A very important result of exploration in recent years in Turkmenistan has been the discovery of new gas fields in the Kumbet-Karadzhaulak zone of highs, which is located on the outer border zone of the Kaakhka depression of the Cis-Kopet Dag foredeep. The Kopet-Dag is the eastward continuation of the Alpine fold belt, and its foredeep is along its north flank. These highs occur on monoclinally dipping Jurassic and Lower Cretaceous sediments.
Upper Jurassic evaporites consist of Kimmeridgean-Tithonian salt and anhydrite and upper Oxfordian-Kimmeridgean anhydrite. These evaporites separate two independent plays: Valanginian above the evaporites and Oxfordian below them.
According to seismic surveys buried local highs of the Kumbet Range are expressed without significant shift in the sub-salt and supra-salt sections. Dimensions of these structures are 5-10 by 3-5 km, and amplitudes increase with depth from 20-30 to 40-90 m. Recognized in the sub-salt of the Karadzhaulak Range are the Yelkov (8 by 3 km, amplitude of 40 m) and Karadzhaulak ( (7 by 2 km, amplitude of 40 m) highs and the Z. Karadzhaulak (5 by 2 km) structural nose. In the supra-salt section these highs open up into structural noses.
The Karadzhaulak, Z. Karadzhaulak, and V. Kumbet gas-condensate fields have been discovered in two supra-salt plays: Tithonian and Valanginian.
The Tithonian carbonate gas-oil play is composed of dolomites, anhydrites, limestones, and clays. The regional seal is a Valanginian clay. The gas occurs in the "Beurdeshik" horizon, which is productive in the 4300-4400 m interval. This unit consists of porous-cavernous dolomite, which has high porosity and permeability. Testing yielded 230,000 cubic meters per day at Karadzhaulak and 134,000 cubic meters per day at V. Kumbet. It appears that the gas-condensate pools fill the traps to the spill point. And it is possible that some of the pools extend beyond the limits of the traps.
The Valanginian carbonate-clastic oil-gas play is overlain by Hauterivian clays. It is characterized by a poly-facies section: marine clays, massive limestones, and shallow-water dolomitized limestones. Gas productivity has been established in the V. Kumbet area by testing porous-cavernous and fractured carbonates at a depth of 4230 m, where gas was recovered at 100,000 cubic meters per day with condensate.
It is possible that oil will also be found in the Kumbet-Karadzhaulak zone of highs, as is indicated by the high gas-condensate content.
Although the first discoveries have been made in the supra-salt section, the sub-salt is still the most favorable play. This is the Oxfordian carbonates, which have been penetrated by but few drill holes. This prediction is based on favorable structural and lithofacies conditions and the regional productivity of the Upper Jurassic over a wide area in southeastern Turkmenistan.
Taken from Ashirmamelov and others, 1986; digested in Petroleum
Geology, vol. 23, no. 11/12, one structure map.
Copyright 2002 James Clarke. You are encouraged to print out this
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