--> Seal Capacity Measurements and Description of Mudrocks from the Gulf of Mexico, by R. D. Shew, S. H. Tennant, A. S. Kornacki, and D. R. Rollins; #90986 (1994).

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Abstract: Seal Capacity Measurements and Description of Mudrocks from the Gulf of Mexico

Roger D. Shew, S. H. Tennant, A. S. Kornacki, D. R. Rollins

The evaluation of the sealing potential of non-reservoir facies should be conducted at both core and field scales. The core scale evaluation involves the direct measurement of seal capacity of a particular lithotype, while the determination of effective seals at the field scale involves analysis of hydrocarbon occurrences in associated reservoirs inferred from fluid levels and formation pressures. In this paper, we describe seal capacity measurements performed on representative mudrock samples from several discoveries in the deepwater Gulf of Mexico.

Non-reservoir lithologies in these discoveries are dominantly marls, foram-bearing claystones, claystones, and mudstones. Claystones (Tet-ep facies) contain <1/3 silt; mudstones (Tet facies) contain 1/3 to 2/3 silt size particles. Stressed permeabilities of these samples are in the nanno-darcy range. Thinly laminated intervals composed of siltstone/mudstone couplets also occur in many fields; these represent waning phase turbidite deposition. The silts are commonly hydrocarbon-bearing even though apparently separated by nanno-darcy mudstones. Petrographic, XRD, SEM, Cat Scan, PFID, grain size, and petrophysical analyses have been used to describe these samples.

Seal capacity measurements have been performed on both unstressed (Autopore: Hg/Air) and stressed samples. In the stressed cell (I-Sw), brine permeability is initially measured and then Soltrol (a refined oil) is used to measure capillary properties. Comparisons between the techniques may be made by using conversion factors that account for differences in fluid properties (interfacial tension and contact angles). Entry pressures between 380 and 1000 psi (brine/soltrol system) have been measured on mudstone and claystone samples indicating that these lithofacies are theoretically capable of holding significant hydrocarbon columns.

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