Page 46 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

30 Gas Wettability of Reservoir Rock Surfaces with Porous Media

2.4.4 Effects of Surface Surfaces Caused by Different
Roughness on Gas Liquids 80
Wettability 77 References 82
2.4.5 Wetting Situation of Gas- Further Reading 84
wetting Rock Sample

At present, gas wettability is evaluated by traditional evaluation techniques
that are used to measure liquid wettability. However, discussions are needed
urgently on whether the frequently used quantitative evaluation method for
liquid wettability can be applicable for evaluating gas wettability due to its
low viscosity and strong compressibility. Furthermore, traditional methods for
assessing wettability are limited in their applicability and have certain limita-
tions in the oil/water/solid system. Therefore it is necessary to summarize tra-
ditional wettability evaluation methods to discuss their feasibility for
evaluating gas wettability.

2.1 TRADITIONAL WETTABILITY EVALUATION
METHODS

There are numerous mature methods for assessing wettability [1].Quantitative
evaluation methods mainly include contact angle, Amott method, and US
Bureau of Mines (USBM) method; and qualitative evaluationmethods include
imbibition rates, microscopic examination, flotation, glass slide method, relative
permeability curves, capillary pressure curves, capillarimetric method, displace-
ment capillary pressure, permeability/saturation relationships, and reservoir
logs. Additionally, NMR-Relaxation and dye adsorption are suitable for evaluat-
ing fractional wettability.

2.1.1 Contact Angle
Contact angle mainly applies to assessing wettability of pure liquid (there is
no other interaction between solid/liquid) and a horizontal, smooth, homo-
genic, and massive solid system. It is also used to determine the wetting degree
of reservoir rocks. Wettability is determined by the angle θ between tangent
line from the crossing point of three phases—gas, liquid, and solid—to the
surface of water drop and the interface of solid and liquid. When θ , 90
degrees, water selectively wets the rock surface, and the rock is called water-
wet. The smaller the θ is, the more a rock is considered to be strongly water-
wet. When θ . 90 degrees, oil selectively wets the rock surface, and the rock is
called oil-wet. The larger the θ is, the more a rock is considered to be strongly
oil-wet. When θ 5 90 degrees, the wetting capability of oil phase and water
phase are equal. The rock surface is considered to be neither water-wet nor oil-
wet, but intermediate-wet. Moreover, the wettability of powdery solid particles
can be measured using the Washburn method. Contact angle measurement is
a simple technique that is easy to implement and obtain quick results.