Proppant Backflow Mechanism Of Fractured Gas Wells In The Production Process

Sandfrac is not only a preferred and effective reservoir stimulation technique, but also an important development means for low-permeability oil & gas reservoir. Being significant for the stimulation of the old oil & gas field as well as for the exploitation and exploration of the new, sandfrac has been paid much attention to and developed fast all over the world. However, proppant back-production, which results in serious formation damage and well damage, always occurs during the fractured well production, especially the gas well with high gas flow rate. Being of great complexity, and uncertainty, researches on proppant flowback mainly focus on the precautions and controlling techniques while the mechanism study is few overseas, even much less in China.Based on the the similarity between proppant arch and sand arch and mechanical equilibrium principle, the mechanism of proppant flowing back that occurs during the fractured gas well production is systematically studied and the stability criterion of proppant pack as well as a mechanical and mathematical model are present in this paper. With the method of one-phase flowing including the two-phase, gas flowing law in fracture is further studied and a corresponding flowing model is developed, which is out of the bondage of the traditional β-computing method with empirical formula. Through the crossing point "dP/dx" existing in two above models, an integrated primary model is established. Novel flowing back experiments in this paper validate the correctness of proppant back-production mechanism as well as the reliability of the back-production models. Integrating the primary model with flowing back experiments, an ultimately modified model is obtained.Proppant back-production prediction software is also present in this paper, which can determine the critical gas flow rate and critical daily yield for proppant flowing back. With computed datum, influence and influence degree on proppant back-production of various factors is further qualitatively and quantificationally analysed, including fracture length, fracture width, closure pressure, proppant size, reservoir temperature, water saturation, capillary strength and production pressure difference etc. Quantificationally, the stability of proppant pack is proportional to the closure pressure and proppant size while inversely to the rest; different parameters are of influence degrees. According to the resulted conclusions, the reliability and practicability of the researches in this paper is further confirmed. Preventive recommendations and control contermeasures for proppant back-prodution are also present in this paper, in terms of gas well production and fracturing optimum design.Researches in this paper are of great theoretical and practical significance for ensuring the increasing and stable production as well as the returns-ratio and validity of sandfrac.