Laboratory‐determined permeability of cores from the Kola Superdeep Well, USSR

Abstract

We have conducted constant flow‐rate permeability measurements on three core samples taken from the 12‐km‐deep well on the Kola Peninsula, USSR. All cores are from 11.4– 2.0 km depth. Pore pressures, Pp, used in these permeability measurements ranged from 112–117 MPa. Measurements were performed at effective confining pressures (Peff=pc‐Pp) ranging from 10 to 400 MPa. The resulting permeabilities varied from approximately 2.5 × 10−17 m2 (25 μDa) at a Peff of 10 MPa to 1 × 10−22 m2 (0.1 nDa) at a Peff of 300 MPa. The unusual sensitivity of permeability to Peff exhibited by these samples is most likely the result of severe stress‐relief crack damage that occurred during coring and sample retrieval. This strong pressure dependence underscores the importance of measuring permeability at in situ pressures to obtain meaningful bounds on in situ matrix permeabilities in this well. In an attempt to infer closure pressure of these stress‐relief cracks, and provide estimates of in situ Peff, we have analyzed the pressure dependence of permeability, resistivity and crack porosity. By applying an equivalent‐channel‐model analysis, these data appear consistent with either an in situ pore pressure exceeding the hydrostat by as much as 100 MPa or a hydrostatic Pp and sub‐lithostatic in situ vertical stress. In either case, if this closure pressure accurately reflects the in situ confining pressure, then an upper bound on in situ matrix permeabilities would be 1 × 10−20 to 2 × 10−19 m2 for the samples studied.