RESUMEN
Bulk foam analysis (static test) is simple and fast, which makes it a cost-effective method for screening and ranking hundreds of surfactants being considered for foam applications. Coreflood tests (dynamic test) can also be used, but it is quite laborious and costly. However, previous reports show that ranking based on static tests sometimes differs from ranking based on dynamic tests. To date, the reason for such a discrepancy is not well understood. Some believe that it may be due to faulty experimental design while some others believe that there is no discrepancy if the right foam performance indices are used to describe and compare the results from both methods. For the first time, this study reports a systematic series of static tests conducted on different foaming solutions (with surfactant concentration ranging from 0.025 to 5 wt%) and duplicated in dynamic tests using the same core sample for all the surfactant solutions. The dynamic test was also repeated on three different rocks of a wide permeability range (26-5000 mD) for each of the surfactant solutions. Unlike previous studies, here multiple dynamic foam indices (limiting capillary pressure, apparent viscosity, trapped foam, and trapped to mobile foam ratio) were measured and compared with the performance indices measured from the static tests (foam texture and foam half-life). Dynamic tests were in total agreement with static tests for all the foam formulations. However, it was observed that the pore size of the base filter disk used in the static foam analyzer can be a potential source of conflicting results when comparing with dynamic test. This is because a threshold pore size exists above which some foam properties (apparent viscosity and trapped foam) significantly decreased compared to the properties before that threshold. Foam limiting capillary pressure is the only foam property that does not show such a trend. It also appears that such threshold occurs above a certain surfactant concentration (0.025 wt%). Apparently, it becomes imperative that the pore size of the filter disk used in the static test and the porous medium used in dynamic tests must be on the same side of the threshold point, otherwise there may be disparity in their results. The threshold surfactant concentration should also be determined. The role of these two factors (pore size and surfactant concentration) requires further investigation.
RESUMEN
This paper investigates the phase behavior and mutual interactions between a light crude oil and CO2 at high pressures and high temperatures (HPHT). To do so, we have measured PVT properties of the CO2-oil system at HPHT using a PVT setup. We have also tried to present a detailed methodology for measuring PVT properties of CO2-oil systems and highlight the difficulties such as oil vaporization by CO2 during the experiments. A crude oil sample, collected from a Malaysian oil field, was used here. Our experiments indicated that, CO2 solubility in the oil increased at higher pressures when measured at a fixed temperature. Our experiments also showed that increasing the test temperature would reduce CO2 solubility in the oil, while its effect is more significant at higher pressures. The swelling factor (SF) measurements showed an increasing trend with pressure up to a certain value so-called extraction pressure, at which, the SF started to be reduced even became less than one. The measurements of oil viscosity indicated that CO2 dissolution in the oil sample could reduce the mixture viscosity up to 61%. The interfacial tensions between CO2 and the crude oil at different pressures were also measured while the results were used to estimate the minimum miscibility pressure (MMP) and the first contact miscibility (FCM) pressure. The IFT measurements at various pressures displayed a reduction trend as a result of more CO2 dissolution in the oil but with two different slopes. That is, at lower pressure values, the measured IFTs were sharply reduced with pressure, while the reduction rate of the IFT became less when pressures exceeded the extraction pressure. This study helps with determining the optimum pressure and temperature conditions of CO2-oil systems to have a minimum IFT, a maximum CO2 solubility and SF, and a minimum oil viscosity that are favorable for CO2-enhanced oil recovery projects. Additionally, the methodology presented here gives guidelines on how to design PVT experiments of CO2-oil systems for petroleum and chemical engineering applications.
