Modeling of Production Decline Caused by Fines Migration in Deepwater Reservoirs

Abstract

Summary Many deepwater wells experience steep productivity declines. Some field observations indicate that this decline is partly attributable to fines-migration effects. In this paper, we present a numerical workflow to simulate the effect (over time) of flow-induced fines migration on production decline in deepwater reservoirs. A permeability-reduction function was extracted from long-term coreflood tests and implemented into a reservoir simulator. Using the permeability-reduction function, production degradation caused by fines migration was simulated in a detailed single-well model. From previous research, it was understood that fines migration does not start until the flow velocity is greater than the critical velocity. After many long-term coreflood tests, or extended fines-migration (EFM) tests, we concluded that the permeability damage induced by fines migration is a function of the pore-volume (PV) throughput (fluid volume flowing through the core divided by the PV of the core). To address these observations, the numerical model was updated such that the interstitial flow velocity was tracked in each individual cell. When the interstitial velocity is greater than the critical velocity, the cell's permeability follows the permeability-reduction trend obtained from laboratory data. Validation of the workflow is performed using a cylinder model to match the laboratory test core-plug data. A detailed 3D model was constructed to study the fines-migration effect in each part of the near-wellbore (e.g., perforation, fracture) region and the reservoir. As expected, fines migration started near the perforation where the flow velocity was the highest. Depending on the permeability-decline rate, the production asymptotes eventually reached a constant value after a certain period. Both the decline rate and the ultimate residual permeability had a strong effect on the final production. Sensitivities were run to study the effect of fines migration in different completions. To the authors’ understanding, this is the first time that laboratory-based fines-migration data were incorporated into a reservoir simulator to predict the production decline using experiment-based fines-migration functions. This workflow will help reservoir engineers predict the damage caused by fines migration, predict production decline, and plan for remediation.