An example from Woodford Shale, Anadarko basin, Oklahoma Characterizing a fault-zone and associated fractures using lab experiments and attribute-based seismic analysis: Zonghu Liao1*(firstname.lastname@example.org ), NabanitaGupta1,2, Ze’ev Reches1, & Kurt Marfurt1 1University of Oklahoma, Norman, Oklahoma 2Current in Shell Oil Company, Houston, Texas
Study area In Canadian and Dewey Counties, 350+ horizontal completions have been made in the Woodford. Woodford shale gas Map Adapted from (Davis, 1988 ) (Gupta, 2012)
Motivations: Controlling fault & Fractures Production Prime principle Drill perpendicular to fracture system! Permeability (Gidley et al, 1990) • Method: • Field observations; • Log image analysis of neighbor-wells • Seismic analysis based on geology.
Time slice cross the Woodford formation Amplitude Positive N Negative A A’ Coherence 1 10, 000 ft 0 Data courtesy of CGG
Hypothesis: it could be a strike-slip fault Time slice
Objectives: • Confirm the structure of strike-slip fault • Characterize the fault and associated fracture system • Suggestions for horizontal well placement Approach: • 1. Clay model experiments as analog for the fault • 2. Geomechanic basis of strike-slip fault • 3. Seismic attribute calculation and analysis • 4. Further analysis and recommendations
First, Riedel shears appear; 5cm The analysis/experiments follows Riedel (1929), Wilcox et al. (1973) Naylor et al (1986), and Reches (1988) etc.
First, Riedel shears appear; ~17-20° Then, Splays appear ~45° Also, P shears occur ~160° 5cm After Naylor et al. 1986; Reches, 1988 et al.
Coherence Amplitude Riedel shears Positive Splay shears P shears Negative Coherence Coherence 1 5000 ft 0 5cm
Dip azimuth Amplitude Positive Influenced by a normal fault Compressed folding Negative Dip azimuth 360 5000 ft 240 120 0
(Sterns, 1976) Curvature Amplitude Positive Fold Depression Negative Curvature Positive 5000 ft 0 Negative
Damage zones C3 C2 C1 Coherence samples normal to the fault 5,000 ft (Dieterichand Smith, 2009; Powers and Jordan, 2010) Background coherence
Conclusions and Discussions • The clay experiments suggest a fault pattern at the proximity of a major strike-slip fault in the basement. • The seismic attributes of dip-azimuth, coherence, and curvature (K1+) could serve as good indicators of strike-slip fault, among which coherence is best to indicate the faults, splay fractures & damage zone; • Compressed fold zones suggested natural fractures for horizontal drilling
Main references • Arroyal, R. M. P. (2009), Characterization and origin of fracture patterns in the Woodford Shale in southeastern Oklahoma for application to exploration and development, Master Thesis, The University of Oklahoma, Norman, OK. • Busetti, S. (2009), Fracturing in layered reservoir rocks, PhD thesis of University of Oklahoma, Norman, OK. • Bradra, H. (2011), Field characterization and analog modeling of natural fractures in the Woodford Sahle, southeast Oklahoma, Thesis of University of Oklahoma, Norman, OK. • Gupta, N., Marfurt, K.J. (2012), Multi-scale characterization of the Woodford Shale in west-central Oklahoma: From scanning electron microscope to 3D seismic, PhD thesis of University of Oklahoma, Norman, OK. • Marfurt, K. J., and J. Rich (2010), Beyond curvature – Volumetric estimation of reflector rotation and convergence: 80th Annual International Meeting of the SEG, Expanded Abstracts, 1467-1472. • Naylor, M.A., Mandl, G., Supesteun, C.H.K. (1986), Fault geometries in basement-induced wrench faulting under different initial stress states, Journal of Structural Geology, (8)7: 737-752. • Reches, Z. (1983), Faulting of rocks in three-dimensional strain field, II, Theoretical analysis, Tectonophysics, 95: 133-156. • Reches, Z. (1988), Evolution of fault patterns in clay experiments. Tectonophysics 145.1, 141-156. • Slatt., R.M., Portas, R., N., Buckner, Abousleiman, Y., O’Borien, N., M., Sierra, R., Philp, P., Miceli-Romero, A., Davis, R., Wawrzyniec, T. (2010) Outcrop/behind outcrop, multi-scale characterization of the Woodford gas shale, Oklahoma: in press. • Staples, E., K. J. Marfurt, and Z. Reches (2011), Curvature-fracture relations in clay experiments, SEG Expanded Abstract, San Antonio, TX, USA, 1908-1912.
Field observation and measurements Core sample Credit: OGS
Log image analysis for the natural fracture system N • log Drilling-induced fracture; Longitudinal-induced fractures; Transverse-induced fractures; Natural fractures S Credit: Oklahoma Shale Gas
T (194580,225000,6660) Unit: ft Azimuth: 358.70 N B(1946000, 224000, 6660) N E
S: surface point; B: bottom point; T: target point; Note: horizontal part BT is not exact in north direction, If you check the coordinates, there is an angle there. N S (1946000,224000,0) 2 mi 3110 ft shale 1 350 ft sand/shale 2 Staples, 2011 3200 ft shale 3 Upper Entry Recommended B (1946000, 224000, 6660) Lower T(1945800, 225000, 6660) Depth, ft Disclaimer: Depth by interpreting the seismic data; Rock properties were assumed based on references