Analysis of Factors Influencing Overflow in Changqing Advanced Water Injection Areas

Abstract

Changqing Oilfield is a typical "three-low" (low permeability, low pressure, low productivity) unconventional reservoir. Advanced water injection development leads to abnormal reconstruction of reservoir pressure, forming a narrow density safety window, which results in frequent overflow and great difficulty in disposal. To accurately identify the core targets for overflow prevention and control, this study focuses on "numerical model solving". First, the rheological law of drilling fluid is determined through experiments (providing input parameters for the model), and then a coupled numerical model of water invasion-annular pressure is established. By solving with finite difference discretization, the influences and coupling mechanisms of key factors such as reservoir open thickness, permeability, drilling fluid density, and displacement on overflow are systematically analyzed: the smaller the drilling fluid density, the slower the growth of water invasion flow rate; the larger the reservoir open thickness and the higher the permeability, the greater the water invasion flow rate; when the drilling fluid displacement increases, migration acceleration dominates the water invasion increment, and the water invasion rate grows faster at high displacement. The results of this study provide theoretical support for overflow risk prediction and refined prevention and control in Changqing advanced water injection areas, and also offer references for drilling safety guarantee in similar water injection areas.