Taking the North Saertu Development Area (NSDA), La-Sa-Xing oilfield in Daqing, China as an example, this paper presents best practices to improve mature field waterflood recovery. Placed onstream in 1963, development of the multi-layer sandstone reservoir experienced three-round infill drillings, EOR polymer flood and ASP flood. Strong reservoir heterogeneities, producing at water-cut >90% starting in 1999, various IOR/EOR activities and several well-pattern types overlapping vertically led to extreme challenges for further improving waterflood recovery. This paper first introduces the general reservoir geology, reservoir heterogeneity characteristics, fluid properties and reservoir conditions, followed by illustrating its 60-year development history and key IOR/EOR activities implemented. The focus of this paper is to illustrate the strategy, fit-for-purpose technologies, and effective reservoir management practices to further improve waterflood recovery at extra-high water-cut development stage.

The discussed improved recovery practices are based on deliberate reservoir characterization and remaining oil study by integrating wireline logging, 3D seismic, production logging, sealed core data, production performance data and various other performance monitoring data. Several pilots on water-controlling, producing by-passed thick pay sands as well as re-arranging individual well pattern were conducted, providing a basis for field-wide application. Key strategy and technologies adopted are: 1) subdivision of individual injection-production interval and reduction well spacing; 2) improving water injection at individual well pattern and single flow-unit level; 3) combining waterflood and polymer/ASP flood by utilizing the same wellbore or well pattern to develop marginal pay sands in a cost-effective way; 4) improved zonal water injection by reducing individual injection thickness and permeability contrast within the injection interval; 5) improved injection profile through profile modification; 6) integrated approach to mitigate injected water channeling in thick pay sand; 7) cyclic water injection; 8) well drilling along fault plane producing by-passed oil; and 9) horizontal wells producing poorly swept or attic oil. The IOR and reservoir management activities have successfully arrested production decline, mitigated water-cut rising, leading to an increased waterflood recovery by >2.5%.

Mainly implemented at development stage with extra-high water cut of 92%-95%, the integrated IOR and reservoir management activities discussed in this paper are all feasible, proved technically successful and cost-effective. These practices provide a road map and solutions for extending oilfield life or rejuvenation of a waterflood mature oilfield.