Mercia Mudstone Formation, caprock to carbon capture and storage sites: petrophysical and petrological characteristics

Transcription

1 Mercia Mudstone Formation, caprock to carbon capture and storage sites: petrophysical and petrological characteristics 1: University of Liverpool, UK 2: University of Newcastle, UK 3: FEI, Australia 4: BP Sunbury, UK Richard Worden 1 P. J. Armitage 1,4, D. R. Faulkner 1, A.C. Aplin 2, A. R. Butcher 3, A.A. Espie 4 1

2 The problem Major and growing need to understand controls on permeability of tight rocks: Caprock quality (seal capacity) for oil and gas fields Caprock quality (seal capacity) for CCS sites Shale gas Tight gas sands 2

3 Permeability of tight rocks Permeability is hard to measure on tight rocks Steady state flow (typical of core analysis) takes a long time to equilibrate Most permeability values for tight rocks are modelderived using (i) porosity and pore size distribution data or (ii) porosity and grain size distribution data All reported porosity-permeability data from sealing sedimentary rocks Clay content Yang and Aplin related mudstone permeabilityporosity relationships to the clay content Analogous to sandstones, it is feasible to predict permeability using logs 3

4 Direct measurement of permeability Steady state measurement is possible: but it takes a long time One log unit decrease in permeability requires a test x longer; measuring microdarcy ( -18 m 2 ) or nanodarcy ( -21 m 2 ) permeabilities using steady state techniques can take hours, or days. Use Transient Pulse Decay instead no need to reach steady state much faster Steady state method Pore Pressure (MPa) CO 2 Flow 11/03/20 45 MPa confining pressure Downstream pore pressure Upstream pore pressure Permeability Average permeability = m 2 (0.01 microdarcies) 8e-20 6e-20 4e-20 2e-20 1e-20 8e-21 6e-21 (80 nd) Permeability (m 2 ) 20 4e Time (Hours) 2e-21 (2 nd) 4

5 Petrophysical analysis custom built experimental apparatus Pore pressure (MPa) Upstream pore pressure Downstream pore pressure ln (p1- pf) ln (p1 - pf) Upstream pore pressure inlet Time (s) Transient pulse decay method Relatively quick test of permeability at pressure Calculated from decay of an induced pressure difference 12.6 Can alter conditions and build up a graph showing permeability versus fluid pressure (effective stress) relationships 5 Confin pressu

6 Case study: Mercia Mudstone, UK Caprock to potential CO 2 storage sites in the Lower Triassic Sherwood Sandstone Rhaetian Penarth Gp Blue Anchor Fm Cropwell Bishop Fm Norian Hollygate Dane Hills Sdst members Carnian Ladnian Anisian Scythian Edwalton Fm halite Sidmouth Mdst Fm (aka Gunthorpe, Radcliffe Fm) Sandstone Conglomerates * Sherwood Sandstone Mercia Mudstone Mercia Mdst Fm outcrop 6

7 Mercia Mudstone burial history: E Midlands, UK Mercia Mudstone Group In Willow Farm Borehole, Mercia is at about 300m TVD at present Has been to about 2500m (80 C) at maximum burial 7

8 Outcrop versus core BGS core: Willow Farm borehole Sidmouth Outcrop: weathers, loses detail and changes petrological and petrophysical characteristics. Literature tends to use outcrop Jeans 2006 (Sidmouth) Beneficial for surface civil engineering purposes Not representative of the subsurface, e.g. Jeans 2006 reports smectite (due to weathering) Seedhouse (1996) used Irish Sea core, and MICP results agree good for lateral homogeneity? 8

9 Mineralogical analysis - XRD Intensity (counts) Chlorite 001 Illite 001 Gypsum Chlorite 002 A Quartz (44 ± 12%), illite (25 ± 14%), and K-feldspar ( ± 3%) = dominant Gypsum (8%) and calcite/dolomite (6%) are highly variable Gypsum tends to be present at 15% or absent. Abundant gypsum = less illite (vice versa) Quartz K-Feldspar Gypsum Calcite Dolomite B chlorite (4%) significantly less abundant than illite no kaolinite found Intensity (counts) no swelling clay minerals (smectite) Theta (Cu K-α) 9

10 Two types of Mercia Mudstone: A 0 m Light optical microscope images q d b i f i Muddy-sandstone with illitedominated clay sitting between grains B 0 m Silty-sandstone cemented with gypsum, calcite and dolomite

11 Two types of Mercia Mudstone: Silty-sandstone cemented with gypsum, calcite and dolomite Muddy-sandstone with illite-dominated clay sitting between grains A q k g q B q q c q q C q c 200 µm Back-scattered electron microscope images q 50 m 11

12 Two types of Mercia Mudstone: A-i A-ii QEM-SCAN and conventional BSEM images 3mm Silty-sandstone cemented with gypsum, calcite and dolomite B-i B-ii Muddy-sandstone with illite-dominated clay sitting between grains BSEM images 3mm QEM-SCAN images 12

13 Petrophysical analysis - MICP Incremental / cumulative porosity (%) Pore throat radius (nm) Poresize frequency curve Cumulative porosity 13

14 Controls on Mercia mudstone caprock quality Total porosity (%) Capillary entry pressure (psi) Total clay minerals (%) A C Total clay minerals (%) Mean pore throat radius (nm) B Total clay minerals (%),, and contain abundant gypsum,, and contain abundant illite The amount of detrital clay (predominantly illite) has a primary control on porosity, mean pore throat radius and capillary entry pressure. 14

15 Permeability measured for all samples at a range of effective pressures and cycled Argon pore fluid Petrophysical analysis Vertical permeability Permeability measured in samples cored perpendicular to bedding (vertical permeability), and parallel to bedding (horizontal permeability) Permeability m m 2 = 1 nd v First compression cycle closes artefact cracks first decompression cycle responds with lower permeabilities second compression cycle same as decompression cycle Reveals real permeability and pressure sensitivity 15

16 Petrophysical -19 v -17 v analysis: vertical Permeability m 2 Permeability (m 2 ) permeability v -18 v Permeability (m 2 ) Permeability (m 2 ) v v Permeability (m 2 ) Permeability (m 2 ) m 2 = 1 nd

17 Petrophysical Analysis: horizontal permeability Permeability (m 2 ) Permeability m h h Permeability (m 2 ) Permeability (m 2 ) h h Permeability (m 2 ) -17 h Permeability (m 2 ) -16 h -21 m 2 = 1 nd

18 Permeability at 60 MPa confining pressure Permeability shows a good relationship with mean pore throat radius -16 Permeability (m2) ,, and contain abundant gypsum,, and contain abundant illite -20 Mercia vertical permeability Mercia horizontal permeability 0 00 Mean pore throat radius (nm) -21 m 2 = 1 nd 18

19 Pressure sensitivity of permeability Horizontal pressure sensitivity factor (MPa -1 ) ,, and contain abundant illite,, and contain abundant gypsum Vertical pressure sensitivity factor (MPa -1 ) Fairly low pressure sensitivity (rate of loss of permeability for increasing effective stress) Illite-rich samples have slightly higher pressure sensitivity than gypsumrich samples Illite-rich samples have slightly greater vertical than horizontal pressure sensitivity 19

20 Permeability at 60 MPa confining pressure -16 Permeability (m2) vertical permeability horizontal permeability Porosity (%) Range of permeability values relate well to range of porosities (from MICP) kv not so different to kh -21 m 2 = 1 nd 20

21 Permeability at 60 MPa confining pressure Permeability and porosity related to mineral content with most clay (illite)-rich having lower porosity and permeability than gypsum-rich samples -16 Permeability (m2) Increasin g clay (illite) content vertical permeability horizontal permeability Porosity (%),, and contain abundant gypsum,, and contain abundant illite -21 m 2 = 1 nd 21

22 Controls on Mercia mudstone caprock quality Vertical permeabiity m E E E E Total clay minerals %,, and contain abundant gypsum,, and contain abundant illite Vertical permeabiity m E E E E m 2 = 1 nd Mean pore throat radius nm (MICP data),, and contain abundant gypsum,, and contain abundant illite 22

23 Conclusions Mercia varies from poor to good caprock for CO 2 storage (as a function of sedimentary facies and mineralogy) Muddy sandstone: illite rich, lowest permeability ( 2x -20 m 2, 20 nd) Silty-sandstone: gypsum-rich, higher permeability ( 3x -18 m 2, 3 D) kh/kv ratio is low at the core plug scale (max about 2) due to broadly homogenenous textures (even in clay-rich samples) Pressure sensitivity is low but highest in the muddy sandstones Reactivity of Mercia to CO 2 will be fairly low (see later talk by Pete Armitage for contrast) 23

24 Petrophysical analysis: all values Permeability (m 2 ) Permeability m Vertical permeability Key Krechba mercia Mercia Horizontal permeability Permeability m Katsubeet al., (1991) et al., (2004) et al., (2008) Yang andaplin (2007) et al., (2002) s(1997) Cycle independent permeabilities compared with other published work Within range Low pressure sensitivity factors 2,3, and 6 gypsum 25