Suspended solid (SS) particles in the produced water of X2M ASP flooding project were separated by membrane filtration and identified to consist mainly of alkali earth metal carbonates and silica precipitates. A compound formulation of chelatants was developed to stabilize the water phase of ASP flooding produced fluid and prevent or reduce precipitation of both alkali earth metal carbonates and silica. The compound chelatant was put into a limited field trial in the surface production system of X2M ASP flooding project to evaluate its effects on the quality of treated produced water. The averages SS content of treated ASP flooding produced water was decreased to below the 20ppm SS specification limit for re-injection by a dosage of chelatant at 480ppm or above. Scale removal performance of the compound chelatant was also observed during the field trial.

1. Introduction

Alkaline-surfactant-polymer (ASP) flooding has been proven to be a promising recovery method to extract large volume of oil remaining in the ground after conventional oil recovery methods have been implemented. The incremental oil recovery efficiencies of 11 completed ASP flooding field tests ranged from 19 to 34 % of OOIP[1, 2]. ASP flooding is now considered to play an important role in improving the oil recovery and ultimately extending the life of numerous mature reservoirs throughout the world. However, ASP flooding is still facing some major obstacles in produced fluid handling on its way to commercial application. While significant decrease of water-cut of produced liquid and increase of oil production have been achieved, ASP flooding has resulted in tremendous increase of suspended solid (SS) particles in produced fluid, causing great troubles in produced water treatment and re-injection, as well as scale deposition in tubing and surface production facilities[3, 4]. The state-of-art produced water treatment processes such as gravity settling, electrocoagulation, IAF, DAF, biological treatment and bed filtration were not effective enough for the removal of some of the tiny particulate contaminants in the produced water of X2M ASP flooding project. Chemical coagulation and flocculation of ASP flooding produced water was found to be unacceptable due to extremely high dosage, high expense, and disposal of huge amount of toxic sludge[5, 6]. It is thus necessary to search for new treatment methods for ASP flooding produced water based on the sources and characteristics of SS in the troublesome produced water.

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