Abstract Micro-sized proppants are increasingly applied in hydraulic fracturing to prop micro-fractures and expand the stimulated reservoir volume (SRV) in unconventional formations. Although some oilfields have observed production gains from their use, others have encountered well performance deterioration. Given that the design of micro-sized proppant injection remains largely empirical, the mechanisms underlying reservoir damage caused by these proppants are not fully understood. This uncertainty has discouraged their broader adoption in some fields. To address this, a model was developed using the linear elastic deformation theory for both formation rock and proppant particles, quantifying conductivity changes in micro-fractures containing a partial monolayer of these proppants. By comparing the predicted propped fracture conductivity with its initial value, this study highlights when proppant placement enhances or reduces conductivity, categorizes damage mechanisms, and introduces a conceptual framework distinguishing "improvement zones" from "damage zones." A propped fracture productivity model was developed by integrating the conductivity model, resulting in a diagram that correlates folds of productivity increase with stimulation distance. Modeling results indicate that the fold increase in well productivity does not monotonically rise with the increasing placement distance; instead, there is a turning point beyond which further placement reduces productivity gains. A case study of micro-sized proppant stimulation from a Coalbed Methane (CBM) reservoir in the Qinshui Basin, China demonstrates that as the dimensionless stimulation radius increases from 0 to 0.86, the folds of productivity increase rise from 1.0 to 5.9. However, when the radius exceeds 0.86, productivity gains begin to decline. This suggests that the optimal stimulation radius is approximately 86% of the drainage radius; stimulating an entire drainage zone does not yield the highest productivity. The underlying mechanism is that micro-fractures farther from a wellbore experience lower closure pressures during production, so the proppants' contribution to fracture opening is outweighed by their detrimental impact on micro-fracture permeability. However, notably, the fold increase in productivity rises from 1.6 to 4.7 as the injection rate of proppant-carrying fluid increases from 1.0 m3/min to 10.0 m3/min. A higher fluid injection rate always leads to better stimulation effectiveness. This work clarifies the mechanisms behind productivity impairment, emphasizing both the risks and opportunities of micro-sized proppant use. By identifying optimal design parameters, it provides practical guidance to improve stimulation strategies and maximize unconventional reservoir development.
Liu et al. (Mon,) studied this question.