New and Effective Foam Flooding To Recover Oil in Heterogeneous Reservoir
Authors: Zhang Yunxiang , Yue Xiangan , Dong Jianxia , Yu Liu 
Published: December 2007

Abstract
It is well-known that in oil and gas fields development process, foam is widely used as mobility control agent or blocking agent to displace oil and gas, block gas channels and fractures or high permeability layers etc. However, higher oil recovery efficiency is undoubtedly a top-priority factor for managers to decide whether foam flooding can be adopted. According to laboratory percolation and oil displacement experiments, this paper presented a new method of using foam as a displacing agent to recover oil in heterogeneous reservoir. Unlike other foam flooding methods, this work based on the mechanism of both lowering interfacial tensions to a super-low value (10-3mN/m grade) and improving sweep efficiency of displacing fluid. The foam preformed by co-injecting natural gas and a kind of three-component combined solution has a greater blocking effect in high permeability layer of heterogeneous physical model. The percolation result showed that the diversion of fluid from high permeability layer into medium and low permeability layers apparently depends on the flowing resistance in high permeability layer; the diversion ability of foam is far greater than that of polymer.
The oil displacement experiments showed that, for this foam composition, the final oil recovery factor can be improved nearly 30% initial reserves over waterflood recovery factor for model whose permeability variation coefficient is 0.72, nearly one and half times than that of alkaline-surfactant-polymer system. This paper modeled the field injecting project of foam flooding in Daqing oil field and got a good match result. Besides, this paper put forward some measures of improving foam flooding effect.

Introduction
Generally speaking, the waterflood efficiency of heterogeneous reservoir is relatively lower. In order to promote the production of hydrocarbons, one often injects displacement fluids into subterranean hydrocarbon-bearing formations to improve the final oil recovery factor of oilfield. Various gases and more complex fluids, such as alkaline solutions, polymer solutions, surfactant solutions, alkaline-surfactant-polymer (ASP) solutions and foams, are widely used as displacement fluids in both miscible and immiscible oil displacement floods.
Since Fried first put forward foam flooding method in 1961, foams are receiving increasing attention in the oil industry. The merits of foams lie in that foams have some advantageous characteristics, notably as excellent blocking effect and distinguished mobility control effect in enhanced recovery operations. Although foams were first utilized to block fractures, to prevent gas channeling and gas override during gas flood (or steam flood), they have now been applied in many new technique fields with the development of investigations on foam system, oil displacement mechanism and flowing behavior etc. For example, strong and super-strong foam was used to plug fractures or high permeability streaks, the foam provided a considerable reduction in chemical costs relative to gels without significantly reducing the effectiveness of the conformance improvement treatment (CIT)[1]. In addition, some viscofying foams were used as mobility control agents to efficiently sweep oil from a subterranean oil-bearing formation and particularly from oil-bearing fractures containing gravity-segregated oil or from oil-bearing fractures in fluid communication with an aquifer.
In general, the CIT and related plugging treatment are static applications of the foam, in that the foam remains substantially stationary in the formaion once it is placed therein. The mobility control process is a dynamic application of the foam, in that the foam moves across the formation in correspondence with a flood front. According to the concept of foam, a foam is commonly defined as a composition comprising a gas phase dispersed throughout a surrounding medium, such as a liquid. In this definition, the term "surrounding medium" can be either one single composition or a multi-composition. As such, foams have been used in a number of roles according to their different fluid components.