Produced water is the largest by-product by volume in the petroleum industry. About 90% of it is re-injected into subsurface, and this is the single largest operating cost in the industry. A major concern in water injection projects is the decline of injectivity, which is controlled by formation damage from particle filtration near the wellbore. To predict injector performance, a comprehensive approach is required which encompass the understanding on particle filtration, thermo- and poro-elasticity, and fracture mechanics.
Solid particle filtration in a proppant pack is the primary factor that controls the injectivity decline in hydraulically fractured injection wells. The injection well performance may decline significantly depending on filtration degree in this high velocity range. There is no experimental data for the filtration coefficient in this high velocity ranges.
We measured filtration coefficients in high velocity flows encountered in an actual proppant pack. Solid concentrations and pressure drops across proppant pack sections were measured under various flow rates and proppant sizes. Our experiments show that high velocity filtration behavior is different from prior correlations based on low velocity filtration. The deviation from correlations can be understood based on theories of the hydrodynamic detachment of particles. The proper estimation of the filtration coefficient enabled us to analyze the impact of injection rates and proppant selection to better predict long-term injector performance.
Our experiments accurately capture, for the first time, how particle filtration at high fluid velocity affects injector performance over the injector life. The model with proper filtration physics was useful for proppant selection and specification of injection water quality. It allowed us to estimate fracture dimensions and the long-term injectivity in hydraulically fractured injection wells. Based on our models, injector types and water treatment facilities can be properly selected. Our unique data set can be applied to other disciplines as well.