Page 376 - Fundamentals of Gas Shale Reservoirs

356 WETTABILITY OF GAS SHALE RESERVOIRS

20,000 40

18,000 10% leak-o 35
2 2 prop.

16,000 15% leak-o
30
14,000
Imbibed volume (m 3 ) 12,000 3 20 Water loss (%)
30% leak-o
25
3 prop.
10,000
8,000
15
6,000
10
4,000 4 4 prop.
2,000 5
0 0
0 15 30 45 60 75 90 105 120
Time (days)

FIGURE 16.13 Imbibed volume of brine versus the soaking time for the Muskwa shale with different values of fracture aperture.

fracture aperture size increases the imbibed volume rapidly, concentration, (ii) is faster along the depositional lamina-
mainly because fracture–matrix interface increases. tion, and (iii) decreases with increasing the salt concentration.
The data suggest that in addition to capillarity, adsorption
effect of clay minerals and osmotic potential influence water
16.7 INITIAL WATER SATURATION IN uptake of gas shales. Furthermore, in contrast to the intact
GAS SHALES samples, the crushed shale packs imbibe more oil than water.
In a crushed sample, both hydrophobic and hydrophilic
The imbibition experiments reported in this chapter were pores are well connected. Therefore, the observed difference
conducted on dry shale samples while in situ shales may between the oil uptake of crushed and intact samples is
have some initial water saturation. The initial hydration state primarily due to the difference in connectivity of pore net-
can influence the spontaneous imbibition rate in gas/water/ work in crushed and intact samples. In simple, the poorly
rock systems (Li et al., 2006). However, the initial water sat- connected hydrophobic pore network of intact samples
uration of some tight gas (Newsham and Rushing, 2002) and becomes artificially well connected by crushing the samples.
gas shale (Wang and Reed, 2009) reservoirs is abnormally This interpretation is backed by the complete spreading of
low. Such reservoirs are in a state known as “sub‐irreducible oil on fresh breaks of all the shale samples studied here.
initial water saturation,” created by the excessive drying at
high paleo temperatures and pressures, and the lack of
sufficient water for increasing the irreducible water satura- REFERENCES
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Unconventional Resources Conference 2014, 1–3 April, The
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16.8 CONCLUSIONS Agbalaka C, Dandekar AY, Patil SL, Khataniar S, Hemsath JR.
The effect of wettability on oil recovery: a review. Paper pre-
sented at the SPE Asia Pacific Oil and Gas Conference and
The experimental data presented in this chapter demonstrate Exhibition 2008 – “Gas Now: Delivering on Expectations;”
the complexity of liquid flow in gas shales. Although the 2008; Perth, Western Australia, Australia, 1, p 73–85.
studied samples are strongly oil‐wet based on contact angle Agrawal S, Sharma MM. Impact of liquid loading in hydraulic fractures
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the connected pore network, which imbibes a considerable Agrawal S, Sharma M. Impact of liquid loading in hydraulic
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