Page 214 - Gas Wettability of Reservoir Rock Surfaces with Porous Media

198 Gas Wettability of Reservoir Rock Surfaces with Porous Media

Table 6.1 Correlation of Surface Tension

Sample Surface Tension (25 C) (mN/m)
0.4% ABS 33.85
0.4% ABSN 33.25
0.4% OP-10 30.65
0.4% TWEEN80 35.15
0.4% SPAN80 25.67
0.4% polymeric alcohol SYP-1 56.93
0.4% FCS-08 18.40

below 60 C and the pH value was adjusted to neutral. Stirring was discontin-

ued when the emulsion cooled to below 50 C. The liquid was then filtered

and poured out, and the emulsion was prepared with a fluoropolymer drilling
fluid additive, FCS-08.

6.1.2.3 EVALUATING FCS-08 PERFORMANCE
6.1.2.3.1 Surface Tension and Interfacial Tension
Surfactant-based water-block resistance agents frequently used for drilling
fluids, including ABS, ABSN, OP-10, TWEEN80 and SPAN80, and polymeric
alcohol water-block resistance agent SYP-1, frequently used for acid/fracturing
fluids, were chosen. The surface tension of these water-block resistance agents
and FCS-08 at 0.4% concentration were measured, respectively. The measure-
ment results are shown in Table 6.2.
It can be seen from Table 6.1 that at the same concentration (0.4%), poly-
meric alcohol SYP-1 reduces the surface tension of water solution the least.
The surfactants ABS, ABSN, SPAN80, OP-10, and TWEEN80 reduce the surface
tension of water solution up to 40 mN/m, with SPAN80 being the best among
all evaluated samples. FCS-08 exhibited the best effects in reducing surface
tension, which was within 20 mN/m.
Based on Young-Laplace’s equation, P c 5 2σ cos θ=r,the decrease in inter-
facial tension σ between gas and water (surface tension of water phase)
can greatly reduce the capillary pressure, and further reduce the possibil-
ity of water-blocks. It thus follows that water-block resistance agent
FCS-08 can reduce the rate of damage of low-pore and low-permeability
reservoirs by water-block, by decreasing the surface tension of filtrates in
drilling fluids.
The higher the oil and water interfacial tension, the lower the reservoir
permeability and more severe the degree of water-block damage. The
interfacial tension of water solutions (ABSN and FCS-08 with concentra-
tion of 0.1% 0.5%) and oil was measured. The results are as shown in
Table 6.2.