Page 283 - Fundamentals of Enhanced Oil and Gas Recovery

Enhanced Oil Recovery (EOR) in Shale Oil Reservoirs 271

Figure 9.4 The map of assessments in terms of shale reserves across the world [2]. http://www.eia.
gov/analysis/studies/worldshalegas/.

Fig. 9.5 depicts the portion of the shale oil in place and technically recoverable
shale oil, individually. The graphs have been developed utilizing data reported by
energy information administration (EIA) [6]. As clear be seen from these charts,
Europe has the highest shale oil in place and producable shale oil reserves; conversely,
Australia is the last in this ranking [2,6].
The main production method for producing shale oil from their tight reservoirs is
using hydraulic fracturing in the horizontal wells. This method facilitate the oil pro-
duction due to the reservoir depletion; however, the achievable recovery factor of
such method in most of the cases is lower than 10% [7]. For instance, Clark [8] used
different approaches to figure out the value of the shale oil recovery factor; according
to the results the most probable recovery factor is almost 7%. This means that huge
volume of oil remained in the shale oil reservoir and this will be a motivating force to
innovate new technology to enhance production from such type of reservoirs [1].
The main and general rock property of tight and shale reservoir is drastically low
permeability in comparison with other types of the oil/gas formations. For instance,
the value of permeability in shale reservoirs varies from 0.001 to 0.0001 mD [9];
however, this value in most of the conventional oil/gas formations is 10000 times
higher than that of the value in the shale and tight reservoirs. Practically speaking, in
several rare cases the shale reservoir does have some micro-fractures that resulting in
improvement of the effective permeability; in these cases the value of the effective
permeability is much higher than that ot the shale matrix permeability without frac-
tures. In addition to the permeability characterization, different common properties of