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AAPG GEO 2010 Middle East
Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain

Active Fluid Regime of the Basement Fractured Zones in Volga-Ural Region

Irina N. Plotnikova1

(1) Geological Faculty, Department of Geology of Oil and Gas, Kazan State University, Kazan, Russian Federation.

The parametric well Novo-Yelkhovo-20009 penetrated loosely aggregated zones of the crystalline basement including those occurring at a depth of more than 3.0 km below its top. Geophysical data indicate aggregated zones. Most of them occur at a depth of more than 5000 m. From 1991 through 1996, mud sampling was repeatedly conducted in the well at specified depths, and the gas saturation was studied. These studies showed that the amount of dissolved hydrocarbon gases and their composition changed with time. Regrettably, no production tests have yet been conducted on the loosely aggregated zones. These are supposed to contain brines and dissolved gases including hydrocarbon ones. The quantitative and compositional variations of the dissolved gas recorded in the course of the monitoring indicate its movement in the loosely aggregated zones due to possible geodynamic and pressure changes in these zones. This means that the loosely aggregated zones of the basement are geodynamically active.

The reservoir water monitoring has been conducted in five wells that have penetrated the water-saturated, loosely aggregated zones of the South Tatarstan Arch’s basement. The long-term testing resulted in the production of reservoir water from the basement. The sedimentary cover in these wells is blocked by the column, which prevents water cross-flowing from the sedimentary cover. The basement remains unaffected by the development or the technogenic impact. Therefore, the monitoring of reservoir water dynamics in the basement is the monitoring of natural processes, not of the consequences of oil development in the sedimentary cover.

The time-dependent reservoir water compositional changes also prove the present-day movement of fluids. It cannot be excluded that high geodynamic activities in the loosely aggregated zones of the basement in the central portion of the South Tatarstan Arch cause periodical variations in their formation pressure and temperature regime. These processes can in turn change the reservoir water composition.

Fluid migration still takes place in the Earth’s crust of ancient platforms. This phenomenon indicates that some portions of the platforms - primarily, their margins - periodically resume tectonic activities. The fluid dynamic activity of the crust define the processes in the sedimentary cover. It affects the development of the sedimentary basin during the sedimentation period, and the formation of mineral deposits.