Fracture Conductivity of Shale Considering Sample Soaked in Slick Water

Abstract

ABSTRACT: Hydraulic fracturing technology is an effective method to develop shale gas, and fracture conductivity contributes for the shale gas well production. In order to study the factors affecting the conductivity of shale gas well, the conductivity was tested with FCES-100 system. After soaking in slick water for 48 hours, the conductivity can be reduced by about 28.79%. Fracture geometry has a great influence on the conductivity, both diverting fractures and branching fractures make fluid flow channels longer, thus reducing the conductivity by 33.34% at the most. The effect of the stress loading rate on the conductivity couldn’t be ignored as well, and the higher the stress loading rate, the lower the conductivity. The conductivity of 100 mesh ceramsite decreases by 82.67% when the closure pressure increases from 5 MPa to 50 MPa. For long-term conductivity tests, the conductivity decreased quickly in the early stage when the closure pressure reached 50 MPa at approximately 64 h. Relevant conclusions could provide guidance for hydraulic fracturing treatment according to the experimental results. 1. INTRODUCTION Hydraulic fracturing technology is an effective method to develop shale gas, and fracture conductivity contributes for the shale gas well production. The experimental test of fracture conductivity have been studied by many researchers. Terracina J.M et al. (2010). developed the long-term baseline conductivity laboratory test for proppants, the tests attempt to establish how the factors such as proppant fines, embedment, proppant flowback could be used to explain and support the results of the field cases. Rivers M. et al. (2012) studied the proppant fracture conductivity with high proppant loading and high closure stress. Increasing proppant concentration in the fracture showed higher conductivity values in same cases, while increasing the effective closure stress during and individual test resulted in a significant loss in conductivity for all cases. Zou Y.S et al. (2013). cleaved the shale rock along the cracks and the rough surface of cracks was used to form shale samples, and the conductivity of fractures was tested in hydraulic fracturing network of shale gas reservoir.Zhu Y.H. et al. (2014) obtained the influence rule of proppant type, particle size, closure pressure and proppant concentration on fracture conductivity through analysis, and obtained the multiple regression function formula for calculating shale conductivity through fitting with a large number of test data. Bi W.T. et al. (2016) carried out an experiment for the first time to simulate the influence of formation stress fluctuation caused by opening and closing process on the conductivity of shale reservoir. Zhao Y.D. et al. (2017) used FCS-842 fracture conductivity system to test the long-term conductivity under simulated formation conditions, and made microscopic observations of various types of rock samples and proppants after the experiment. Mittal A. et al. (2018) and Gupta et al. (2019) investigate the impact of fines migration, proppant concentration, size and presence of different volcanic ashes on fracture conductivity along with different conductivity impairment mechanisms including proppant crushing, embedment and diagenesis under simulated reservoir conditions.