Recent studies have shown that enhanced oil recovery will be the focal point for approximately 50% of the global oil production in the upcoming two-three decades. According to the several ballpark studies conducted on EOR techniques, results show that for reservoirs with oil viscosities ranging from 10 to 150 m Pa.s., polymer flooding seems to be an ideal development strategy. However, when the oil viscosities exceed 150 m Pa.s., polymer injectivity and pumping efficiencies can turn out to be major inhibiting factors, thereby limiting the range of oil viscosities for which polymer flooding can be utilized. The core reason for this is that the values of viscosity for the injected water containing polymer, calculated for the beneficial mobility ratio, can lead to the inhibiting factor stated above. Previously conducted lab studies have shown that supramolecular systems are very resistant in high temperature - high salinity systems. To be able to achieve the easier injection, the injected supramolecular viscosity will be kept at lower values and then increased to the levels right before or upon contacting the oil in the reservoir. The core difference between conventional polymer systems and supramolecular polymer systems is that the latter disassemble and re-assemble as opposed to degradation when exposed to extreme shear stress and temperatures. It can therefore be said that supramolecular polymer systems are self-healing in nature. The phenomenon has been observed in cases where polymers with high molecular weight are forced through narrow flow channels. Though molecular division takes place, supramolecular systems have shown a tendency of reassembly later on. Therefore, adaptability of these systems to bounded or restricted environments can be established. This study will add the modeling and simulation components of supramolecular systems which can be effectively utilized in high temperature-high salinity conditions through adjustments to viscosities and interfacial properties of these assemblies. This will help compare the displacement efficiency of supramolecular systems which efficiently perform in a wide range of reservoirs such as thin zones, and reservoirs within permafrost conditions. This can significantly benefit the oil and gas companies worldwide in preparing a technically feasible, but also, a cost effective EOR development strategy, whenever polymer injection is of consideration.
Applicability of electrokinetic effect in improving water injectivity in tight sandstone is studied. DC potential and injection rate are varied for optimization and determination of their individual impact on clay discharge and movement. The liberated clays were characterized through size exclusion microfiltration and ICP-MS analysis. Real time temperature and pH monitoring were also informative. Results showed that severalfold (up to 152%) apparent increase of core permeability could be achieved. Some of the experiments were more efficient in terms of dislodgement of clays and enhanced stimulation which is supported by produced brines analysis with higher concentration of clay element. The results also showed larger quantity of clays in the produced brine in the initial periods of water injection followed by stabilization of differential pressure and electrical current, implying that the stimulation effect stops when the higher voltage gradient and flow rates are no more able to dislodge remaining clays. Additionally, fluid temperature measurement showed an increasing trend with the injection time and direct proportionality with the applied voltage. The basic theory behind this stimulation effect is predicted to be the colloidal movement of pore lining clays that results in widening of pore throats and/or opening new flow paths.
Scale-inhibitor-squeeze lifetime is measured by the duration for which the scale-inhibiting chemical is released at a concentration greater than the required minimum inhibitor concentration (MIC). Hence, enhancing scale-inhibitor adsorption and storage may proportionately enhance squeeze lifetime. With most oilfield squeeze scale inhibitors being aqueous-based, they are unlikely to be adsorbed on an oil-wet formation in optimal quantity. Investigations are made in this research on how to create the appropriate formation condition so that adsorption and lifespan of scale inhibitor in an oilwet carbonate reservoir are enhanced, focusing on preflush design (formation-conditioning stage). Surfactants (of anionic and nonionic type), a cosurfactant, and alkali are deployed and results are evaluated through interfacial tension (IFT), phase-behavior analysis, coreflood studies, and inductively coupled plasma-mass spectroscopy (ICP-MS) analysis. Flow experiments are conducted in simulated reservoir condition by use of data and materials from a high-temperature and high-salinity carbonate reservoir. The results reveal that nonionic surfactant is most favorable in terms of scaleinhibitor-squeeze lifetime, which is enhanced by as much as 240% compared with conventional treatment. It is concluded that through correct preflush design and formation conditioning, scale-inhibitorsqueeze lifetime can be extended significantly.
With the advances in data-driven methods, they have become more widely-used in analysis, predictive modeling, control and optimization of several processes. Yet, as it is a relatively new area in petroleum industry with promising features, the industry overall is still skeptical on use of data-driven methods as it is a data-based solution rather than traditional physics-based solutions. In this sense, in order to shed light on the background and applications in this area, this study comparatively evaluates one of the methods used in waterflood surveillance and optimization called capacitance-resistance model illustrated on two types of mature fields with high and low-perm characteristics. Data-driven methods serve as a robust tool to turn data into knowledge. Historical data generally has not been used in an effective way in analyzing processes due to lack of a well-organized data where there is a huge potential of turning terrabytes of data into knowledge. A capacitance-resistance model is built to identify the well connectivities between the wells and then carry that knowledge to better reservoir management through optimization of injection and production in two different sets of data. In CRM modeling, analysis of injection/production data at associated injectors and producers reveals the connectivities and further optimization leads to optimum injection values. Steps and the methodology of building a CRM model using real data is illustrated to exemplify the whole process in a comparative way between two mature reservoirs. We introduce the concept of application of spatial constraints in terms of injection-producer maximum influence radius to accelerate and improve the solution where knowledge of radius of influence for an injector is known by historical data and experience. The theoretical and practical information is supported with mature field examples to investigate the factors affecting the performance of vertical wells in tight and intermediate-permeability reservoirs along with the outline of the major challenges and how to solve them. This study also illustrates the challenges of application of CRM on a tight reservoir in the order of 0.1md and comparison of the application of the method on a more intermediate-perm reservoir. Field data used in this study is from publicly available, open access source, Division of Oil, Gas & Geothermal Resources (DOGGR) website - http://www.conservation.ca.gov/dog
Hydraulic fracturing is an important method to recover shale oil and gas that has drastically increased U.S. energy production in recent decades. Shales are low permeability formations where natural resources are trapped, and require a well-planned hydraulic fracturing process and a highly developed fracturing (fracking) fluid for efficient oil/gas recovery. In this study, a pH-responsive solution synthesized by supramolecular assembly of maleic acid and an amino-amide in an aqueous media is described as a potential fracking fluid owing to its mobility control, proppant carrying and settling capacities. Previous investigations on this solution system had shown its large potential to replace displacement fluids in EOR due to pH-tunable and reversible viscosity behavior. The main working mechanism is that; the initial viscosity of injected solution is kept at moderate/high values to easily transport proppants and easily inject the fluid; and then decreased when the solution reaches a position near fissures for settling of proppants. It has been reported by rheology tests of the developed fracking fluid, which consists of the supramolecular solution and proppants (silica sand), viscosity can be changed about 1600 times from pH 3.8 to pH 8.3 in a reversible fashion at only 2 wt.% concentration. On the other hand, sedimentation studies indicated that the sedimentation speed of the silica proppants decreased around five orders of magnitude from pH 4 to pH 8, again in a reversible way. Furthermore, experimental studies revealed that the developed supramolecular solutions have both reversible pH-responsive properties, and tolerance against high salinities and elevated temperatures. Another outstanding property of these supramolecular solutions is their self-healing feature which enables them to disassemble and reassemble upon exposure to extreme shear stresses, while polymer viscosifying agents the fracking fluids degrade and break up under similar conditions. The supramolecular assembly system discussed in this study has a promising potential to become next-generation fracking fluids with its outstanding properties including but not limited to pH-sensitivity, reversible viscosity, high proppant transfer capacity, tolerance to high temperatures and salinity, self-healing behavior, environmental friendliness and sustainability.
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