A novel core analysis techniques described which provides detailed characterization of both gaseous and 1iquid phase hydrocarbons saturating petroleum reservoir rock. The method is suitable for the delineation of oil-water contacts, gas-oil transition zones and the passage of miscible flood fronts. Fresh full diameter core is subsampled from the radial center to minimize the impact of mud filtrate invasion and other mechanisms which alter the natural fluid distribution. Subsamples are preserved in serum vials capped with impermeable septa. The vials are heated to establish elevated equilibrium partial pressures of hydrocarbons in the gaseous phase surrounding the sample. The septum is punctured allowing hot gases to be injected onto a wide bore capillary gas chromatography column. Hydrocarbons from C1 to C30 are separated and quantified using a linear temperature program and flame ionization detection. Interpretation of analytical results is facilitated by the core hydrocarbon log which contains plots of bath total hydrocarbon content and the relative distribution of major hydrocarbon classes versus depth, using standard wireline lagging scales. The utility of the technique is demonstrated in the analysis of care from a fractured reservoir shale.
Characterization of in situ fluids in petroleum reservoir rack is essential for optimal delineation and exploitation of hydrocarbon resources. Surprisingly little progress has been made in this area of petroleum technology over the past forty years. The primary source of information remains the evaluation of borehole resistivity lags. This technique relies heavily an the empirical equations of Archie (1) which relate borehole resistivity. formation water salinity and porosity to interstitial water saturation, using a suite of constant parameters whose values may be determined in the laboratory, derived from other well logs, or estimated from past experience in a given horizon. Hydrocarbon volumes are inferred as the difference between pore volume and formation brine volume. In clean sandstones and carbonates the Archie equations as modified by Winsauer et al. (2) or Wyllie and Gregory (3) are commonly used. The resistivity treatment has been extended to shaly sands by Hill and Milburn (4). Waxman and Smits (5) and Clavier et a1. (6), using cation exchange capacity data to compensate for the presence of conducting solids. Well bore data is, in general, as good as the quality of the input parameters to the Archie equations, but is inherently limited by the depth resolution of the resistivity tool and the empirical nature of the analytical equations. Even within zones at relatively homogeneous lithology, rock properties among individual samples may vary widely from the average values used in log interpretation (1, 7–9)
Core analysis techniques using atmospheric pressure retorting or Dean-Stark extraction/distillation methodology (IO) can provide reliable estimates of the bulk fluid content of core specimens. However, core analysis fluid saturations often vary dramatically from in situ values due to the operation of a variety of alteration mechanisms consequent to coring and transport to the laboratory for analysis.
