Abstract: Comparison of Seal Capacity Determinations in Conventional Cores with Cuttings

Robert M. Sneider, John W. Neasham, George W. Bolger

Comparison of field hydrocarbon column heights (HCH) with HCHs estimated from mercury/air capillary pressure curves of conventional cores demonstrate good agreements in many of the 300 North American reservoirs studied. Comparison of HCHs estimate from seals of conventional cores with cuttings from the same interval suggest that mercury/air capillary pressure measurements of cuttings can be extremely useful to estimate seal capacity.

Where top and lateral seals are the result of lithology we see a good-to-excellent relationship between the column height of hydrocarbons trapped and the hydrocarbon column height (HCH) calculated from mercury capillary pressure curves of vertical plugs cut across the seal bedding. The plugs are sealed with epoxy so that mercury can enter only from the top and bottom. The mercury/ air capillary pressure curves are run using a system that can inject mercury at pressures up to 60,000 psi (equivalent to a hydrocarbon column of over 5000 ft for 35° API gravity oil).

Depending upon seal type and nature of the lithologic interbedding, high pressure mercury injection curves (HPMIC) for cuttings can approximate those from core. Injection pressures for cuttings are usually lower than equivalent cores for a particular percent pore volume occupied. Empirical adjustment factors (EAF), expressed in psi, are derived from comparisons of HPMIC measurements on couplets of cores and "simulated cuttings" or real cuttings of the same seal interval. The EAF values are applied to determine entry pressures when cuttings are used alone. The EAF factors vary from a low of 15-20 psi (air/mercury) for "A" type seals to approximately 250 psi for "D" type seals at 5 percent pore volume saturation.

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