Haihua Pei

Improvement of Sweep Efficiency by Alkaline Flooding for Heavy Oil Reservoirs

Severe viscous fingering during water flooding of heavy oil leaves a large amount of oil untouched in the reservoir. Improving sweep efficiency is vital for enhancing heavy oil recovery. This study presented a laboratory study for improving sweep efficiency by alkaline flooding in heavy oil Reservoirs. This included glass-etched micromodel flooding tests, one-dimensional flooding experiments and three-dimensional physical model study. The micromodel tests show that W/O droplet flow plays a prominent role in the alkaline flooding to improve sweep efficiency. There is a minimum alkaline concentration that generates the W/O droplet flow, and the W/O droplet flow is more obvious with the alkaline concentration increasing. A series of flood tests were conducted using 325 mPa · s, 2000 mPa · s, and 3950 mPa · s heavy oils to assess the effectiveness of W/O droplet flow in alkaline flooding for enhanced heavy oil recovery. The flood tests results demonstrate the considerable potential for improved heavy oil recovery by alkaline flooding, and moreover, the incremental oil recovery has been found to increase as the alkaline concentration increases. The result obtained in three-dimensional physical model study indicates that the sweep area can be greatly improved by the formation of W/O droplet flow in alkaline flooding.

The Effect of Oil Viscosity, Permeability, and Residual Oil Saturation on the Performance of Alkaline Flooding in the Recovery of Heavy Oil

Abstract This article examines the effect of oil viscosity, permeability, and residual oil saturation on the performance of alkaline flooding to enhance heavy oil recovery. The results show that the in situ generated water-in-oil emulsion during alkaline flooding can effectively improve sweep efficiency and, consequently, improve heavy oil recovery. The tertiary oil recovery can reach over 20% of the initial oil in place using 1.0% NaOH. The incremental oil recovery of alkaline flooding increases with the residual oil saturation. However, the tertiary oil recovery gradually increases with decreasing the permeability. But the effectiveness of alkaline flooding does not decrease with the increasing oil viscosity.

Study on Influencing Factors of Chemical Flooding for Heavy Oil

Alkali and alkali/surfactant displacing agents are designed for two kinds of heavy oil. Results of emulsifying capacity, dynamic interfacial tension (IFT) and water-wet core flooding tests show that, although alkaline/surfactant systems exhibit better capacity in emulsification and IFT reduction, oil recovery values of alkaline/surfactant flooding are lower than those of alkaline flooding. Glass-etched micromodel tests further demonstrate that, when alkaline solution penetrates into the oil phase, water streams break into ganglia coating oil film. Water ganglia may be entrapped by narrow throats, consequently presenting a water-oil alternating slug flow. Similar water ganglia also appears in alkaline/surfactant flooding, however, water channeling along the pore surface occurs subsequently, resulting in its relatively lower oil recovery.

Laboratory Investigation of Enhanced Heavy Oil Recovery by Foam Flooding with Low Gas–Liquid Ratio

Abstract This article presents the results of a laboratory study of foam flooding with low gas–liquid ratio for heavy oil in Shengli oilfield. Foam flooding tests were performed in cores, sandpacks, and using a 3D physical model to study the factors affecting displacement efficiency such as gas–liquid ratio, injection slug size, and the viscosity of crude oil. The results showed that the tertiary oil recovery of polymer-enhanced foam flooding with a gas–liquid ratio of 0.2:1 could reach 39% for heavy oil with a viscosity of 325 mPa · s at 55°C, which was 11% higher than alkali/surfactant/polymer flooding by injecting 0.3 pore volume of the same chemical slug. However, the tertiary oil recovery decreased with increasing viscosity of the crude oil.

Experimental study of self-aggregating proppants: New approaches to proppant flowback control

Due to the high rate of proppant flowback after hydraulic fracturing stimulations, surface modified quartz sand proppants with excellent proppant flowback control abilities, self-aggregating proppants, were prepared. These surface modified proppants can aggregate together spontaneously and form a proppant column in water based liquid environment. Analyses show that the strong hydrogen bonds contribute to the absorption of the surface modifier onto the proppants, and the softening effect of the water to the polymer coating prompts the connection between the proppants. Scanning electron microscope pictures show that proppant particles are stacked together tightly. The stable structure contributes to the macroscopic stability of the proppant column. The maximum sand free flow rate of the model packed with modified proppants is 2.8 times larger than that of untreated proppants by average, indicating that the self-aggregating proppants exhibit excellent proppant flowback control abilities. In addition, fines control tests show that the modified proppants can also prevent the migration of the formation fines effectively, reducing the conductivity loss caused by particle migrations. By virtue of the reaggreating property and the encapsulation action of polymer coating to the crushed fragments, the fracture conductivities are increased by 3 times even at large closure stresses. The results provide a new alternative for proppant flowback control while do little damage to the permeability of the proppant pack.