Improved Oil Recovery - Product To Process
Authors: Mack James C. 
Published: December 2007

Oil recovery projects designed to improve volumetric sweep have evolved in the past ten years from strictly product applications to the use of advanced process technology. The paper relates this development process technology. The paper relates this development by exploring laboratory work and field-wide projects. The results show that the process approach is a major step forward.

Unsuccessful waterfloods are usually due to either an extreme permeability variation and/or an adverse mobility ratio. The use of polymers in injection water has helped to correct these problems and improved waterflood oil recovery. Laboratory core work has shown that residual resistance factors of 6.0 can be obtained with injection of anionic polyacrylamide. Field-wide projects (product polyacrylamide. Field-wide projects (product approach) have recovered from 0.5 to 3.0 additional bbl of oil per lb of anionic polymer used. Process technology (cationic polymer plus anionic polymer and in-situ gelling techniques) has increased residual resistance factors 6 to 11 times and has pushed the range of incremental oil recoveries to 3 to 16 additional bbl of oil per lb of anionic polymer used.

Better technology, coupled with increased oil prices, has made processes to increase volumetric prices, has made processes to increase volumetric sweep an attractive investment. Criteria for selecting reservoirs for the processes is reviewed.

Introduction

In the past 15 years considerable work has been done on the development of polymers to decrease water mobility, thereby increasing the oil recovery for both secondary and tertiary recovery projects. Polymers reduce water mobility in 2 ways: 1) increasing Polymers reduce water mobility in 2 ways: 1) increasing the viscosity of the displacing slug, and 2) building resistance to the flow of water — making the reservoir more uniform to fluid flow.

This paper examines polyacrylamide laboratory work and field projects designed to decrease water mobility in waterflood operations. The objective on such projects is to improve ultimate oil recovery and make the waterflood more efficient. Efficiency means less produced water handling and less overall water recycling. Although the paper limits discussion to improved waterflooding, the process approach can also be used in micellar and CO2 flooding to insure maximum volumetric sweep and prevent premature chemical breakthrough.

Initial work with polyacrylamides was limited to the study of only the polymer product (anionic polyacrylamide). Extensive core work has been done polyacrylamide). Extensive core work has been done to define the benefits gained by using anionic polyacrylamides. Field projects have been operated polyacrylamides. Field projects have been operated successfully with slugs of straight polymer. In the early 1970's processes were introduced combining other chemicals with the anionic polyacrylamide to improve effectiveness. Development of the cationic polyacrylamide made possible the "CAT-AN" (trade mark) Process polyacrylamide made possible the "CAT-AN" (trade mark) Process where injecting cationic polymer before anionic gives greater residual resistance factors. In 1974 technology was introduced using trivalent metal ions to gel anionic polymer "in-situ". Process technology has proved to greatly reduce water mobility and increase cost performance. The paper reviews the history of polymer flooding from product application on through to the use of current process technology. Improved oil recovery and cost performance benefits are stressed.

PRODUCT APPLICATION AND RESULTS PRODUCT APPLICATION AND RESULTS Development of the use of polyacrylamides in waterflood operations began in the research laboratory. Table 1 shows results of laboratory flood pot tests with an anionic polyacrylamide. The general test procedure was to manifold 4 core samples with procedure was to manifold 4 core samples with varying permeability in parallel. A single injection fluid was pumped into the manifold and allowed to flow simultaneously through all of the samples. Inlet manifold pressure and output flow from each sample were measured.

The samples were exposed from an oil-bearing sandstone. They were dry but contained some dead oil. Samples were resaturated under vacuum with brine prior to the tests. The cores were radial, 3 1/2 in. in diameter with 1/2 in. center hole and about 3 in. long. Flow of the brine and polymer solution was from the outside periphery into the center hole.