Many wells completed in soft, poorly consolidated formations tend to underperform relative to the reservoir's production potential. Steep production declines are also indicative of problems with the reservoir. These problems are often attributed to poor drilling and completion practices. Formation-incompatible fluids can be lost to the formation, resulting in significant nearwell permeability loss. Advances in soft-rock stimulation technology have made frac-packing the preferred method for bypassing damaged regions within the formation and for optimizing access to productive zones. Because many soft formations produce fines that can invade the proppant pack and lower productivity, choosing the optimal proppant size for such operations is paramount to overall production-enhancement success.

Numerous studies describe the optimization of proppant size as means of minimizing fines invasion and maximizing pack conductivity. This paper examines other mechanisms that affect pack conductivity and the prevention of fines invasion and migration. The results of this study provide a greater understanding of proppant-pack damage mechanisms and present evidence that proppant coated with chemical agents that make the proppant surfaces "tacky" can significantly improve fracture conductivity.

Microscopic observations of the proppant-pack/formation interface were performed with a dynamic flow model. Images taken from this model indicate that several parameters, such as particle surface charge, wettability, and proppant tackiness, greatly influence fines migration into a proppant pack, regardless of the proppant sizing criteria used. API conductivity measurements performed with realistic pressures, closure stresses, and flow rates were used to confirm micromodel observations.

This procedure provided a quantitative measure of the effects of size criteria and proppant tackiness on fracture conductivity. Fines invasion beyond the proppant-pack/formation interface was determined through postmeasurement microscopic examinations.

The effect of proppant tackifiers on the proppant-pack/ formation interface was also examined, resulting in significant changes in proppant-sizing criteria for frac-packing operations. These findings should have a significant impact on future frac-pack designs.

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