Abstract: Evaluating Seal Facies Permeability & Fluid Content from DST Data

Hugh W. Reid

The value of knowing the permeability of a seal facies is to establish which are the "leakiest" barriers, hence the most dubious traps to downgrade in exploration follow up strategy.

One advantage of using a DST to compute these permeabilities is that in numerous cases a minor quantity of hydrocarbon is produced in tight seal facies tests and so the permeability found is the permeability effective to the hydrocarbon phase. Since it is the potential for leakage of hydrocarbons that is of interest, not leakage of the water phase, the tight hydrocarbon tests provide the most direct tool for this assessment.

Once the permeability effective to the hydrocarbon phase is known, a range of possible displacement pressure can be estimated from empirical correlations. From these values in turn the approximate trap holding capacity may be estimated for the non leaky barriers.

Useful information may often be extracted from even the tightest tests.

For example, the presence of residual, non producible hydrocarbons in the silty barrier facies, updip from reservoir pinchouts, may be detected from "mud recovery DSTs", even if no oil or gas was produced on test.

The hydrocarbon presence may be inferred from the configuration of the shut in pressure curve and other subtle indications.

These will be demonstrated with examples. Such information may aid hydrocarbon strategy for if a leaky seal is known to contain residual oil, this may warrant moving updip to find the reservoir.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994