Novel CO2/N2 Foam Concept and Optimization Scheme for Improving CO2-foam EOR Process

Nitrogen and Carbon dioxide are the most common gases utilized in enhanced oil recovery (EOR) techniques. Most of the gas injection process suffers from the gravity override and viscous fingering resulting in lower oil recovery. Foam is introduced in enhanced oil recovery (EOR) to mitigate these problems encountered during gas flooding. When it comes to the CO2-gas injection the CO2-becomes supercritical at a typical reservoir condition giving it difficulty to form CO2-foam at reservoir condition. The CO2-foam has a common problem to become weaker above its supercritical conditions of 1100 psi and 31°C. As a result, the advantages of using CO2 foam are diminished due to the weakness of CO2-foam at supercritical conditions and results in a lower recovery. However, CO2-foam can be generated by replacing a portion of CO2 with N2 gas. It lacks the understating of mixture properties and its effect on EOR. This study evaluates the performance of CO2/N2 foam at supercritical conditions for EOR. It aims to improve recovery under supercritical conditions by using N2/CO2 mixture foam and optimize the foam quality and CO2/N2 ratio. The results from the experiments showed that the CO2/N2 foam flooding recovered an additional oil of Original Initial Oil in Place (OIIP) indicating that foam flooding succeeded in producing more oil than pure CO2-foam injection processes. Also, the results of foam flooding at different foam quality and CO2/N2 ratio significantly affected the performance and recovery of the process. Hence it is necessary to optimize the CO2/N2 foam parameters flooding process which is affected by the parameters such as foam quality and CO2/N2 ratio. The study also shows an experimental approach for optimizing CO2/N2 foam parameters. The concept of adding N2 to CO2 is a novel way of generating CO2 foam at supercritical conditions. Although investigators are trying different ways to generate the strong and stable CO2- foam, adding N2 to CO2 can be considered to be the easiest way for foam generation as CO2 is always having some impurities in the form of other gases and N2 can be considered as one of such gas helps in generating the foam.

Directional motion of the foam carrying oils driven by the magnetic field

Foams are substances widely used the foam flooding technology, which aim to greatly improve the residual oil recovery. In the present study, we perform a comprehensive investigation on the oil removal process driven by the foam embedded with magnetic particles, under the action of the magnetic force. The experiment shows that the addition of magnetic particles has little effect on the stability of the foam. During the motion of the foam, its maximum displacement and maximum acceleration are fully explored. Such factors as the volume of the foam, the volume of the oil droplet, the mass concentration of magnetic particles, and the Young’s contact angle of surfactant on solid are surveyed in detail. The function curves of the maximum displacement and the maximum acceleration with respect to these variables are obtained in the experiment, and the selection of some optimal parameters is advised. Moreover, the dimensional analysis has been conducted and several scaling laws are given, which are in agreement with the experimental results. These findings are beneficial to understand the oil displacement with the aid of magnetic field, which also provide some inspirations on drug delivery, robots and micro-fluidics.

Local Equilibrium Mechanistic Simulation of CO2-Foam Flooding

Mechanistic modeling of the non-Newtonian CO2-foam flow in porous media is a challenging task that is computationally expensive due to abrupt gas mobility changes. The objective of this paper is to present a local equilibrium (LE) CO2-foam mechanistic model, which could alleviate some of the computational cost, and its implementation in the Matlab Reservoir Simulation Tool (MRST). Interweaving the LE-foam model into MRST enables users quick prototyping and testing of new ideas and/or mechanistic expressions. We use MRST, the open source tool available from SINTEF, to implement our LE-foam model. The model utilizes MRST automatic differentiation capability to compute the fluxes as well as the saturations of the aqueous and the gaseous phases at each Newton iteration. These computed variables and fluxes are then fed into the LE-foam model that estimates the bubble density (number of bubbles per unit volume of gas) in each grid block. Finally, the estimated bubble density at each grid block is used to readjust the gaseous phase mobility until convergence is achieved. Unlike the full-physics model, the LE-foam model does not add a population balance equation for the flowing bubbles. The developed LE-foam model, therefore, does not add much computational cost to solving a black oil system of equations as it uses the information from each Newton iteration to adjust the gas mobility. Our model is able to match experimental transient foam flooding results from the literature. The chosen flowing foam fraction (Xf) formula dictates to a large extent the behavior of the solution. An appropriate formula for Xf needs to be chosen such that our simulations are more predictive. The work described in this paper could help in prototyping various ideas about generation and coalescence of bubbles as well as any other correlations used in any population balance model. The chosen model can then be used to predict foam flow and estimate economic value of any foam pilot project.

Sweep Improvement Options for Highly Heterogeneous Reservoirs with High Temperature and Ultra-High Salinity: A Case Study in Tarim Basin, China

How to control excessive water production in high-temperature and high-salinity reservoirs has always been a challenge, which has been facing many oil reservoirs in Tarim Basin (China), such as Y2 reservoir with an average temperature of 107 ℃, salinity of 213900 mg/L (Ca2++Mg2+>11300mg/L), and permeability from 2 to 2048 mD. In this work, we present experimental studies to determine the potential EOR process for Y2 reservoir from foam flooding, polymer gel/foam flooding, and microgel/surfactant flooding. To simulate the permeability heterogeneity of Y2 reservoir, a 2-D sand-pack model was used for flooding experiments. Vertically, three layers (first 0.6cm, second 0.8cm and third 1.6cm from top to bottom, respectively) were packed with different size sand to simulate permeability heterogeneity (permeability increases from first to third layer). A 0.3 cm higher permeability zone was also filled inside third layer. Horizontally, permeability gradually decreases from middle to two sides. In this model, injection well was vertical, and production well was horizontal. The effect of impermeable interlayer was also studied by isolating the second and third layer. The results show that conformance treatments using in-situ crosslinked gel or micro-gel are necessary before foam or surfactant injection under a high permeability heterogeneity. When an impermeable interlayer existed between the second and third layer, the additional oil recovery of N2 foam flooding, in-situ crosslinked gel/N2 foam flooding, and microgel/surfactant flooding was 16.34%, 20.37%, 17.50%, respectively, which was much higher than that without impermeable interlayer (9.84%, 13.62%, 12.07%). This implies that when multiple layers exist, crossflow between layers is unfavorable for improving oil recovery, which should be paid extra attention in EOR process. Foam flooding has not only a good mobility control capacity but also a good oil displacement ability (verified by visual observations of washed sand after experiments), which, together with the strong conformance control ability of crosslinked gel, makes in-situ crosslinked gel/N2 foam flooding yield the highest displacement efficiency. Generally, for high-temperature and ultra-high-salinity reservoirs with strong heterogeneity like Y2 reservoir, in-situ crosslinked gel/foam flooding can be a good candidate for EOR. This work provides a potential EOR method with high efficiency, i.e. in-situ crosslinked gel assisted N2 foam flooding, for the development of similar reservoirs like Y2 with high temperature, ultra-high salinity, high heterogeneity and multiple layers. Moreover, this work also highlights that, despite that foam has the ability of mobility and profile control, a conformance treatment is necessary to block high permeability zone before foam injection when the reservoirs has a strong heterogeneity.