Factors Affecting the Stability of Proppant in Propped Fractures: Results of a Laboratory Study

Abstract

Abstract Factors controlling the stability of proppant in propped fractures were identified and investigated experimentally. The results indicate that the absolute size, distribution and type of proppant may affect stability, and hence the likelihood of proppant flowback. The extent of embedment of the proppant into the rock determined by closure stress and rock hardness) was found to play a key role in stabilising the pack. in addition, channels, which may form due to proppant settling before fracture closure, were found to significantly reduce stability. These are, therefore, favourable sites for proppant flowback. A numerical study has been used to determine lengths of unpropped fractures which may be maintained open due to the rock stiffness. The implications of these results for well productivity and the understood mechanisms of proppant flowback, in the field, are discussed. Introduction The flowback of proppant from hydraulically fractured wells is of significant concern to the industry. In addition to problems of valve, line and choke erosion, there is the potential for a loss in near wellbore fracture conductivity. Furthermore, expensive separation facilities are required to filter out proppant from the hydrocarbons, and these may necessitate manning the rig. While substantial work has been carried out to identify means of reducing the amount of proppant flowed back, far less effort appears to have been directed towards understanding the mechanisms which determine whether or not a given well will back produce proppant. Hence it is difficult to decide a priori what preventative measures should be taken. The uncertainty has been concisely put by Daneshy (1) who said of techniques to reduce flowback "None of these methods works all the time, and no criteria are available to know when to do what". Various methods have been devised to reduce proppant flowback. These include resin-coating the proppant, installing mechanical screens and modifying the completion design. Resin-coated proppants have been used successfully in certain environments. P. 569^