Abnormally high formation pressures in petroleum regions of Russia and other countries of the CIS

Statistical analyses of oil and gas pools in ancient platforms (Precambrian), young platforms (post Hercynian), and mobile belts (foreland troughs, and intermontane depressions) of the Commonwealth of Independent States (C.LS.), do not reveal any significant differences in the relationships between commercial production and the magnitude of overpressure. However, pressure data from all three structural provinces indicate 90% of all oil and gas pools are in reservoirs with pressure abnormality coefficients (A(c)-the quotient of the measured pressure divided by the hydrostatic pressure) less than 1.8 (0.81 psi/ft, 18.7 kPa/m), suggestive of a commercially practical upper limit for productive reservoirs. In ancient platforms, more than 90% of hydrocarbon pools are present in reservoirs in which the A, is less than 1.7 (0.77 psi/ft, 17.8 kPa/m). Oil pools in ancient platform provinces are more common in reservoirs where the abnormality coefficient ranges from 1.1-1.3 (0.50-0.54 psi/ft, 11.5-12.4 kPa/m), whereas most gas pools occur in reservoirs with an A, ranging from 1.06-1.1 (0.48-0.50 psi/ft, 11-11.5 kPa/m). Very few oil and gas pools in ancient platforms occur in reservoirs with abnormality coefficients greater than 1.6 (0.72 psi/ft, 16.6 kPa/m). On young platforms, the majority of oil pools occur in reservoirs in which the A, is less than 1.6 (0.72 psi/ft, 16.6 kPa/m). Gas pools in young platforms are found in reservoirs with abnormality coefficients as high as 2.0 (0.9 psi/ft, 20.8 kPa/m). In mobile belt provinces, 90% of oil pools occur in reservoirs with A, values less than 1.8 (0.81 psi/ft, 18.7 kPa/m). A small number of pools occur in reservoirs where the abnormality coefficient is as high as 2.0 (0.9 psi/ft, 20.8 kPa/m). In mobile belt provinces, 90% of all oil and gas pools occur in reservoirs with A, values less than 1.8 (0.81 psi/ft, 18.7 kPa/m) and are most common where the abnormality coefficient ranges from 1.2 to 1.3 (0.54-0.59 psi/ft, 12.4-13.6 kPa/m). The statistical data demonstrate that as the A, increases, the frequency of occurrence of commercial oil and gas accumulations generally decreases. Very few oil and gas pools, regardless of structural setting, occur in reservoirs with abnormality coefficients greater than 1.8 (0.81 psi/ft, 18.7 kPa/m).