Abstract

The paper focused on developing foamed polymer system for profile modification and modeling the process in laboratory. Experimental results show that foamed polymer solution can sharply increase the flowing resistance of displacing fluid in high permeability or thief layers and greatly modify the injection profile. It is safe, efficient and economical modifier for the wells that need large volume of modifier injection.

The stability of in-situ formed foams was tested in sandpacks. Under proper temperature and pressure condition, a relatively low concentration polymer solution can suspend enough foams for profile modification. At the temperature of 60 °C and pressure of 30 Mpa, the lowest polymer concentration is 1500 mg/l. The flowing resistance of the foamed polymer solution is 30 to several hundred times higher than that of traditional polymer solution with the same concentration. This property is useful in alleviating the fingering effect in polymer flooding process or modifying the water injection profile.

The profile modification experiments were carried out in two parallel sandpacks with a permeability ratio of 5:1. At the later stage of waterflooding, when the water cut of the high permeability sandpack increases to 95%, only 20% oil has been produced in low permeability one, and the ratio of water got by them is more than 15:1. After the profile modification treatment by foamed polymer solution, the profile became uniform and the recovery of the low permeability sandpack increased to that of high permeability one.

Introduction

This paper introduce the concept of using foamed polymer solution for water injection profile modification in water flooding reservoir. Foamed polymer solutions of this study were intended for application as conformance treatments for the purpose of providing better mobility control and improved sweep efficiency in conventional polymer flooding.

Conventional foams are used to control and improve the injection profile in secondary or tertiary gas-injection process and reduce gas mobility.) The applications of conventional foams in petroleum industry also include steam-foam, CO2 foam, foamed drilling muds and foam fracturing fluids. From early 70s, researchers began to develop a technique to improve the stability of oil-recovery foams by adding a thickening agent such as polymer in aqueous phase. There is a detail review about researches in this field in R. D. Sydansk's paper2. 1993, R. D. Sydansk reported his work on the developing and using of polymer-enhanced foam (PEF) for oil-recovery applications in naturally fractured reservoirs2,3. In his work, high permeable sandpacks were employed as fracture channels. Different from conventional foams or PEFs, gas phase in foamed polymer solution was produced in-situ after the injection, not added or generated in the ground prior to injection, and the foam quality is relatively low.

Profile modification is the main production operation during high water cut period for waterflooding reservoirs. One widely used modifier is polymer gel system; the other is fine particle system. The former is prohibitive due to the high prices of polymer and agents, and is not environment friendly. Its influence distance is restricted by gelling time and economic factors. The latter has the potential disadvantage of damaging low permeability formations.

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