T OM W ILSON D EPARTMENT OF G EOLOGY AND G EOGRAPHY W EST V IRGINIA U NIVERSITY M ORGANTOWN, WV Developing a strategy for CO 2 EOR in an unconventional reservoir using 3D seismic attribute workflows and fracture image logs Tom Wilson, Department of Geology and Geography ACTIVITY & ELEMENT FAULT AND FRACTURE ZONE DETECTION AND REDUCED ORDER FRACTURE MODEL DEVELOPMENT FOR RISK ASSESSMENT

Overview Tom Wilson, Department of Geology and Geography 1)Reservoir characterization is developed using analysis of 3D seismic and fracture image logs and seismic attribute workflows for fracture driver development to distribute fracture intensity throughout the reservoir. 2)Analysis of fracture image logs reveals that the dominant open fracture trend within the reservoir is coincident with present-day S Hmax. 3)Outcrop analogs and satellite observations are used to develop model distributions of fracture length, height and spacing 4)Fracture intensity driver is developed using a combination of seismic discontinuities and directional curvature (orthogonal to S Hmax ). 5)Reservoir compartmentalization is interpreted. 6)A strategy for CO 2 EOR is proposed that incorporates placement of injection and production laterals along compartment boundaries and roughly orthogonal to S Hmax.

Location of study area and reservoir structure Tom Wilson, Department of Geology and Geography

Dip line views of structure Tom Wilson, Department of Geology and Geography Basement Madison Tensleep Goose Egg Alcova Morrison Wall Creeks

Tom Wilson, Department of Geology and Geography Fracture characterization using image logs. Open fractures in seal, reservoir and in total S Hmax

Open fracture trends in the reservoir by well and for all wells Tom Wilson, Department of Geology and Geography S Hmax

280’ Fracture Zone Field analogs of seismic discontinuities

Defining fracture parameters- Fracture height distribution Tom Wilson, Department of Geology and Geography

Higher power implies lower probability of higher fractures Tom Wilson, Department of Geology and Geography

Spacing distributions estimated in Freemont Canyon Tom Wilson, Department of Geology and Geography

Variations of fracture intensity in the reservoir Tom Wilson, Department of Geology and Geography

Fracture length distributions from World view ½ meter resolution imagery Tom Wilson, Department of Geology and Geography Outcrop viewed from opposite side of canyon

Local fractures mapped using WorldView imagery Tom Wilson, Department of Geology and Geography

Fracture length distributions (from WorldView imagery) Tom Wilson, Department of Geology and Geography

Seismic discontinuity length distribution Tom Wilson, Department of Geology and Geography

Aperture distributions – log normal with some power law behavior for apertures above ~0.05 mm Tom Wilson, Department of Geology and Geography

Seismic discontinuity detection workflow Tom Wilson, Department of Geology and Geography A variety of post-stack processing workflows have been developed as part of this research. Multiple workflows are usually tested and compared. Some example discontinuity detection workflows are shown at left. Often, discontinuities can be significantly enhanced simply by taking the absolute value of the seismic trace or taking a trace derivative followed by taking it’s absolute value. Low pass filtering is sometimes required to reduce high-frequency noise. Discontinuity detection workflow components

Comparison of amplitude and enhanced seismic data Tom Wilson, Department of Geology and Geography In general, data prep is an iterative process

The derivative enhances high frequency content and introduces a 90 o phase shift Tom Wilson, Department of Geology and Geography

Absolute value doubles apparent spectral content Tom Wilson, Department of Geology and Geography

Extracted discontinuities Tom Wilson, Department of Geology and Geography

NE oriented discontinuities are interpreted to arise from right lateral transpressional shear Tom Wilson, Department of Geology and Geography S1 Fault

Incorporating possible influence of curvature on dominant fracture aperture Tom Wilson, Department of Geology and Geography Maximum directional curvature orthogonal to the dominant open fracture set & S Hmax. S Hmax

Potential compartmentalization within the reservoir suggested by production distribution Tom Wilson, Department of Geology and Geography Log 10 yr cumulative production 5 yr cumulative production (Smith, 2008)

Volume probe through combined discontinuity and directional curvature volume Tom Wilson, Department of Geology and Geography

Composite driver development Tom Wilson, Department of Geology and Geography Discontinuities and directional curvature were extracted from 3D seismic. Conditional statements were used to zero-out high- scoring discontinuities and isolate positive curvature. Only regions with positive curvature were incorporated in the intensity driver. Discontinuity and curvature parameters were upscaled into a model grid and combined to produce an intensity driver that could be used to control the distribution of fractures in the reservoir.

Intensity distribution Tom Wilson, Department of Geology and Geography

Drilling strategy Tom Wilson, Department of Geology and Geography CO 2 injection lateral Production lateral S Hmax Dominant open fracture trend injector producer

Workflow integration Tom Wilson, Department of Geology and Geography Determine Orientation of S hmax from Drilling Induced fractures or Breakouts Analyze Distributions of Dominant Open Fracture Trends Examine directional Curvature at Scale of Seismic Discontinuities Derived 3D Discontinuity Volume Identify potential for compartmentalization Manipulate Attribute Values to Highlight Low and High Permeability regions in Reservoir Upscale and Combine to Provide Fracture Intensity Driver Incorporate Analysis of Field Data to Help Constrain Length, Height and Spacing Distributions Estimate Aperture Distribution Develop DFN Field analogImage log 3D seismic Continued from Discontinuity Detection Workflow

Novel aspects of the approach Tom Wilson, Department of Geology and Geography 1)The new driver addresses the possibility that NE oriented higher-score discontinuities may represent low permeability zones that could compartmentalize the reservoir; and, 2)use of maximum directional curvature orthogonal to the more prevalent N76 o W hinge-oblique open fracture set in the reservoir focuses on that curvature component that could enhance apertures of the dominant fractures set. Curvature in this direction acts in tandem with the orientation of S Hmax inferred from induced fractures observed in the fracture image logs to enhance permeability in the N76W trend.

Recent paper and meeting preparations Tom Wilson, Department of Geology and Geography Developing a strategy for CO 2 EOR in an unconventional reservoir using 3D seismic attribute workflows and fracture image logs: Paper submitted for presentation at the Annual SEG meeting, Sept., 2013, Thomas H. Wilson, National Energy Technology Laboratory and West Virginia University; Valerie Smith, Schlumberger Carbon Services, and Alan Brown, Schlumberger NExT, 5p. Characterization of Tensleep reservoir fracture systems using outcrop analog, fracture image logs and 3D seismic: Abstract submitted for presentation at the Annual AAPG Rocky Mountain Section meeting, Thomas H. Wilson, National Energy Technology Laboratory and West Virginia University; Valerie Smith, Schlumberger Carbon Services, and Alan Brown, Schlumberger NExT

Future work 1. carry through to simulation, or Tom Wilson, Department of Geology and Geography Develop DFN in FRACGEN Field analog Image log analysis Seismic analysis Devise methods for incorporating results from seismic analysis into FRACGEN model Bring in production data Bring in reservoir parameters (Smith, 2008) Incorporate in ROM Simulation and history matching Reservoir Engineering Bring in additional field observations: Alcova and Granite Mountain Anticlines

Future work 2. carry through to simulation in alternative unconventional reservoir Tom Wilson, Department of Geology and Geography The reservoir characterization workflows presented here can be extended to other reservoirs as needed to support NETL priorities. DFN’s, although not presented as part of today’s discussions, have been developed for numerous reservoirs. The methodologies are adaptable and can be readily applied to new settings given sufficient data.