The generation of hydraulically produced fractures that are kept open by the use of proppants is a key technology that enables economic production from deep gas reservoirs. Much laboratory attention has been given to the study and prediction of the early productivity of wells completed with this method. Interactions of formation fluids and frac fluids with formation rock and proppant can lead to a host of productivity-reducing mechanisms. Frac fluid damage, scaling, proppant conductivity loss, proppant crushing, and proppant embedment are some of the variables studied in short-term experiments. Little effort, however, has been directed towards the long-term study of these mechanisms on fracture productivity in a laboratory setting.
This paper presents the results of extensive laboratory testing aimed at understanding the interaction of water composition, formation composition, proppant composition, temperature, and closure stress that permit the modeling of certain diagenetic reactions that result in accelerated fracture conductivity loss with time. Some experiments demonstrate that, under certain conditions, the impact of diagenetic reactions on conductivity loss can be significantly reduced by coating mineral surfaces with protective organic films.
This work clearly demonstrates that proppants can react with formation minerals and result in creation of fines, reduction in permeability, and loss of proppant crush strength. This chemistry should be used in selecting proppant that will provide the most sustained productivity. Sustained fracture conductivity can also be achieved under certain conditions by the use of organic filming agents.