Deformation of shales at reservoir conditions. To measure the mechanical properties of shale rocks recovered from different shale formations, two types of deformations experiments were performed at varying confining pressures, pc, and temperatures, T. First, intact samples were deformed at constant strain rate, , allowing to determine the triaxial compressive strength, TCS, and static Young’s modulus, E, from measured stress-strain curves. Secondly, sample deformation was performed at constant stress, , to unravel the sample’s creep properties from observed creep curves. To investigate the indentation behavior of proppants into the shale matrix, additional creep tests were performed on split samples containing a monolayer of proppants. We used proppants composed of > 99 wt% quartz. Samples examined include Carboniferous Upper and Lower Xxxxxxx (BOS) shale (UK) recovered from boreholes (Preese Hall1, Xxxx Xxxx Moor) and an outcrop located in Lancaster, which is believed to be England’s most prospective shale play. In addition, we studied Cambrian Alum (ALM) shale (DK), Lower Jurassic Posidonia (HAR, HAD, DOT) shale (GER), Haynesville (HVS) shale (US) and Marcellus (MAS) shale (US). The experiments were focussed on the comparison between mature, clay – rich Posidonia (HAR) shale and mature, quartz – rich Upper Xxxxxxx shale, recovered from an outcrop (BOS_OC). The latter was selected due to insufficient availability of borehole core material required to perform deformation tests. Detailed petrophysical data including porosity measured by He - pycnometry of all investigated samples are given in Table 1. All experiments were performed on cylindrical samples (length = 20 mm, diameter = 10 mm), prepared perpendicular to bedding, using a Paterson type deformation apparatus (Paterson 1970). The samples were jacketed by copper sleeves to prevent intrusion of the gas-confining pressure medium. Recorded axial force were converted to axial stress assuming constant volume deformation and corrected for the strength of jackets. Axial strain was determined from measured axial displacement and corrected for system compliance. In what follows we briefly describe the procedures implemented for (i) constant strain rate tests, (ii) constant stress tests, and (iii) constant proppant indentation tests. Table 1: Mineralogical composition, density and organic content of investigated samples. Sample VRr [%] [ ] [vol%] TOC [vol%] Cly [vol%] Mca [vol%] Cb [vol%] Qtz [vol%] Py [vol%] Fsp [vol%] CTMP [vol%] Cb [vol%] QFP [vol%] HAR...
