American Oil and Gas Reporter - February 2018 - 71

SpecialReport: Advancing Shale Science

Fracturing Fluid Entrapment in Capillary Flow Paths

Wetting
Phase

Nonwetting
Phase

Wetting
Phase

Nonwetting
Phase

FIGURE 3

1.0

Partial Relative Permeability Jail Caused by Frac Fluid Entrapment
Gas Phase

Water Phase

0

Complete Picture
Operators need to think about the
complete picture of production operations
to determine the best strategies and procedures for handling and treating water.
That includes ensuring the accountability
of waters to their sources, understanding
where water goes in the reservoir and
what comes out with it, and the quantity
and quality of produced and flowback
water. Figure 4 outlines the basic tasks
of field water handling.
The key issues include the cost of implementing successful water recycling
methods to comply with applicable regulations, determining the total amount of
water that realistically can be treated and
reused, and accurately evaluating treatment,
disposal and reinjection options. This requires high levels of technology, expertise
and training, as well a concerted time commitment to make sure water handling practices are as cost-effective as possible while
reducing potential environmental impacts.
The process should begin with operators
considering a number of practical measures
to better understand the reservoir and recognize potential problems. This necessitates
testing and obtaining preliminary data as
soon as wells are available to "listen" to
the reservoir and figure out what field information is revealing. Different stimulation
strategies, completion designs and production technologies can be tested and
monitored to observe the impacts on hydrocarbon production and water cuts.
The industry is expressing a clear preference for green fracturing fluid chemistries
in shale plays, especially low-toxicity compositions that break down rapidly. For all

FIGURE 2

Relative Permeability (Fraction)

some downhole problems, including a
"relative permeability jail" condition expressed by the reverse funnel effect.
Liquid loading occurs as full trapping
only in hydraulic fractures, but as incomplete or partial trapping in low-permeability natural and induced fractures.
As shown in Figure 2, permeability jail
is caused by hysteresis of drainage following the imbibition of water and capillary forces holding water in narrow pore
throats, restricting gas flow and preventing
the disconnected water from flowing.
Figure 3 illustrates a partial jail condition caused by fracturing fluid entrapment. This condition results in a "hybrid"
relative permeability curve that describes
the incomplete water trapping of natural
fractures, allowing for more gas and water
flow than the full jail curve.

0

Water Saturation (Fraction)

1.0

FIGURE 4
Field Water Handling Tasks
Natural and
Produced Waters

Marketing, Disposal and
Reinjection

Water Handling

Storage and
Transport

Regulations and Policies

FEBRUARY 2018 71
American Oil and Gas Reporter - February 2018

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