Abstract

Over the last years SCAL, Inc. performed many thousands of desorption isotherms and we noticed that even in shale oil plays, in the oil window, the source rock is gas bearing. Thermal maturity alone cannot explain these findings.

While the thermal maturity starts and maintain the hydrocarbon generation is the compaction and associated molecular sieving that controls the final output of this hydrocarbon generation both quality and quantity. The generation can be slowed down almost stopped by compaction.

The compaction and thermal maturity combined can explain very well why the shale source rock is gas bearing even in shale oil plays in the oil window. The oil saturation measured in the shale source is unfortunately laboratory generated from the unconverted kerogen.

This model will explain why the gas content is higher in shale oil plays rather than mature shale gas reservoirs.

The proposed compaction model can also explain the current time hydrocarbon generation we observed both in the reservoirs and in the laboratory. The current time reservoir hydrocarbon generation can be a significant in some reservoirs.

Some of the problems associated with crushed rock analysis such as laboratory generated porosity, laboratory generated adsorption, laboratory generated oil saturations are discussed in detail and better evaluation techniques are proposed. These new techniques are based on a strict material balance of the sorption and desorption isotherm experiments performed on native state shale samples (not crushed).

The shale plays need to be evaluated using a source and reservoir rock approach in order to reconcile the commercial hydrocarbon rates observed in the producing wells. The matrix permeability obtained by the GRI method on crushed samples is several orders of magnitude too low and can only justify oil productions in the nanobbl/day range.

Practical fluorescence observations can be used to find the gradual transition from source to reservoir rock. Cost effective oil permeability tests are proposed to identify zones of suspected of oil production. The shale reservoir rock can be analyzed using conventional core analysis techniques.

Our automated gas desorption measurements are the best direct method available to identify ‘real time’ the high maturity zones and at the same time provide data for accurate gas reserve calculations. These measurements also provide a way to calibrate our slightly crushed tight rock analysis making it harder to produce highly questionable laboratory results.