The Link Between Lithology and Rock Fractures in the Duvernay 2015 Gussow Conference October 13-15, 2015 Presented by: Amy D. Fox, PhD Geomechanics Director
Duvernay Overview Upper Devonian Resource Play Deposited in a paleoslope and basinal setting In the West Shale Basin ranges from < 1m to > 100m thick Potential for 2-5 BBBLs of liquids and 150 TCF of gas
Duvernay Overview Exploration began quite a while ago, but activity didn t pick up until around 2010 Wide variety of results to date Still considered an emerging play
Duvernay Stratigraphy Developed by Graham Davies Geological Consultants Ltd. as part of the study Based on detailed analysis of 896m of core from 29 wells not regional
Duvernay Sequence Stratigraphy Multi-scale transgressiveregressive cycles define the various units Parasequences from < 1m to 4m+ thickness Up to 33 transgressive lags in a single, 40- metre core Main reservoir facies are laminated, organic-rich mudstones associated with transgressive systems tracts
Duvernay Fracture Types from Core High-angle Natural Fractures Bed-Parallel Parting (BPP) Polished Slip Faces (PSF)
Duvernay Fractures in Image Logs Stress-induced Tensile Fractures Natural Fractures
Fracture-Log Relationship Correlation between Gamma (and TOC) and fractures
Kicks and Inflows - South
Kicks and Inflows - Central
Kicks and Inflows - North
Fractures Love Company? Grossi, 2015, URTeC 2148347 Data from 20 Eagle Ford cores
Brittle-Ductile Couplets Tied to Transgressive-Regressive Cycles Several publications by Slatt and Abousleiman, 2011+ organic-poor, more brittle organic-rich, more ductile
A Brittleness Time-out A rock that is brittle does not deform before it breaks under a load. A rock that is ductile will deform before breaking under a load. There are many types and ranges of ductile behavior with corresponding constitutive models to describe them. Some important factors include mineralogy, temperature, confining stress, loading rate, thermal maturity, and more. The term brittleness has entered the exploration and production lexicon as a means to (imprecisely) describe the ideal rock properties associated with successful hydraulic fracturing. Excerpted from the abstract for Brittleness in shales, an HGS talk by Amie Lucier Hows and Ronny Hofmann, Shell International Exploration and Production, and Yi Yang, Stanford University Brittleness has also become associated with a high likelihood of natural fractures being present. 14
A Brittleness Time-out Mineralogical Brittleness Log/Seismic-based Brittleness high Young s Modulus + low Poisson s ratio = more brittle rock YM Fraccable! PR
Challenging the Assumptions Stress What about the role of S Hmax > S hmin? Is log/seismic-based minimum stress valid? Has it been calibrated? Does it really vary as much as the model says? What effect does the wellbore stress concentration (a.k.a. hoop stress) have on fracture initiation? Rock properties What about the role of rock strength properties (really ANY properties other than Young s Modulus and Poisson s Ratio)? Fracture mechanics Higher Young s modulus can mean smaller fracture width/aperture (could impact proppant placement) and more difficulty in fracture propagation (increase in fracture toughness). Bottom line: It s more complicated.
Measures of Brittleness in the Duvernay kicks/fractures Frac barrier BR Rickman based on YM and PR 17
Measures of Brittleness in the Duvernay BR Rickman BR Dolo/Qtz BR Clay E ps Higher E ps higher fracture toughness, more difficult to fracture 18
Fractures vs. Rock Properties No Fractures due to High Strength YM PR C shale Few Fractures due to High Ductility B carbonate
Fractures vs. Rock Properties Ireton Duvernay Poisson s Ratio Young s Modulus brittleness indices spectral gamma hardness Majeau Lake
Can We Use Logs to Find the Fractures? Density 2400 2800 GR 0 200 300 400 Vp Vs 100 200 5000 5000 Zp Zs 15000 0 10000 20 LR MR 80 100 0 20 PR YM 0.4 80 (example not Duvernay) 2150 2200 2250 2300 2350
A New Way to Find Fractures with Seismic? 1. Relate logs to seismic attributes (example not Duvernay) 2. Classify attributes in a seismic volume traditional interpretation
A New Way to Find Fractures with Seismic? 1. Relate logs to seismic attributes (example not Duvernay) 2. Classify attributes in a seismic volume quantitative interpretation
Summary The link between rock properties and natural and induced fractures has received a lot of attention in unconventional reservoirs. Unfortunately, simple assumptions based on brittleness have become commonplace but are probably not universally applicable. The Duvernay data set shows an interesting, more complex relationship between fractures, lithology and rock mechanical properties, which can t be explained simply using Young s Modulus and Poisson s Ratio. It would be interesting to see if the results from the Duvernay could be extended to quantitative seismic interpretation and used to highlight lithologies that are more likely to be fractured and/or would be easier to hydraulically fracture.
Acknowledgements Thanks to my co-authors Mehrdad Soltanzadeh Neil Watson Graham Davies Thanks to everyone who worked on the Duvernay project Thanks to CSPG and the 2015 Gussow organizers and participants