Modeling on conductivity of branched fractures of shale gas reservoir considering proppant fragmentation

Key words:  shale gas  branched fracture  fracture conductivity  proppant fragmentation  discrete element numerical simulation

Abstract:

The fractures formed in stimulated reservoir volume fracturing of shale gas can beclassified into three types:the main fracture, the branched fractures and self-supporting fractures. In the initial production stage of horizontal wells, the reservoir pressure decreases rapidly and the fracture closure pressure can be significantly increased. The long-term conductivity of the branched fractures can directly affect the total production of the wells. In this study, a rock mechanics testing equipment coupled with multi-parameters was used to measure the conductivity of branched fractures using a new experimental method. Then based on the characteristics of shale reservoirs, a seepage-stress coupling model for the conductivity of branched fractures was established, and the effects of many parameters on the fracture conductivity were analyzed, including proppant crushing, proppant placement, the elastic modulus of reservoir formation, the surface morphology of the fractures and combination of different proppants. The results show that, under a certain proppant concentration in the branched fractures, the total fracture conductivity with part of single layers being proppant placed is better than that all the single layers are placed. In the case of a lower closure pressure using different proppant size combinations, the larger the particle size, the higher the fracture conductivity.