Preformed particle gel transport through fractures

Polymer gel treatment is one of the most cost-effective methods to control water production in mature oil fields. The main objective of gel treatments is to reduce water or gas flow through high-permeability channels or fractures without damaging productive zones. Preformed particle gels (PPGs) have been applied for conformance control because they can overcome some potential drawbacks inherent in an in-situ gelation system. In this study, lab experiments were performed to quantify PPG propagation through fractures and fracture-like channels by using screen models and open fracture models. The main findings in these experiments can guide the selection of best particle gels for specific reservoirs. The results indicate that PPG injectivity increases with fracture width and flow rate; it decreases with brine concentration, on which the PPG swollen ratio is dependent. Increasing particle sizes and injection rates cannot significantly increase injection pressure. The transport mechanisms of swollen PPG through the screen models were identified, and the dominant transport patterns were found to be snap-off and pass and deform and pass . Fracture models showed that PPG propagated like a piston along a fracture during injection and a gel pack formed in the fracture after PPG placement. The degree of gel dehydration in PPG placement is much less significant compared to that in in-situ gel systems. Mathematical models based on the screen tests were developed to characterize the rheological properties of gel placement in fractures and these models were able to predict the pressure gradient and the effective viscosity of swollen PPG extrusion through an open fracture. --Abstract, page iv