Scaling of Low-Interfacial-Tension Imbibition in Oil-Wet Carbonates

Abstract

Summary Primary and secondary oil recovery from naturally fractured oil-wet carbonate reservoirs is very low. Enhanced oil recovery (EOR) from these reservoirs by use of surfactants to alter the wettability and reduce the interfacial tension (IFT) has been extensively studied for many years, but there are still many questions regarding the process mechanisms, surfactant selection and testing, experimental design, and, most importantly, how to scale up the laboratory results to the field. Therefore, the primary objective of this study was to determine the effect of scale on the oil recovery from cores with different dimensions under low-IFT conditions. There was a particular need to perform experiments by use of cores with larger horizontal dimensions because nearly all previous experiments have been performed in cores with a small diameter, typically 3.8 cm. We adapted and modified the experimental method used for traditional static-imbibition experiments by flushing out fluids surrounding the cores periodically to better estimate the oil recovery, including the produced emulsion. We used microemulsion-phase-behavior tests to develop surfactant formulations used in this study. These surfactants gave ultralow IFT at optimum salinity and good aqueous stability. Although we used ultralow-IFT (approximately 0.002 dynes/cm) formulations for most of the experiments, we also performed tests at low IFT (approximately 0.3 dynes/cm) for comparison. A second major objective of this study was to develop a simple analytical model to predict the oil recovery as a function of vertical- and horizontal-fracture spacing, rock properties, and fluid properties. The model and experimental data were found to be in good agreement considering the many simplifications made to derive the model. The scaling implied by the model is significantly different from the traditional scaling groups in the literature. The model is useful for both interpreting the experiments and for scaling the results from the laboratory to the field.

A new surfactant wettability alteration model for reservoir simulators

“…Injector wells to the left and right of the core and a producer well at the top of the container flow at a rate of 0.5 pore volumes per week to recover the produced fluids and maintain the test solution concentration in the container. This flushing rate is approximately that used by Li et al (2017).…”

“…The produced oil can be more difficult to quantify if the surfactant solution forms emulsions. Li et al (2017) used modified static imbibition cells where the produced emulsions were periodically displaced from the cell with fresh surfactant solution and the emulsions were separated to better quantify the oil recovery. They systematically evaluated different chemical formulations and core dimensions to better understand the process mechanisms and how to scale up the experimental results from the lab to the field using an improved scaleup group.…”

“…Figure 6b shows the average oil concentration in the core after 40 days versus height. Reduction of IFT allows imbibition driven by buoyancy (gravity) forces to produce a conical shape in 3D (Li et al, 2017;Tagavifar et al, 2019).…”

Mechanism of Improving Water Flooding Using the Nanofluid Permeation Flooding System for Tight Reservoirs in Jilin Oilfield

“…Generally, the reservoirs with an average permeability of >0.3 mD can be developed by water flooding, but their ultimate recovery factor is less than 10%. In recent few years, many researchers have been working actively on the ways to improve water flooding, such as surfactant injection and nanofluid injection. − Previous research studies indicated that the oil displacement efficiency depends mainly on the imbibition effect generated by capillary force during water flooding of the tight reservoir. , However, the existing surfactants are mostly micron-sized, making them fail to efficiently enter the pores and throats of the tight reservoir matrix. Thus, the field injection–production relationship fails to be built, resulting in serious imbalance of injection and production.…”

Role of Emulsification and Interfacial Tension of a Surfactant for Oil Film Displacement

“…Since then, numerous efforts have been devoted to further reduce the IFT between oil and water. Current technologies enable very low IFTs (10 –1 –10 –2 mN/m) or even ultralow IFTs (≤10 –3 mN/m). − In some cases, however, the performance is still below expectation, even if an ultralow IFT is reached. At present, another voice in academia is stating that emulsification should be considered as the major function of surfactant flooding.…”