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Shear-Wave Splitting and Attenuation Analysis of Downhole Microseismic Data for Reservoir Characterization of the Montney Formation, Pouce Coupe, Alberta

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Shear-Wave Splitting and Attenuation Analysis of Downhole Microseismic Data for Reservoir Characterization of the Montney Formation, Pouce Coupe, Alberta SHEAR-WAVE SPLITTING AND ATTENUATION ANALYSIS OF DOWNHOLE MICROSEISMIC DATA FOR RESERVOIR CHARACTERIZATION OF THE MONTNEY FORMATION, POUCE COUPE, ALBERTA by Ben P. Andrews © Copyright by Ben P. Andrews, 2016 All Rights Reserved A thesis submitted to the Faculty and the Board of Trustees of the Colorado School of Mines in partial fulfillment of the requirements for the degree of Master of Science (Geo- physics). Golden, Colorado Date Signed: Ben P. Andrews Signed: Dr. Thomas L. Davis Thesis Advisor Golden, Colorado Date Signed: Dr. Terence K. Young Professor and Head Department of Geophysics ii ABSTRACT Two microseismic waveform analysis methods were performed for reservoir characteri- zation of the Montney Formation at Pouce Coupe, Alberta. Microseismic events recorded on two downhole arrays during the hydraulic fracture stimulation of three production wells formed the dataset for both methods. The first method involved the calculation of shear-wave attenuation factors through a comparison of observed and expected P/Sh amplitude ratios. The method was anticipated to help infer the presence of fluid-filled fractures however a number of limitations were identified. The assumption of a single source mechanism introduced significant uncertainty to the expected amplitude ratios. This uncertainty becomes increasingly amplified as source- vectors approach the modeled nodal planes, resulting in a strong azimuthal bias to the shear- wave attenuation factors. The accuracy of this method was also degraded by not accounting for variable baseline attenuation of the P- and Sh-waves. Future success with this method will likely require simultaneous surface and downhole microseismic monitoring such that source-mechanisms can be accurately determined for each event. The second method performed was a microseismic shear-wave splitting analysis. A total of 48,987 3C seismograms yielded 1,136 reliable splitting measurements. Measurements indicate at least orthorhombic symmetry within the Pouce Coupe reservoir consisting of horizontally layered fabric and two near-vertical natural fracture sets roughly parallel and perpendicular to SHMax. This interpretation corroborates previous image log analysis from nearby Farrell Creek Field as well as focal mechanism and surface shear-wave splitting studies at Pouce Coupe. A strong temporal correlation was observed between shear-wave splitting measurements and completion data. A continued increase in the magnitude of splitting during hydraulic stimulation coupled with a rotation of the fast polarization indicate that reservoir anisotropy iii becomes dominated by near-vertical hydraulic fractures roughly parallel to SHmax. Temporal observations made perpendicular to SHmax display a similar but less significant response at the onset of the completion process. This may suggest activation of the natural fracture set perpendicular to SHmax, but limited propagation of any hydraulic fractures in that direction. This study highlights the value as well as some of the practical challenges associated with microseismic waveform analysis for reservoir characterization purposes. Future improvement of semi-automated analysis techniques that are adaptive to the waveform characteristics of individual source-receiver records will help make the most of large microseismic datasets for such purposes. iv TABLE OF CONTENTS ABSTRACT ......................................... iii LISTOFFIGURES .................................... viii LISTOFTABLES ......................................xii LISTOFSYMBOLS.................................... xiii LISTOFABBREVIATIONS ................................ xv ACKNOWLEDGMENTS ..................................xvi DEDICATION ....................................... xvii CHAPTER1 INTRODUCTION ...............................1 1.1 Motivation...................................... 2 1.2 AimsandObjectives ................................ 3 1.3 Geology ........................................4 1.4 HydrocarbonProductionfromtheMontney . ......6 1.5 PouceCoupe ....................................11 CHAPTER 2 DATA AVAILABILITY AND PREVIOUS STUDIES . 15 2.1 SeismicData ....................................15 2.2 MicroseismicData ................................ 16 2.3 CompletionsandProductionData. ..... 22 2.4 PreviousStudiesatPouceCoupe . .... 25 CHAPTER 3 SHEAR-WAVE ATTENUATION FROM MICROSEISMIC EVENTS . 30 3.1 Methodology ....................................30 v 3.2 AssumptionsandUncertainties . 32 3.3 ResultsandInterpretation . ..... 35 3.3.1 Example 1 - Inferring Areas of Natural Increased Attenuation . 35 3.3.2 Example 2 - Inferring the Presence of Hydraulic Fluid-Filled Fractures . 37 3.3.3 Example 3 - Implications for Understanding Production .........39 3.4 ConclusionsandRecommendations . ..... 43 CHAPTER 4 SHEAR-WAVE SPLITTING THEORY . 45 4.1 SeismicAnisotropy ................................ 45 4.2 Shear-WaveSplittingTheory. ..... 46 4.2.1 TransverselyIsotropicMedia. .... 47 4.2.2 OrthorhombicMedia ............................ 49 4.3 Interpretation Theory for Microseismic Shear-Wave Splitting . 51 4.4 Advantages of Anisotropy Estimation from Microseismic . ..........53 CHAPTER 5 SHEAR-WAVE SPLITTING FROM MICROSEISMIC . 56 5.1 Methodology ....................................56 5.1.1 DataSelection................................ 56 5.1.2 WaveformFiltering ............................. 60 5.1.3 Multi-WindowParameterConfiguration . 65 5.1.4 Semi-AutomatedSplittingAnalysis . 67 5.1.5 Results.................................... 72 CHAPTER 6 INTEGRATED INTERPRETATION OF MICROSEISMIC SHEAR-WAVE SPLITTING AT POUCE COUPE . 78 6.1 SingleHomogeneousAnisotropySystem . .... 78 vi 6.2 Temporal Variations in Shear-Wave Splitting . ..........83 6.2.1 Cluster 1 - Temporal Splitting Variations Parallel to SHmax ....... 86 6.2.2 Cluster 2 - Temporal Splitting Variations Perpendicular to SHmax . 88 6.3 LimitationsandUncertainties . ..... 93 CHAPTER 7 CONCLUSIONS, RECOMMENDATIONS AND FUTURE WORK . 96 7.1 Recommendations................................. 98 7.2 FutureWork.....................................99 REFERENCESCITED .................................. 101 APPENDIX - FREQUENCY FILTERING . 106 vii LIST OF FIGURES Figure1.1 LocationmapofPouceCoupe . .....5 Figure 1.2 Paleogeographic map of the Western Canadian SedimentaryBasin . .6 Figure 1.3 Regional map of the Montney and its major rock types ...........7 Figure 1.4 A schematic of the depositional environment of the Montney . .8 Figure 1.5 Map displaying the distribution of Montney productionwells . .9 Figure 1.6 Hydrocarbon production from Montney gas wells . ...........9 Figure 1.7 Average gas production rates in the Montney . .........10 Figure 1.8 Schematic stratigraphic section of the Montney reservoir. 11 Figure 1.9 A regional stress map of Alberta and Eastern British Columbia . 12 Figure 1.10 A 3D view of the well geometry at Pouce Coupe . ........13 Figure 1.11 Vertical section of the well geometry at Pouce Coupe ...........14 Figure 2.1 Timeline of data acquisition at Pouce Coupe . ..........16 Figure 2.2 Seismic acquisition geometry at Pouce Coupe . ..........17 Figure 2.3 Downhole 12-tool array deployed in the 9-7 vertical observation well . 19 Figure 2.4 Velocity model used for microseismic processing atPouceCoupe . 20 Figure 2.5 Event maps of the five single array microseismic subsets.......... 21 Figure 2.6 Completions chart for the 7-7 treatment well . ...........24 Figure 2.7 Production rates for the three study wells at Pouce Coupe ........ 25 Figure 2.8 Time-lapse shear-wave splitting analysis from 3D surfaceseismic . 26 Figure 2.9 Composite focal mechanism solutions at Pouce Coupe...........27 viii Figure 2.10 Isochron map of the two best rock quality clusters and microseismic eventsfromtheMontneyCandD . 28 Figure 2.11 Microseismic events, production data, and time-lapse time-shifts of the overburdenatPouceCoupe. 29 Figure 3.1 Source mechanism coordinate geometry for a strike-slipfailure . 32 Figure 3.2 The influence of a single source mechanism assumption and nodal planes on the calculation of shear-wave attenuation factors ........34 Figure 3.3 Map of shear-wave attenuation factors for the 2-7 treatmentwell . 36 Figure 3.4 Shear-wave attenuation factors vs event time for the 8-7 treatment well . 37 Figure 3.5 Map of shear-wave attenuation factors for the 8-7 treatmentwell . 38 Figure 3.6 Shear-wave attenuation factors vs event time for the 7-7 treatment well . 39 Figure 3.7 Map of shear-wave attenuation factors for the 7-7 treatmentwell . 40 Figure 3.8 Surface shear-wave splitting map from the baseline 3D seismic survey . 41 Figure 3.9 Vertical section of microseismic events from the 7-7 treatment well scaled by their shear-wave attenuation factors . ..... 42 Figure 3.10 Spinner log production data compared to time-lapse time-shifts in the overburden................................... 43 Figure 4.1 A schematic of shear-wave splitting in Transversely Isotropic Media . 48 Figure 4.2 An Orthorhombic model consisting of two vertical and orthogonal fracture sets embedded within a horizontally layered background . 49 Figure 4.3 Phase velocity sheets for an Orthorhombic medium . ...........51 Figure 4.4 Upper hemisphere projections of the shear-wave splitting signature for VTI,HTI,andOrthorhombicmedia . 53 Figure 4.5 Polar plot of source-vectors for all recorded source-receiver pairs . 55 Figure 5.1 Waveform moveout for an event recorded on the horizontal 8-7 array . 57 Figure 5.2 Waveform moveout for an event recorded on the vertical9-7array . 58 ix Figure
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