Effects of Pore Pressure and Organic Contents on the Brittle-Ductile Transition in Shale Rock Using Geophysical Method

Yasin, Qamar (China University of Petroleum) | Qizhen, Du (China University of Petroleum) | Ismail, Atif (University of Engineering and Technology) | Sohail, GMD (University of Saskatchewan)

OnePetro 

Abstract

The economic success of shale gas plays depends expansively on the brittle-ductile behavior of shale rock. The key parameter that separates the unconventional resources from conventional resources is the formation permeability, so all shale reservoirs need to be hydraulically fractured. Successful hydraulic fracturing requires targeting the most brittle rocks, therefore it is worthwhile to classify the shale in terms of brittle, less brittle, less ductile, and ductile zones. To identify the brittle-ductile transitional zone in shale reservoir, we have correlated the mineralogy-based brittleness index to elastic parameters estimated from well logs. The petrophysical model of the study area were plotted to break a story between brittle mineral contents, organic matter, brittleness indices and pore pressure to differentiate the brittle, ductile and transitional zones. Our results show that change in rock minerals distribution and brittleness index follow the trend in TOC, in less brittle to less ductile zone. In addition, we plotted the data in the crossplot of Young's modulus and Poisson's ratio and λρρ lithology templates, noticed that shale with high quartz and high clay contents fall in less ductile to less brittle zone while shale with high quartz and low clay contents fall in less brittle to brittle zone. The overall observations of our study will support the previous research idea by suggesting the zone of brittle-ductile transition to design the hydraulic fracturing.

Introduction

For a successful shale gas play in a region, the following characteristics (last but not least) need to be considered before going to the exploitation: (a) organic richness (TOC), (b) brittleness, (c) thickness, (d) gas-in-place, (e) permeability, (f) mineralogy, (g) maturation (Ro%) and (h) pore pressure (i) pore geometry (Zhu et al. 2011). Among these characteristics, shale brittleness is more critical to identify the desirable fracturing intervals and propagation for successful shale gas play (Wang and Gale, 2009). Van Dam et al. (2002) also documented in their research that brittleness is an important property that controls the failure process.