An approach to determining pre-drilling formation pore pressure with credibility for deep water exploration wells

Key words:  deep water drilling  formation pore pressure  uncertainty  credibility  probabilistic analysis

Abstract:

For the lack of reference data from offset wells of deep water exploration well drilling，an improved approach to determining overburden pressure gradient was presented and the relationship of time and depth was established. With the probabilistic theory, the influence of each parameter on result and the interrelationship between them of Eaton model were studied. An approach to pore pressure prediction was provided by a combined methodology of Eaton model and effeclive-stress method using interval velocity data, and the pore pressure profile with credibility was established. This pore pressure profile is not a single curve but the interval with credibility information. Higher the credibility or the degree of overpressure, wider the interval of pore pressure gradient and the uncertainty area，otherwise, although narrower the uncertainty area, lower the credibility. The results of a well in West Africa deep water area agree well with ihe field test value.