Summary
The effect of surface-active chemicals on oil/water interfacial tension
(IFT) and wettability in crude oil/brine-rock systems at reservoir conditions
is important in enhanced oil recovery (EOR) processes. However, most of the
experimental studies on IFT and contact angles have been conducted at ambient
conditions and using stock tank crude oils. In this study, live, and stock-tank
crude oils have been used at reservoir conditions to make IFT and dynamic
contact angle measurements using the drop shape analysis (DSA) and dual-drop
dual-crystal (DDDC) techniques, respectively. Yates reservoir rock and fluids,
and two types of surfactants (nonionic and anionic) in varying concentrations
have been used at reservoir conditions of 82°F and 700 psi (27.8°C and 4.8
MPa).
The dynamic oil/water IFT was found to be a strong function of oil
composition, temperature, and showed a slight dependence on pressure. An
attempt has been made to explain the dynamic behavior of IFT using a four stage
mechanistic model involving induction, diffusion, kinetic barrier, and
equilibrium stages. The significant difference observed between the advancing
contact angles of live oil (55°) and stock-tank oil (154°) clearly indicates
the need to use live oils at reservoir conditions to determine in-situ
reservoir wettability. Anionic surfactant altered the weakly water-wet behavior
of live oil to strongly oil-wet (165°). It was also able to alter the strong
oil-wet behavior of stock tank oil to less oil-wet (<135°). The nonionic
surfactant was able to alter the water-wet live oil system to intermediate-wet
(82°), while it did not affect the strongly oil-wet behavior of stock tank oil
system.
The oil-wet behavior observed for live oil using surfactants indicates the
possibility that these surfactants develop continuous oil-wet paths for
potential mixed wettability development. Thus, this study is of practical
significance in cases where the surfactant-induced wettability alterations to
either intermediate-wet or mixed-wet can result in improved oil recovery
through the lowering of both capillary and adhesion forces.
Introduction
The addition of surfactants to the injection water can lower oil/water IFT
and alter the wettability of the rock/oil/brine system and, hence, improve oil
recovery. However, these interfacial rock/fluid interactions are sensitive to
temperature and pressure, in addition to being time dependent. Therefore, the
results of the laboratory tests conducted at ambient conditions cannot be
representative of rock/fluid interactions at real reservoir conditions. Hence,
the experimental study of time-dependent (dynamic) behavior of interfacial
properties (IFT and contact angles) at reservoir conditions (high temperature
and high pressures) is necessary for selection and applicability of suitable
surfactants for economic field application. Also, the selection of a particular
laboratory measurement technique to suit the complex experimental environment
is essential for reliable results at high pressures and temperatures.
Therefore, a brief review of literature on various available measurement
techniques for the interfacial properties of IFT and contact angles as well as
the pressure and temperature effects on these interfacial properties is
provided below.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
12 June 2006
- Meeting paper published:
9 October 2005
- Revised manuscript received:
18 March 2007
- Manuscript approved:
16 May 2007
- Version of record:
25 February 2008
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