ABSTRACT

Usual geological and geophysical methods frequently fail to show that reservoir beds are discontinuous. This is due primarily to the lack of control or the lack of data resolution. When this situation occurs one or more elements of a hydrocarbon-bearing trap will be invisible to the explorationist. It maybe possible, however, to take the available data and demonstrate that there is reservoir separation using an approach based on petrophysical parameters. Salinity trapping was proposed as an exploration technique, Jones (1959) and was used in the Rocky Mountain Area. Meteoric water enters the outcrop mixing basinward with the in situ formation waters. Trapping conditions preserve the in situ water causing high salinity anomalies which sometimes coincide with a hydrocarbon accumulation. In many basins, however, reservoir rocks do not outcrop yet there are significant differences in the salinity of formation waters. The differences in salinity definitely demonstrate reservoir separation. Shales from different source areas may have different clay mineral suites. The different mineral suites are sometimes manifested on well logs as a difference in shale conductivity. Reservoir separation between sandstones is demonstrated if the seemingly correlative sandstones are encased in shales with different conductivity. Subtle petrophysical parameters can allow the explorationist to demonstrate reservoir separation and the existence of a potential hydrocarbon-bearing trap where the usual exploration methods fail.

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