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Abstract

Two highly successful polymer pilot experiments were carried out between 1987 and 1993 on the Daqing oil field (People Republic of China) after favorable laboratory results and preliminary reservoir studies.

The Daqing oil field is a fluvio-deltaic formation with several sand beds and great heterogeneities. The oil is slightly viscous (9.5 cp), water is fresh and the temperature is 45 C., making the conditions favorable for polymer injection.

Each pilot consisted of 4 injectors and 9 producers. One pilot was devoted to one reservoir, whereas simultaneous injection into two reservoirs was performed in the second pilot.

Polymer injection was started in 1990 with a 915-ppm-solution of polyacrylamide. Approximately 0.6 PV of solution was injected in each pilot, yielding a significant decrease in the water-cut and a respective oil production of 73 120 m3 and 118 950 m3 in April 1993.

The results of the pilots were matched with a numerical simulator and interpreted in terms of reservoir description. The injection parameters were optimized in terms of viscosity and slug size, in order to extend the process to the whole field.

The sensitivity of the process to the reservoir heterogeneity was also considered.

Introduction

The field of Daqing, discovered in 1959, is the largest oil field in the People Republic of China, with Original Oil In Place exceeding two billions tons. The field is located 1 000 km north of Beijing, in Heilongjian province, in an area corresponding to a continental sedimentary basin. The structure is a 145 km-long, 10 km-wide and 700 to 1 200 m-deep antic line trending N-NE/S5W There are three reservoirs (Goataizi, not developed as yet; Putuaohua, referred to as the P reservoir and Saertu, referred to as the S reservoir) with a very complex structure. Sandbodies of various sizes corresponding to channel deposits with poor lateral extension or to sheet sands with very good continuity are interbedded with shales.

Water injection was started very early in order to maintain the pressure. Since 1979 production has been maintained at one million barrels per day thanks to an intensive campaign of infill drilling. More than 10 000 wells in a line-drive pattern have been drilled so far. The viscosity of the oil (9.5 cp) and the degree of heterogeneity of the reservoir have resulted in moderate displacement efficiency and a high water-cut in the production. EOR techniques were considered as early as 1984 in order to increase recovery and to prevent the decline of oil production.

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