Abstract

As the second largest oilfield in China, Shengli oilfield has been one of the largest oil-bearing regions performing polymer flooding in the world. However, varieties of reservoirs and complex reservoir conditions in part of blocks have been the obstacle in performing polymer flooding. At the same time, those blocks where polymer flooding has been conducted are facing the problem of how to improve oil recovery further.

Laboratory experiment and field performance of enhanced foam flooding pilot are described in this paper. The enhanced foam flooding involves a complex system consisting of polymer, foam agent and nitrogen gas, which has a larger value in apparent viscosity. Comparing with polymer flooding, enhanced foam flooding has a better capability in profile control and oil flooding in improving oil recovery.

Laboratory experiments indicate that the flow resistance for enhanced foam in porous media is much larger than that when each of its components flows individually. Pressure gradients have a uniform distribution, which can avoid end-side blocking.

Enhanced foam flooding conducted at Chengdong block is the first well group test in Shengli oilfied. The test consists of four injection wells, three central production wells and nine edge production wells. Field test performance shows that the enhanced foam flooding improves the injection profile of reservoir and increases injection pressure. Therefore, preliminary water decreasing and oil increasing are achieved. The total water cut for well group has decreased from 95.9% before the test to current 88.6%. And daily oil production has been improved from 4.5t to 22.6t. Therefore, besides of polymer flooding, enhanced foam flooding is expected to be a new industrial method to improve oil recovery in Shengli oilfield.

Introduction

Several major oilfields in eastern China have entered the mid and late period of development, so it becomes very urgent for these old oilfields to enhance oil recovery. Foam flooding is a kind of tertiary recovery which uses foam as oil displacement medium, due to high apparent viscosity, strong ability of profile control and selectivity for oil/water blocking. It can improve the fluid apparent viscosity, increase the sweep area, and has strong ability of blocking and profile control, so it can be used successfully in the oilfields.1, 2 Foam is a kind of pseudo-plastic fluid which has special migration law in porous media.3 According to the reservoir characteristics of Shengli oilfield, enhanced foam flooding has been carried out, and a complicated multi-component system consisting of polymer, foam agent and nitrogen gas has been injected in the reservoir. In this paper, Chengdong oilfield is selected for discussion. Laboratory experiment and field performance of enhanced foam flooding pilot are described in this paper. They show that the enhanced foam flooding is a very effective tertiary oil recovery method and has good commerical prospect in the Shengli oilfield.

Experimental Description
Experimental Devices and Materials

According to different experimental purposes, we use two types of displacement devices: core displacement device and long slim tube displacement device.

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