Study on Flowback Characteristics and Composition of Flowback Fluid in Ultra-low Permeability

Dynamic analysis of flowback fluid composition is considered to be an effective means to evaluate reservoir characteristics and guide fracturing operation. Taking the natural gas well fracturing operation in the tight sandstone reservoir in the eastern Ordos Basin of Changqing Oilfield as the research object, this work analyzes by X-ray fluorescence spectrometry the ionic composition and volume change of the flowback fluid against different flowback times after the pressure detection in gas wells at various reservoir layers. At the same time, after the fracturing fluid penetrates into the rock and through the tests of pH values, chemical oxygen demand (COD), rheology, surface tension and contact angle, etc., the process of mineral dissolution and migration in reservoir and the interaction mechanism between fracturing fluid and reservoir rock and the ion source of post fracturing flowback fluid was revealed. It is found that the ion contents in the flowback fluid after fracturing tend to be stable after 10∼20 days and most of the ion contents tend to be stable after about 18 days. It is around 19 days for the volume of the flowback fluid to be stable and around 20 days when the daily gas production becomes steady. The time duration for the three parameters is basically similar. Therefore, the variation characteristics of the ion contents of the flowback fluid after fracturing can reflect the interaction between the fracturing fluid, shale and proppant. This work is expected to provide a theoretical basis for further understanding of the interaction mechanism between tight sandstone and fracturing fluid, and provide a theoretical basis for optimizing production system. © 2023 Science Press. All rights reserved.