One or two deficiencies of current fault seal analysis methods

Transcription

1 Shell Exploration & Production One or two deficiencies of current fault seal analysis methods Scott J. Wilkins and Stephen J. Naruk Copyright 2003 SIEP B.V. Structure, Traps and Seals Team Bellaire Technology Center Houston, TX

2 Geologic Time Scales (column heights) No consideration of hydraulic behavior during fault slip. Wilkins, S.J. and Naruk, S.J., 2007, Quantitative analysis of slip-induced dilation with application to fault seal, AAPG Bulletin, v91, Production Time Scales (permeability) Accurate prediction of fault seal behavior for small faults in clean sands (deformation bands).

3 Static Seal Capacity Many faults seal << than the maximum possible column heights Seal capacity (capillary entry pressure, column height, etc.) Weak point Fault rock descriptor (CSP, SGR, etc.) Copyright SIEP B.V. SIEP B.V. Points showing only the maximum seal capacity / fault rock descriptor value for each fault

4 Potentially Important Parameters That Influence Static Seal Capacity structural model >> fault zone architecture & resulting gouge distribution>> capillary entry pressure subseismic architecture timing of charge vs. faulting gouge/smear minerology & petrophysical properties Copyright SIEP B.V. SIEP B.V. fault dynamics (i.e., behavior during slip)

5 Active, Sealing Normal Faults Is the sealing behavior of active faults different from dormant faults? - critical stress? But charge & slip is contemporaneous Fault extends to within a loop of seafloor, forms central collapse graben, and retains ~175 m oil column - no stratigraphic influence - discount for active faults?

6 Seafloor Expression of an Active, Leaking Fault Fault Scarps Vent Pock Marks seafloor dip map showing fluid expulsion features Copyright SIEP B.V. SIEP B.V.

7 Simultaneously Active, Sealing, and Leaking Normal Faults deep traps are fault dependent, but not filled to spill high SGR, CSP values (and lower columns than expected) shallow traps spill ~ at faults charge since 230 k. yr. 450 m displacement/450 k. yr. Alexander & Handschy, 1998 Depth (ft, TVDSS) Active faults seal up to 300 psi, trapping 300 MMBO (recoverable) field

8 Example of Fluid Migration along a Growth Fault: EI 330, Gulf of Mexico Pulse speed = ~140 m/yr Haney et al., 2004, 2005

9 Leakage Model for Transient Dilation fault normal dilation and traveling slip pulses during Time (during a slip event, seismic or aseismic) slip pulse Slip pulse stick-slip Anooshehpoor and Brune, PAGEOPH, 1994 Bodin et al., JGR, 1998 Main et al., Geoogy, 2000 Borcherdt et al., BSSA, 2006 Copyright SIEP B.V. SIEP B.V. fault normal dilation during stable sliding Marone et al., JGR, 1990 Beeler et al., JGR, 1996

10 Copyright SIEP B.V. SIEP B.V. ) Semi-Permanent Dilation of Gouge During Aseismic Slip md P erm eab ility (m 2 ) Permeability (m 2 ) V o lu m e tr ic F lo w R a te (Q, b b l, y ) Volumetric flow rate (Q, bbl/y E-18 x E-19 x E-20 x E-21 x E-22 x E-23 x E-02 x E-03 x E-04 x E-05 x E-06 x E-07 x E-08 x m m m m m m m m Δ Porosity (%) Δ Porosity (%) g a s o i l a. b bbl/my.01 bbl/my 140 m/yr (7 yr/km) cataclasites PFFR/smears EI330 arkosic arenites φ = 30% k = D

11 Key Points (1) Active faults still trap hydrocarbons rate of leakage vs. fill (2) Aseismic (growth) faults exhibit semi-permanent dilation, but associated permeability less than intrinsic pemeability of existing fault rock (3) Transient dilation on seismically active faults. Leakage rate f (slip rate, fault dimensions, and normal/shear pulse amplitude).

12 Path Forward A systematic study. The Basics Assemble case studies of active, trapping faults and classify according to: -observed buoyancy pressures -fault rock predictions (SGR, CSP, etc ) -slip rates & frequency -timing in relation to charge -burial history & associated rock properties The Dynamics capture the pulse! - seep data f(time) -4D seismic - monitor fault zone pore-fluid pressure and strain from logs - more???

13 Copyright SIEP B.V. SIEP B.V.