RIASSUNTO
Mature, high temperature, high salinity oil reservoirs pose significant challenges for chemical enhanced oil recovery (CEOR) and a simple robust solution is missing, yet highly desired, by asset holders.
Viscoelastic surfactants are a class of amphiphilic molecules that can form supramolecular structures or networks such as wormlike micelles or microgels in water, building up high viscosity fluids. These structures are dynamic and shear sensitive so that at high shear conditions of injection into a reservoir they have the viscosity of water, without degradation, and build up viscosity in the reservoir. In addition, they are able to sweep low permeable sections of the reservoir. This hybrid functionality maximizes the areal sweep efficiency and oil mobilization.
Wintershall, in collaboration with BASF, has developed a viscoelastic surfactant with a unique performance profile for CEOR application. Triphenoxymethane (TPM) are highly salt tolerant (tested at 25% TDS with high divalent cation concentration). The dosing is low -depending on the desired viscosity- for example ca. 1000 ppm for 25mPas at 10sec-1 shear in brine at 70oC. Furthermore, it is a single component system which excludes any risk of chromatographic separation in the reservoir. We have shown that they are stable over long periods and non-toxic. Furthermore, we have shown that in coreflood experiments they mobilize significantly more oil than other chemistries and reduce the residual oil saturation by 7%, with maximum oil recovery at less than one pore volume of injected fluid.
We will report on the performance profile: injectivity, retention, oil mobilization relative to other technologies, etc. We will also discuss observed structure activity relationships derived from a combination of molecular modelling and experiment which drives the development of this unique class of compounds. Finally, we will touch on the on-going scale-up for potential field trials in 2014 and 2015.