Vi. Zilberman et al., Prediction of Abnormally High Formation Pressures (AHFP) in petroliferous salt-bearing sections, J PET SCI E, 29(1), 2001, pp. 17-27
Prediction of overpressures [Abnormally High Formation Pressures (AHFP)] in
the evaporite sequences is indeed a challenging problem. Several technique
s are suggested here for the solution of this forecasting problem. For a re
liable AHFP forecast it is necessary to delineate the salt plugs. A method
of accomplishing this is presented here. In many cases there is evidence of
vertical gas migration along flanks of salt plugs and associated fractured
zones (and faults). The composition of gases in the secondary traps in the
sealing evaporite sequence is the same as that of gas in the massive, majo
r accumulation below. Predictive precursors of the AHFP include lithologica
l barrier (e.g., anhydrite) with decreasing drilling rates and appearance o
f "gas clay" in circulating mud (i.e., plastic greenish-gray and brown clay
with gas bubbles). (C) 2001 Elsevier Science B.V. All rights reserved.