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Abstract

Information relative to the preparation of two polymer flood pilots in the West Central Saertu area of the giant Daqing oil field in China is presented. The reservoir features of the West Central area of the field contribute to suggest polymer injection as an attractive process. Numerical simulations as well as economical calculations based on anticipated optimum operational conditions have confirmed this interest. The primary scope of the reported laboratory study is the use of a new methodology for selecting the most appropriate polymer chemical structure. Three maim selection criteria, namely maximum intrinsic viscosity, minimum adsorption and absence of attractive polymer-polymer interactions were considered and a polyacrylamide containing 20% of acrylate group was chosen. This polymer was found to show high effective viscosity and low retention in core flows. A xanthan sample also suitable according to these technical criteria was not considered due to economical reasons.

The two pilot tests are being designed on these bases. The first one aims at checking the ability of polymers to reduce vertical channeling within a single layer. The second will evaluate the improvement of vertical sweep efficiency when two separate layers open in wells with single completions are subjected simultaneously to polymer injection. The well layout of each pilot and the type of information expected from the observation wells are described.

Introduction

The Daqing oil field is located in the Songliao basin in the Northeast part of China (Heilongjang province). There are seven structures in the field, but only the northernmost Lamadian structure has an original gas cap. This oil field has three producing formations: Saertu, Putaohua, and Gaotaizi. They are between 700 and 1200 m (2,295 and 3,934 ft) deep. The Daqing oil field was discovered in 1959. In June 1960, a 20-km2 (8-sq mile) waterflood pilot test unit was established in the central part of the field. On the basis of pilot test results, the field has been developed sequentially since 1962. By 1976 the annual output had reached 58 × 106 m3 (336 millions bbl), as established by the development program. Currently, the field is in a high-water-cut stage of development, but the annual output has been maintained above 50 × 106 m3 In order to maintain as long as possible this high production level, many techniques have been used. Among them, EOR is being investigated. The Saertu and Putaohua formation reservoir features in the West Central area of the field suggest polymer injection as an attractive process. Two pilot tests are being designed to check this interest. The present paper describes their preparation, which has involved extensive laboratory work, reservoir numerical simulations, and the main characteristics of the two planned pilot tests.

II. RESERVOIR DESCRIPTION AND PAST HISTORY

II.1. Geology and Reservoir Characteristics West Central area is located in the central part of the main structure of Daqing field (Fig. 1). This area is typical of the flooded deltaic plain where fluviatile sand bodies have been deposited during Putaohua and Saertu ages (in continuity with older Gaotaizi formation). A typical vertical cross-section of Putaohua formation is shown in Fig. 2. It indicates clearly a variable lateral extension of sandbody deposits interbedded with clays (and/or shales). Two main types of sand bodies may be easily differentiated:

  • first type corresponds to channel deposits it is generally identified as a fining upwards sedimentological sequence.

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