Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Laboratory study of proppant on shale fracture permeability and compressibility Yuling Tan a,b,c , Zhejun Pan c, ⁎ , Jishan Liu d , Xia-Ting Feng a,e , Luke D. Connell c a State Key Laboratory of Geomechanics and Geotechnical Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, Hubei 430071, China b University of Chinese Academy of Sciences, Beijing 100049, China c CSIRO Energy, Private Bag 10, Clayton South, VIC 3169, Australia d School of Mechanical and Chemical Engineering, The University of Western Australia, 35 Stirling Highway, WA 6009, Australia e Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines, Northeastern University, Shenyang 110004, China ARTICLE INFO Keywords: Shale gas Microscopic X-ray computed tomography Proppant Permeability anisotropy Compressibility ABSTRACT Hydraulic fracturing is key for shale gas production and fracture permeability or conductivity is one of the most important parameters for gas production rate. Investigating the proppant distribution and fracture permeability in the field is difficult, therefore, laboratory study is a good alternative. In this work, the effect of the layer number and type of proppant on fracture permeability and compressibility were investigated. A cubic shale sample from the Cambrian Niutitang Formation at Sangzhi, Hunan Province, China, was used in this work. Sands and glass beads of different number of layers were added into an artificial fracture and seven cases, including original sample, non-propped fracture, and four kinds of propped fractures were considered. Permeability at three gas pressure steps and five confining pressure steps were measured in each case at two flow directions. Microscopic X-ray computed tomography was used to detect the distributions of proppant, and the relationship with permeability and its anisotropy was studied. A permeability model combining the stress and Klinkenberg effects was used to match experimental data and a new fracture compressibility model was proposed to predict the change of fracture compressibility with the layer number of proppant. It was found that permeability and compressibility of proppant supported fracture are closely related to proppant packing pattern and layer number, as well as the permeability anisotropy. These results improve our understanding on permeability behaviour for the proppant supported fracture and can assist in the model of fracture permeability and simulation of shale gas production. 1. Introduction Shale gas has become an important natural gas resource in recent years. Production of shale gas increased drastically in the past decade in the U.S. and reached 15.2 Tcf (0.43 Trillion m 3 ) in 2015, about 50% of total U.S. dry natural gas production [1,2] and triggered significant interest worldwide [3,4]. As shales have very low porosity and per- meability, the success of shale gas development owe significantly to the multi-staged hydraulic fracturing technology in horizontal wells [5]. Fracture will dynamically extend in length and aperture to form com- plex fracture network under the process of multi-staged hydraulic fracturing [6,7]. Moreover, the economic development of shale gas requires not only the large-sale complex fracture system in the re- servoir, but also the increased and sustained fracture conductivity [8]. The fracture conductivity, defined as the product of permeability and fracture aperture, is a key indicator to evaluate the effectiveness of fracturing [9]. During hydraulic fracturing, proppant particles are mixed with fracturing fluids and then injected into fracture system to prevent fracture closure, hold fractures open, and obtain high fracture conductivity [10]. Shale fracture conductivity plays a critical role in determining the long term production of shale wells, so studies on the impact of proppant on the fracture conductivity are highly desirable. Laboratory measurements on propped-fracture conductivity are important for analysing reliable well performance and optimizing fracturing design [11]. The fracture conductivity is affected by rock strength [12], stress [13], the proppant material, size, added amount, distribution and embedment, etc. [10,14–16]. Experimental studies on conductivity for proppant supported fracture of rock cores have been performed [16–18], demonstrating that the permeability of propped sample was drastically improved from the original sample. The effect of proppant embedment on the fracture conductivity on rock cores propped with two types of proppants at different concentrations was https://doi.org/10.1016/j.fuel.2018.02.141 Received 22 August 2017; Received in revised form 19 February 2018; Accepted 21 February 2018 ⁎ Corresponding author. E-mail address: Zhejun.Pan@csiro.au (Z. Pan). Fuel 222 (2018) 83–97 0016-2361/ © 2018 Elsevier Ltd. All rights reserved. T