. 4, 2001, pp. 9–12. https://drive.google.com/file/d/18GbI0Vo_SrZ1e61rXnvhsHlQBzETXWf1/view