Performance Evaluation And Mechanism Analysis Of HPAM Solution With Broad-distribution Relative Molecular Mass
Authors: Lu Xiangguo , Liu Huanjun , Wang Shuxia , Wang Xiaoyan 
Published: March 2015

Broad distribution relative molecular weight HPAM ("B-HPAM" for short) was produced by mixing with three kinds of different HPAM at different weight ratios, whose viscosity-average molecular weight were 19×106, 25×106, 35×106, respectively. During the chemical flooding stage, the small flow resistance in high permeability formation led the HPAM solution to flow through easily. Firstly the larger polymer clews absorbed in the larger pore throat and then the smaller clews absorbed in the smaller pore throat. Enlarged the swept volume and enhanced oil recovery. Therefore, it was a promising profile control method.

A series of experiments were carried out to study the performance characteristics and mechanisms of "B-HPAM" by dynamic light scattering (DLS), gel permeation chromatography (GPC), Brookfield viscometer, rheometer, and core flooding system. Besides, there was a successful pilot test in No.1 Oil Plant of Daqing Oilfield in April 2005.

The results showed that the distribution of the relative molecular weight had a little effect on the hydraulic diameter (Dh) of polymer molecule. But it influenced the distribution of the hydraulic diameter. The broader the distribution of the relative molecular weight, the broader the distribution of the hydraulic diameter (Dh). There was little difference in viscosity, shearing resistance, temperature resistance and visco-elasticity between "B-HPAM" and "N- HPAM" ("narrow distribution HPAM").

The core flooding tests indicated that the broader the distribution of the molecular weight, the broader the Dh distribution, which led to a decrease in inaccessible pore volume (IPV), an enlarging in swept volume, and an increase of adsorption capacity. Eventually, the resistance factor and residual resistance factor increased.

Furthermore, according to the pilot test in Daqing Oilfield, the stage recovery percent of "B-HPAM" was 8.37% higher than that of "N-HPAM" (6.28%), which presented outstanding profile modification as well as oil displacement effect. Moreover, there had already been a great effect on enhancing oil recovery and decreasing water cut.

Introduction

Currently, most of the domestic oilfields experienced ultra-high water cut and the task of stabilizing oil production and controlling water production was very difficult. It was more and more difficult to discovery new oilfields in the short run. Therefore, it's the inevitable choice for the petroleum industry in China to tap the potentials of domestic old oilfields. For the developed old oilfields in China, the polymer flooding must be carried out due to serious heterogeneity and poor water flooding effect (Huo. 2002; Yang and Cheng. 2004). In recent years, major breakthroughs were made in chemical flooding technology and its application in Daqing Oilfield.

The incremental oil production of polymer flooding was more than 1000×104t for five years in a row (Wang et al. 2001; Wang et al. 1999). With large-scale field applications of polymer flooding, the remaining reservoir which was suitable for polymer flooding was of low permeability and serious heterogeneity. Therefore, the sweep efficiency decreased and the recovery efficiency reduced due to the poor compatibility of polymer and reservoir rock. Therefore, there was an urgent need to develop a new polymer of better performance or improve the performance of polymer to satisfy the demands of oilfield development.