GEOSTATIC PRESSURES AND ENHANCED OIL RECOVERY

June 11/2010-2:29 PM EST.
    By: Isaac N.


    How you ask ? By what's know as Enhanced Oil recovery.

   Enhanced oil recovery is also called improved oil recovery or tertiary recovery (as opposed to primary and secondary recovery). Sometimes the term quaternary recovery is used to refer to more advanced, speculative, EOR techniques.

      E.O.R. techniques are:

     Gas re-injection is presently the most-commonly used approach to enhanced recovery. In addition to the beneficial effect of the pressure, this method sometimes aids recovery by reducing the viscosity of the crude oil as the gas mixes with it.

     Chemical injection, the injection of various chemicals, usually as dilute solutions, have been used to improve oil recovery



     Polymer-enhanced recovery, using sub-micron expanding polymers, which are  injected into faultlie/fissure areas in the well-field, where they expand slowly over 6-9 month's time to force oil out of porous rock.
          
    Microbial injection is part of microbial enhanced oil recovery  and is presently rarely used, both because of its higher cost and because the developments in this field are more recent than other techniques

   Thermal methods. In this approach, various methods are used to heat the crude oil in the formation to reduce its viscosity and/or vaporize part of the oil. Methods include cyclic steam injection, steam drive and in situ combustion. These methods improve the sweep efficiency and the displacement efficiency. Steam injection has been used commercially since the 1960s in California fields

   How do E.O.R. techniques influence geostatic pressures ?

   Geostatic pressures are determined by the weight of a column of beds. At a given depth, the geostatic stress or geostatic pressure (g) is given by a biaxial ellipsoid, with: vertical = v =d. g .h (d=density of sediment, g=gravitation, h=height of sediments)horizontal =h = confining pressure of g. The geostatic stress ellipsoid varies with depth. The state of stress tends to become hydrostatic at great depth. Stress that is uniform in all directions, as beneath a homogeneous fluid, causes dilation rather than distortion in isotropic materials.( A medium whose properties are the same in all directions.) Pore pressures of the interstitial fluids ( oil + water ). In geology, the fluids are generally water, saturating the open pore spaces of a rock column have the same effect as immersing a rock in a water column. The pore pressure (p) is given by: (p) = d’ . g . h

   A significant increasing in pore pressure, which acts in opposite sense of the geostatic pressure, creates conditions to cause gravity deformations. Gravity deformations cause plate movements . Plate movements raise well-field pressures , as evident in records of the 2006 5.9 underwater quake in the Gulf of Mexico.
   E.O.R. techniques are specifically designed to raise pore pressures in the well-fields.

   This how tectonic movements and oil drilling are interdependant on each other. These practices require serious reconsideration.




SOURCE: Wikipedia, E.O.R. page
SOURCE: Salt tectonics , biblioteca
SOURCE: NALCO/TIORCO WEBSITE