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M. W. Ibrahim1
(1) Target Exploration Consultants, London, United Kingdom

Abstract: Missed, by-passed, and underestimated hydrocarbon traps: Analysis of basic exploration records reveals "Un-Discovery" Wells in Libya

Global hydrocarbon exploration records attest to many early "dry holes" or "dry" anomalies becoming hydrocarbon producers or oil fields with advancement in seismic, gravity, magnetic, geochemical, risk analysis, logistics, exploration, drilling and/or production methods. Wells classified as "dry holes" at completion dates, then proved to be producers at later dates can be described as "un-discovery wells". This paper presents a case study using a quick-look method to spot potential un-discovery wells among a large number of genuine dry holes.

Anomalous geothermal gradients are known in rocks overlying hydrocarbon traps. The anomalies are mainly caused by focused migration of heat-convective subsurface fluids into shallow reservoir closures.

A quick-look analysis and mapping method of the geothermal gradient (CGG-ESTI) was tested on databases of two exploration time-frames of the Hagfa Area of central Sirte Basin, Libya:

The test found high geothermal gradient anomalies to be associated with most of the known oil and gas fields in the two exploration time frames, as well as some anomalous "dry holes". Analysis of the pre-1970 database delineated several geothermally anomalous "dry hole"; one of them was then recognised, as "un-discovery well" i.e. became a producer in 1988.

Examples of un-discovery wells from Sirte Basin are "dry holes" K1-13 of Mobil Oil Libya (now K1-NC149 a producer in Wadi Field, Block NC149 of Sirt Oil), and J1-85 of Aquitaine (now a new discovery via re-entry in Block NC177 of Lundin Oil and Red Sea Oil).

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana