In less than two weeks, at URTec 2015 in San Antonio, I will be presenting two papers on geomechanics of the Duvernay Formation based on the Canadian Discovery’s study on this play. The papers provide comprehensive information on different geomechanical components, workflows and results of the study.
The first paper (to be presented on Monday, July 20) discusses some of our interesting observations based on detailed reviews of drilling experience for several wells that confirm the existence of different regional drilling patterns in the play. The paper demonstrates how using in-situ stresses, wellbore stability analysis, and core descriptions can help with explaining the reasons behind these differences, a major one being the potential influence of existing carbonate reefs on the geomechanical response of the play.
The second paper (to be presented on Tuesday, July 21) reviews the integrated workflows developed and implemented to combine core description and geomechanical, geochemical, and petrophysical data to identify and characterize different fracture fabrics. The paper also shows how integrating these data can provide a reliable methodology for characterizing rock fraccability and brittleness. Such a methodology may be a strong base for using log and seismic data for fracture characterization through quantitative interpretation.
In case you are also attending the conference, it would be great to have you there for the presentations and hear your questions, comments, and suggestions. I may also be found at the CDL booth in the exhibit area for most of the conference time. The abstracts for the papers are given below.
A Regional Review of Geomechanical Drilling Experience and Problems in the Duvernay Formation in Alberta
Mehrdad Soltanzadeh, Amy Fox, Sarah Hawkes, David Hume
The Duvernay Formation has been an attractive unconventional play for several producers during the last few years, and the number of drilled wells in this play has been increasing rapidly. Nevertheless, drilling in this formation is usually considered a challenging practice due to the extremely high stresses and pore pressures that can be encountered. Drilling in the Duvernay and its overlying formation, the Ireton, has shown a wide variety of drilling incidents such as sloughing, tight spots, bridges and lost circulation. This paper summarizes the results of a comprehensive regional review of drilling experience for 43 Duvernay wells. In this review, the details of drilling experience for these wells were documented using a graphical approach that captures important information on the details of drilling incidents including depths and dates, along with information on mud weights and well trajectory. As an initial part of a broader regional geomechanical study of the Duvernay, these data were statistically analyzed to identify the stratigraphic and spatial variation of drilling patterns throughout the study area. The results revealed significant differences between drilling patterns in the three major active areas of the play including south (Willesden Green and Edson), central (Kaybob), and the northwest regions. In general, wells in the central region can be drilled with lower mud weights than other regions, and experience fewer drilling problems. Because pore pressure in the Duvernay Formation in this area is as high as in the other two regions, the difference in drilling experience was attributed to considerable differences in in situ stress, which appears to be related to the presence of Leduc reefs. These stress differences were confirmed by modelling and distribution of fractures in the study area.
Application of Mechanical and Mineralogical Rock Properties to Identify Fracture Fabrics in the Devonian Duvernay Formation in Alberta
Mehrdad Soltanzadeh, Graham Davies, Amy Fox, David Hume, Nasir Rahim
Mechanical rock properties, along with in situ stresses and pore pressure, play critical roles in forming fractures in reservoir rocks. As part of a regional geomechanical analysis of the Duvernay resource play, several Duvernay cores were analyzed in detail, including the identification of different types of natural and induced fractures. The observed natural fractures include uncategorized natural fractures and polished slip faces (PSF) with rare presence of cleavage. Coring-induced fractures included petal and petal-centreline fractures and bed parallel parting (BPP). Comparison of the presence of the different fracture fabrics with mechanical and mineralogical properties of the rock revealed strong correlations between rock properties and fracture types. Such correlations may be efficiently implemented for characterization of fracture fabrics in the rock using wireline logs or seismic surveys. The observed natural and induced fractures in the cores have also been utilized to revisit and verify the concept of rock brittleness. The analyses show that, as a result of high clay content and overpressuring, the conventional mineralogical and mechanical brittleness indices do not adequately describe the variability of the Duvernay Formation stratigraphic units. Alternative indices developed for this study (i.e., plane-strain Young’s modulus and clay-based brittleness index) seem to be able to represent the mechanical behaviour of rock much more precisely. This study suggests that using natural and induced fracture fabrics observed on image logs and in cores, along with mineralogical and mechanical rock properties, is a more practical approach to assist with identifying sweet spots in unconventional plays.