The Link Between Lithology and Rock Fractures in the Duvernay 2015 Gussow Conference

Transcription

1 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

2 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

3 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

4 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

5 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

6 Duvernay Fracture Types from Core High-angle Natural Fractures Bed-Parallel Parting (BPP) Polished Slip Faces (PSF)

7 Duvernay Fractures in Image Logs Stress-induced Tensile Fractures Natural Fractures

8 Fracture-Log Relationship Correlation between Gamma (and TOC) and fractures

9 Kicks and Inflows - South

10 Kicks and Inflows - Central

11 Kicks and Inflows - North

12 Fractures Love Company? Grossi, 2015, URTeC Data from 20 Eagle Ford cores

13 Brittle-Ductile Couplets Tied to Transgressive-Regressive Cycles Several publications by Slatt and Abousleiman, organic-poor, more brittle organic-rich, more ductile

14 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

15 A Brittleness Time-out Mineralogical Brittleness Log/Seismic-based Brittleness high Young s Modulus + low Poisson s ratio = more brittle rock YM Fraccable! PR

16 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.

17 Measures of Brittleness in the Duvernay kicks/fractures Frac barrier BR Rickman based on YM and PR 17

18 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

19 Fractures vs. Rock Properties No Fractures due to High Strength YM PR C shale Few Fractures due to High Ductility B carbonate

20 Fractures vs. Rock Properties Ireton Duvernay Poisson s Ratio Young s Modulus brittleness indices spectral gamma hardness Majeau Lake

21 Can We Use Logs to Find the Fractures? Density GR Vp Vs Zp Zs LR MR PR YM (example not Duvernay)

22 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

23 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

24 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.

25 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