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The Volga Urals basin of Western Russia has a very long production history and consequently many of the original target reservoirs have become depleted. The Uzenskoe field is no exception. Originally placed on production in 2008 the original target layers in the lower Cretaceous formations have since depleted. It was assumed that potentially productive reservoirs exist in the overlying layers; however, these had never been evaluated. Using a variety of through-casing measurements these layers were investigated for productive potential. Integrated interpretation of the acquired data was used evaluate lithology, rock composition, saturation and porosity to identify potentially productive layers. These layers were then perforated and tested with a wireline conveyed formation tester inside casing. Fluid type was verified, samples were acquired and pressure transient analysis was performed to determine layers permeability. The entire evaluation took less than three days of rig time comparing very favorably with alternative methods. In this paper we discuss the planning, execution and interpretation of this evaluation exercise.

The Verkhnechonskoye oil and gas field in Eastern Siberia produces from a highly complex Precambrian, lower Vendian sandstone. In this reservoir there has been significant post-depositional alteration due to diagenesis, secondary porosity is common and salt, anhydrite and carbonate cementation of the porosity frequently occurs. In short, the reservoir provides substantial petrophysical challenges. In the development of a petrophysical model three specific concerns were noted. Firstly, the effects of the salt-filled pore spaces complicate the determination of porosity and therefore permeability. Secondly, it is difficult to resolve permeability predictions from logs, core and formation testers. Finally, using conventional petrophysics, even with a comprehensive suite of logs and extensive core data, it is difficult to clearly delineate gas-filled porosity from oil-filled porosity and the determination of the gas-oil contact was therefore uncertain. This paper will discuss how petrophysical data from traditional triple-combo measurements was integrated with NMR measurements, core analysis data and formation tester data including permeabilities from pressure transient analysis (PTA) to produce a coherent and robust petrophysical model for permeability prediction.

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