No abstract

Fines migration is a common cause of permeability and, consequently, injectivity and productivity decline in subterranean reservoirs. Many practitioners implement prevention or remediation strategies to reduce the impact of fines migration on field productivity and injectivity. These efforts rely on careful modelling of the underlying physical processes. Existing works have demonstrated the ability to predict productivity decline by quantifying the extent of particle decline at different fluid velocities. Fluid flows in porous media often involve multiple phases, which has been shown in laboratory experiments to influence the extent of particle detachment. However, no theory has directly accounted for this in a particle detachment model. In this work, a new model for fine particle detachment, expressed through the critical retention function, is presented, explicitly accounting for the immobile fines trapped within the irreducible water phase. The new model utilises the pore size distribution to allow for the prediction of particle detachment at different velocities. Further, an analytical model is presented for fines migration during radial flow into a production well. The model accounts for single-phase production in the presence of irreducible water, which has been shown to affect the extent of fines migration significantly. Combining these two models allows for the revealing of the effects of connate water saturation on well impedance (skin factor growth) under fines migration. It is shown that the higher the connate water saturation, the less the effect of fines migration. The appropriateness of the model for analyzing production well data is verified by the successful matching of 10 field cases. The model presented in this study is an effective tool for predicting the rate of skin growth, its stabilization time and final value, as well as the areal distribution of strained particles, allowing for more intelligent well remediation design. Further, the findings of this study can help for a better understanding of the distribution of fines within porous media and how their detachment might be influenced by pore structure and the presence of a secondary immobile phase.

Fines migration in coalbed methane (CBM) fields comprises a serious environmental and gas-production challenge. The literature widely reports two kinds of fines: potential coal fines, which are a part of the coal body and can be detached by breakage under a significant drag force exerted from the inflowing water, and detrital coal fines, which are attached to the coal body by electrostatic forces. The theory for detrital coal fines migration is well developed. A theory for potential coal fines, where the drag deforms the coal asperities and detaches fines by rock failure, is not available. The objectives of this study are (1) to derive the governing equations for fines generation by breakage using failure criteria, and (2) to predict well productivity during dewatering and gas production using laboratory-based modelling. The micro-model developed is based on beam theory and comprises static rock deformation by the flow-through water and calculating failure criteria by tensile and shear stresses. The failure condition determines the number of fines that detach after the application of each flow rate, allowing determining the maximum retention function of potential coal fines. The breakage micro-model is incorporated into filtration equations that account for fines mobilisation, migration, straining and consequent permeability decline. Eight series of lab flooding data with coal cores have been treated. The close match between the lab and model validates the model developed. The model allows predicting productivity decline due to permeability reduction by fines breakage and straining.