Page 284 - Fundamentals of Enhanced Oil and Gas Recovery

272 Mohammad Ali Ahmadi

Figure 9.5 Continent-wise breakdown of risked in-place and technically recoverable shale oil [2];
*SA represents South America, **NA stands for North America (here excludes the USA). EIA [6].

the tight reservoirs reported in the literature including thermal maturity 0.6%–1.3%,
porosity less than 10%, total organic carbon higher than 1%, and the API gravity
higher than 40 [1,9]. Fig. 9.6 depicts the range of permeability for both conventional
and unconventional oil/gas reservoirs.
It should be mentioned the definition of tight oil and shale oil reservoirs is differ-
ent; to avoid any misunderstanding we should describe both terminologies. In techni-
cal speaking, the term of shale oil is used for reservoirs like mud shale rocks and
source rocks; however, the term of tight oil reservoir is used in cases including low
permeable carbonates, silty sandstones, and sandstones [1,10].

9.2 SHALE OIL AND OIL SHALE

In technical speaking, we do have two different terminologies that may cause a
misunderstanding; these two terms are shale oil and oil shale. Oil shale defined as a
rock comprises a solid organic materials called Kerogen; Kerogen is a compound of
fossilized organic material. In other words, the rock containing the kerogen is not
necessarily shale; apparently Kerogen is not a real crude oil. The terminology of shale
oil is employed in case of trapping of oil in a very tight formation, for example, per-
meability is around 0.001 mD, the fluid cannot straightforwardly flow into the pro-
duction well; hydraulic fracturing is employed to accelerate the fluency of the flow,