Investigation of Retention and Dehydration of Preformed Particle Gel for Conformance Control in Fractured Carbonates

Summary Preformed particle gel (PPG) treatment has proved to be among the most effective methods to reduce excessive water production in fractured reservoirs. The blocking ability of PPGs to fractures or fracture-like features is highly dependent on injected gel properties and volume. Gel dehydration during extrusion through fracture is common and has a considerable effect on gel properties, transport, and plugging efficiency. As the gel particles propagate through the fracture, continuous dehydration is often associated and causes the gel to concentrate and require high-pressure gradients to move. Dehydration might be desirable to a certain limit because it can help to form a strong gel pack in the fracture; however, overdehydration might cause the gel pack to shrink, reduce the filling volume in the fracture, and deteriorate the gel treatment feasibility. Therefore, it is crucial to carefully control the dehydration process to ensure optimal performance of PPGs in fractured reservoirs. The main objective of this study is to provide a comprehensive assessment of the PPG dehydration effect on gel propagation through fractured carbonates. A fracture model was built to quantify PPG dehydration and retention in fractures under different conditions. Fracture models with and without leakoff matrix were prepared to investigate longitudinal vs. transverse dehydration trends. In a coated fracture model where only the longitudinal dehydration exists, we found that increasing the gel injection flow rate would increase the dehydration and retention, while in a noncoated fracture model where the transverse dehydration is dominant, a filter cake is more likely to form at low flow rate and affect the dehydration rate. A primary judgment of PPGs injection is that the highest practical injection rate should be used for better performance; however, the results in this study suggest that an optimized injection flow rate would avoid further dehydration and gel washout. The outcomes of this study provide new perceptions of PPGs propagation in fractures which would consequently help in better field practice through design optimization.