Enhancing the Oil Recovery from Naturally Fractured Reservoirs Using Viscoelastic Surfactant (VES) Flooding: A Field-Scale Simulation.

ABSTRACT

A viscoelastic surfactant (VES) has the combined properties of a surfactant and a polymer. Injection of VES fluids into naturally fractured reservoirs (NFRs) can control the mobility of the injected fluid and enhance the total oil recovery. This paper presents a field-scale simulation to evaluate the performance of a noble VES fluid in enhancing the oil recovery from a naturally fractured reservoir. In this work, the results of coreflooding, computerized tomography (CT)-scan, rheology, interfacial tension (IFT), and adsorption measurements were used to build and calibrate a lab-scale model. Thereafter, a chemical enhanced oil recovery (EOR) modeling simulator developed by a computer modeling group (CMG-STARS) was used to build a field-scale simulation. Real seismic data, permeability and porosity distributions, and operating conditions were utilized to develop and evaluate the simulation model. The results show that VES can outperform the surfactant-polymer (SP) flooding and waterflooding in NFRs; VES improved the oil recovery by 10% and reduced the water cut by 47%, at the same conditions. VES reduced the IFT by two orders of magnitude (100 times) compared to waterflooding. Also, VES altered the rock wettability to a more water-wet status, leading to reduce the relative permeability to water (K rw) by a factor of 10, on average. Finally, the simulation study indicated that applying waterflooding after VES flooding leads to a minor increase in the oil recovery. Overall, this study provides a detailed comparison between VES flooding, SP flooding, and conventional waterflooding in NFRs. Sensitivity analysis was performed to study the impact of treatment parameters on the oil recovery from naturally fractured reservoirs. Using actual NFR data, the optimum VES flooding was determined, which will help in conducting VES flooding for real EOR operations.