In this article, we present the synthesis and characterization of water‐soluble polymers with hydrophobic moieties. The polymers were synthesized in aqueous solutions utilizing β‐cyclodextrins as solubility enhancers to bring the hydrophobic monomers into solution. Polymers were made with different spacing between polymer backbone and phenyl moiety by using styrene, allylbenzene, and 4‐phenyl‐1‐butene as hydrophobic moieties, respectively. The effect of the presence of CDs during synthesis as well as this difference in spacing was investigated by rebinding free β‐CDs to the polymers. The interactions between polymers and CDs were studied by ITC and this revealed some differences between the polymers. Polymers made in the presence of CDs showed a markedly stronger binding to free CDs. The same was observed with polymers with a longer spacing between backbone and phenyl moiety. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 6619–6629, 2009

Interactions between methyl tert-butyl ether (MTBE) and water have been investigated by scanning calorimetry, isothermal titration calorimetry, densitometry, IR-spectroscopy, and gas chromatography. The solubilization of MTBE in water at 25 °C at infinite dilution has ΔH° = -17.0 ± 0.6 kJ mol(-1); ΔS° = -80 ± 2 J mol(-1) K(-1); ΔC(p) = +332 ± 15 J mol(-1) K(-1); ΔV° = -18 ± 2 cm(3) mol(-1). The signs of these thermodynamic functions are consistent with hydrophobic interactions. The occurrence of hydrophobic interaction is further substantiated as IR absorption spectra of MTBE-water mixtures show that MTBE strengthens the hydrogen bond network of water. Solubilization of MTBE in water is exothermic whereas solubilization of water in MTBE is endothermic with ΔH° = +5.3 ± 0.6 kJ mol(-1). The negative mixing volume is explained by a large negative contribution due to size differences between water and MTBE and by a positive contribution due to changes in the water structure around MTBE. Henry's law constants, K(H), were determined from vapor pressure measurements of mixtures equilibrated at different temperatures. A van't Hoff analysis of K(H) gave ΔH(H)° = 50 ± 1 kJ mol(-1) and ΔS(H)° = 166 ± 5 J mol(-1) K(-1) for the solution to gas transfer. MTBE is excluded from the ice phase water upon freezing MTBE-water mixtures.

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Short-circuit connections between injectors and producers resulting from induced or natural fractures in tight chalk reservoirs can divert the injection water resulting in poor sweep efficiency and early water breakthrough in producers. The overall impact is a significant reduction in oil recovery. Curing of these connections can be achieved through the application of a chemical conformance treatment aimed at plugging off the fracture and shutting the connected zone. Knowing the volume of the fracture is essential for such a conformance treatment, since it determines the amount of conformance chemical that should be injected. If too little material is pumped, the fracture will not be effectively closed, and if too much material is pumped, there is a risk of contaminating the connected well. However, the fracture volume estimation can be challenging due to the uncertainty of the fracture geometry. Deuterium tracers offer a simple, quick and environmentally friendly method to estimate the volume of the fracture. The method was successfully employed on an injector/producer pair with a known fracture connection in the Danish North Sea. A deuterium tracer was selectively injected at a constant rate via coil tubing (CT) into the connected zone in the injector, and the producer was sampled from the wellhead. With the exception of the fracture volume, all other volumes (and therefore transit times) within the deuterium tracer injection path are known. Based on the deuterium's arrival time, the fracture transit time and therefore volume can be calculated. The use of heavy water (D2O) as a chemical tracer allows DTI to conduct the tracer operation with real-time offshore analysis of the tracer breakthrough. The results obtained were subsequently applied to adjust the injection time and volume of the cement during the operation to cement the fracture.

Long horizontal wells are hydraulically fractured or acid stimulated to economically develop chalk reservoirs in the North Sea. To separate the zones and ensure conformance, each fracture or zone is separated by isolation packers and flow is controlled with a sliding sleeve. With time, conformance control capability of the lower completion may be lost if the sliding sleeve is stuck open or holes are eroded or corroded in the lower tubing. If a shortcut has developed between an injector and producer, either during stimulation or operation of the well, the consequence of losing conformance capability of the lower completion is more severe. Another scenario with serious consequences occurs when the well has been hydraulically fractured with proppant and the proppant is back-produced without a possibility to close off the zone. To mechanically fix this conformance issue, it would require working over the well and replacing the lower completion. In an old (30-40 years) well, this is a challenge. A better solution is to solve the problem chemically by consolidating the sand in the fracture or plugging the fracture connecting the injector and producer. Recovery from the reservoir will then be optimized and the solution is likely to be cheaper than working over the well. Enzymatic CaCO3 technology is a novel chemical system that can be used for plugging fractures and consolidates sand in propped fractures in horizontal wells. All chemicals used offshore in the North Sea need to be compliant with OSPAR regulations; the Enzymatic CaCO3 system is classified as environment-friendly. It also has predictable chemistry and is completely reversible. This paper discusses the process of maturing the technology from concept to readiness for field implementation covering lab testing, IP protection, chemical procurement strategies, environmental impact evaluation, and quality assurance process during field application.