Page 19 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff gas injection in oil reservoirs 9

2.3 Experimental methods
In shale and tight cores, it is very difficult to do experiments, as the
flow rate is very low, significant experimental errors can be resulted. In
this section, several experimental setups are discussed.

2.3.1 Core saturation with oil
When an experiment is conducted, the core needs to be saturated with oil. A
conventional process using a desiccator cannot be used, as the core perme-
ability is too low, and the saturation pressure must be high. An experimental
setup schematically shown in Fig. 2.1 may be used. The core is first vac-
uumed for 1 day, for example. The measured dry core weight is W dry .
Then oil is pumped through another pump until a desired high pressure
in the container is reached. Stop pumping oil. Oil will gradually imbibe
into the core because the oil pressure is high, and the core was vacuumed
earlier and the pressure inside the core is low. Gradually, the pressure inside
the core is increased until it reaches the oil pressure in the container. During
the saturation period, the oil pump may be restarted, when the oil pressure
inside the container is dropped owing to oil imbibition into the core. When
the pressure inside the container no longer decreases, the core is almost fully
saturated with oil. Then take the saturated core and measure its weight, W sat .
As is understood, oil cannot enter very narrow pores below some pressure.
As the saturation pressure is higher, oil can enter narrower pores. What pres-
sure should be used? Generally, the saturation should be several hundred psi

Figure 2.1 Schematic to saturate a core with oil.