Oil tends to reappear in old oil pools and empty wells. Russian experts suggest an explanation for his interesting phenomenon.

Earth’s crust looks like a layered pancake – it’s made of solid layers and crack-porous layers, pierced with various fluids, including oil. In certain localities the crust bears dense networks of cracks and faults. Said faults turn into nearly horizontal cavities, forming webby structures. All this complex system is in permanent motion due to tectonic forces. Layers move and act like a rubber bulb – fluids, flowing from surrounding porous materials, start filling cavities. Significant tectonic stresses can cause fluids moving on long distances.

Researchers consider this mechanism of fluid movement in Earth’s crust to be most intensive and universal among all possible similar mechanisms. Mentioned mechanism applies both to faults and to thin fractured layers, which stretch to considerable distances. Crust fluctuations make fluids flow towards any possible direction, whether it’ll be up or down. Liquids travel along extended systems of cavities and fractures, which are located as deep as 10-15 kilometers.

Fluid movement, caused by extension of crust inner cavities, is oscillatory – it means that oil either arrives or ebbs. Such parameters like oscillating behaviour and oscillation period strongly depend on size of disturbed area. Large porous layers have long oscillation period, which can reach as much as 10 thousand years. Faults usually show shorter oscillation period, lasting between thousand years and hundreds, or even tens of years in case when fault zones are located near the surface.

Scientists have studied migration process of hydrocarbons from oil-bearing strata to upper layers in several regions. As an example they took Romashkinskoye oil deposit located in Tatarstan Republic. Volume of produced oil has significantly increased compared to previously approved reserves. Official data of oil-producing companies show that over 65% of Tatar oil is produced at old deposits, previously considered being almost depleted (depletion reached 80%). However, extension of already known deposits brought oil extracting enterprises additional 50% of oil during last 25 years.

  As for Romashkinskoye oil deposit, researchers have found old exhausted wells, where resumed influx of oil or mixture of water and oil has been detected. Areas of oil deposits and oil reserves grow with increase of fault network density. Scientists discovered an interesting, thus worth mentioning fact – territories of large Romashkinskoye oil deposit have sedimentary cover, which average thickness doesn’t exceed 2 kilometers – thus said deposit has weak oil potential. Most probably additional oil comes from Preduralsky foredeep.

Scientists tend to think that resume of old oil deposits is much more profitable and effective than expensive geological exploration works at new places.

Source:
    Russian Science News

Kizilova Anna