Fracture-conductivity loss caused by geochemical interactions between man-made proppants and formations

The selection of proppant to provide highly conductive pathways in hydraulically-generated fractures is typically based on the proppant crush strength, permeability, availability, and cost. Extensive laboratory data determined conductivity values, obtained using API standardized methods at a variety of simulated well conditions, are available for most proppants. However, post-fracture stimulation well testing indicates that these values are often one to two orders of magnitude too high. In many fields, the productivity of fractures declines rapidly, requiring frequent re-stimulation treatments to remain economically viable. Proppant crushing and embedment, fracturing-fluid damage, and fines invasion are proppant-pack permeability damage mechanisms that have been used to explain this loss of productivity. This paper reports on recent studies that have determined that alumina-based proppant materials may promote geochemical reactions that can occur at a surprisingly rapid rate, even at moderate temperatures, resulting in the loss of porosity and permeability and the creation of fines in the proppant pack. The compatibilities of several man-made proppants ranging from lightweight ceramics to high-strength bauxites with a variety of formations are presented.