High-resolution seismic imaging over thickpermafrost at the 2002 Mallik drill site

D.R. Schmitt1, M. Welz1, and C.D. Rokosh1

Schmitt, D.R., Welz, M., and Rokosh, C.D., 2005: High-resolution seismic imaging over thickpermafrost at the 2002 Mallik drill site; in Scientific Results from the Mallik 2002 Gas HydrateProduction Research Well Program, Mackenzie Delta, Northwest Territories, Canada, (ed.)S.R. Dallimore and T.S. Collett; Geological Survey of Canada, Bulletin 585, 13 p.

Abstract: A short, high-resolution, two-dimensional profile and a single-fold, ‘pseudo’–three-dimen-sional, reflection-seismic volume were acquired at the 2002 Mallik drill site on Richards Island in theMackenzie Delta. The two-dimensional profile displays horizontal high-amplitude variations of limited lat-eral extent (i.e. <100 m) that are present both within and above the gas hydrate stability zone; these observa-tions are in agreement with earlier seismic surveys at the site. The current pseudo–three-dimensional surveyshowed the ‘bright spot’ and dimmed zoned variations, and confirmed lateral heterogeneity of reflectivitywithin the permafrost zone and the gas hydrate stability zone. The reflectivity variations may be due tosmall-scale changes in pore-space saturation, both within and above the gas hydrate stability zone, resultingin substantially changed compressional-wave speeds. Future work will include detailed modelling ofexpected seismic responses based on variations between pore fluid and solid.

1Institute for Geophysical Research, Department of Physics, University of Alberta, Edmonton, Alberta, Canada T6G 2J1

1

Résumé : Nous avons enregistré un profil sismique bidimensionnel à haute résolution de courteétendue, ainsi qu’un volume pseudo-tridimensionnel obtenu par réflexion sismique à couverture simple, ausite de forage Mallik 2002, sur l’île Richards, dans le delta du Mackenzie. Le profil bidimensionnel montredes variations horizontales de grande amplitude, mais d’étendue limitée (moins de 100 m), à l’intérieur etau-dessus de la zone de stabilité des hydrates de gaz. Ces observations concordent avec les résultats deslevés sismiques effectués antérieurement sur le site. Le levé pseudo-tridimensionnel montre des pointsbrillants et des zones d’atténuation, et confirme l’inégalité latérale de la réflectivité dans la zone depergélisol et la zone de stabilité des hydrates de gaz. Les irrégularités de la réflectivité pourraient être dues àdes variations à petite échelle de la saturation de l’espace interstitiel dans la zone de stabilité des hydrates degaz et au-dessus de cette zone, produisant d’importants changements des vitesses des ondes de compres-sion. Les travaux prévus pour l’avenir comprennent une modélisation détaillée des réponses sismiquesattendues selon les variations des proportions de fluides et de solides dans les pores.

INTRODUCTION

The JAPEX/JNOC/GSC et al. Mallik 3L-38, 4L-38, and5L-38 scientific wells were drilled in the Canadian Arctic(Fig. 1a) during 2002 in order to study the feasibility of meth-ane gas production from permafrost-related gas hydrate.Many research projects were initiated during this phase of theproject, including coring of the gas hydrate zones, extensivegeophysical and mud-gas logging, reservoir-evaluation test-ing, cross-well tomographic seismic studies, and verticalseismic profiling (Dallimore and Collett, 2005). This paperdescribes part of the project field program: the acquisition of ahigh spatial resolution, two-dimensional seismic profile anda single-fold, closely spaced, ‘pseudo’–three-dimensionalcoverage over the wells.

Seismic studies have been used to map the permafrostzones. Hunter and Hobson (1974) described the use of refrac-tion techniques in detecting subsea permafrost. Walker andStuart (1976) measured the seismic-interval velocities in anumber of wells drilled in the Mackenzie Delta by ImperialOil, using a ‘crystal cable’ of spaced hydrophones in con-junction with check-shot measurements. They observed highlyvariable velocities within the permafrost zones, ranging from2290 to 4120 m/s, that were substantially higher than veloci-ties of 1520 to 1980 m/s measured in deeper nonfrozen sec-tions. Hatlelid and MacDonald (1982) used the existence ofseismic refractions and reflections to infer the velocity andthickness of the permafrost.

A number of earlier seismic studies were carried out atthis site. Using reprocessed large-scale industrial surveysacquired in 1984 by Imperial Oil Ltd., Collett et al. (1999)studied a deeper, large-scale anticlinal structure that bothtraps gas and serves as a source reservoir for the methane thatconstitutes the gas hydrate. This survey was acquired withdynamite at an average common midpoint (CMP) spacing of20 m at 15 fold (the number of traces with a common midpointthat have been added together to increase the signal/noiseratio). These data were typical of exploration surveys in themid-1980s and, while they provided good regional coverage,their target zone was substantially below the permafrost andgas hydrate zones. As such, they cannot be used reliably tostudy the nearer surface stratigraphy to the bottom of the gashydrate stability zone (at a depth of about 1100 m).

Sakai (1999) and Walia et al. (1999) described moredetailed vertical-seismic-profile measurements in the 1998JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well.Their work provided in situ seismic velocities for both comp-ressional (P) and shear (S) waves, and evidence for seismicreflectivity along the profile.

In 1999, both P- and horizontal S-wave, high-resolution,two-dimensional seismic profiles (Fig. 1b) were acquiredclose to the 2002 JAPEX/JNOC/GSC et al. Mallik 5L-38 gashydrate production research well site (Hunter et al., 1999,2000; Miller et al., 2000, 2003, 2005). Their unique surveyfirst obtained high-frequency and spatial-resolution profiles,each with CMP spacings of 2.5 m at folds as great as 30 andcoverage lengths of about 1.2 km. In contrast to the regional-scale deep surveys contributed by Collett et al. (1999), they

concentrated on the gas hydrate stability zone and showedevidence, in both raw shot gathers and the final processedseismic section, that the gas hydrate zones are laterallydiscontinuous.

The work described in this paper had several purposes. First,earlier drilling, vertical seismic profiling (VSP; Sakai, 1999),and conventional (Collett et al., 1999) and high-resolution(Miller et al., 2003, 2005) seismic measurements have indicatedthat the permafrost and gas hydrate stability zones displaysome degree of lateral heterogeneity. Gas hydrate is trappedin a broad anticlinal structure composed of thick, young,unconsolidated, Tertiary deltaic sand and silt. Log evaluationof Imperial Oil Mallik L-38 and JAPEX/JNOC/GSC Mallik2L-38 shows the strata to be relatively uniform in the immedi-ate area of the Mallik wells. Recent seismic profiling acquiredin 2001 (Miller et al., 2003), however, shows horizontal vari-ations in seismic amplitudes that are likely indicative ofchanging gas-water-ice pore saturations. Vertical-seismic-profile images obtained in the Mallik 2L-38 gas hydrate eval-uation well, drilled in 1998, could also show this heterogene-ity in seismic amplitudes (Sakai, 1999; Walia et al., 1999),although these workers did not specifically make this obser-vation. The present survey was carried out in order to exam-ine the detailed structure, to the degree it may be deducedfrom high-resolution seismic imaging, with two-dimensionaland pseudo–three-dimensional coverage centred immediate-ly on the three 2002 wells (JAPEX/JNOC/GSC et al. Mallik3L-38, 4L-38, and 5L-38) and the corresponding verticalseismic profile (Milkereit et al., 2005).

Second, although the gas hydrate dissociation processitself remains an active area of research, the simple fact thatfree methane will be liberated into the pore space during thebreakdown of the gas hydrate suggests there will be a largechange in the overall seismic properties of the producing gashydrate zone. Substitution of highly compressible gas for theliquids or solids in the pore space produces a large decrease inthe seismic P-wave velocity, the bulk of the decrease actuallyoccurring at gas saturations of only a few per cent. Much ofthe essential physics of this effect is described by Gassmann’srelation (Gassmann, 1951), where the overall fluid compress-ibility takes on that of the gas, while the density remains thatof total pore saturation. Gassmann’s theory does not considerother changes in the material, particularly those that alter theframe stiffness of the rock due to damage of the grain-to-graincontacts, which could lower the velocity even further. Thisdiminished velocity leads also to a smaller elastic impedance(i.e. the product of the seismic velocity and the mass density),which is the physical property that most influences the seismicreflectivity of a given horizon. There are numerous examplesof the effect of diminished velocity, including seismic‘bright-spot’ analyses that, in many cases, provide a directindicator of free gas within a formation and the effect ofsteam injected into heavy oil reservoirs (e.g. Schmitt, 1999).Given that current knowledge of the dissociation process isimperfect, attempts to model expected seismic responses wouldbe highly speculative at best, but the likelihood that the dissoci-ation-related changes in seismic properties will be large sug-gests that time-lapse seismic measurements may be one wayto remotely study the hydrate dissociation process. The initial

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GSC Bulletin 585

high-resolution seismic measurements were also carried outto better understand some practicalities of conductingtime-lapse surveys of hydrate dissociation. Time-lapse datawere acquired, but these suffer from rig-noise problems at thesite and are still being analyzed.

This paper reports on the acquisition and processing of thefield seismic data. The resulting conventional, two-dimensionalseismic profile and the novel, single-fold, pseudo–three-dimensional seismic volume both display the lateral changesin amplitudes seen by earlier workers. Although more work isrequired to understand these variations, they are likely due tochanges in the saturation state across the short profile.

SEISMIC PROFILE SITE

Three wells at the Mallik site (i.e. Mallik 3L-38, 4L-38, and5L-38) were drilled during 2002 on Richards Island in theMackenzie Delta region of the Northwest Territories, at lati-tude 69°27′40.7″N and longitude 134°39′30.4″W. The loca-tions of these wells and the earlier Mallik L-38 and 2L-38wells are given in Table 1 and Figure 1. Since the site islocated near the shore of the Beaufort Sea, the topographyover the seismic experiment does not vary significantly and isnear 1 m above sea level. The seismic experiments were con-ducted between late February and early March 2002. Theweather conditions at the site during the recording periodswere typical for the season, with wind-chill temperaturesranging from -55°C to -20°C. Wind conditions varied sub-stantially from calm to greater than 50 km/h, which would

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D.R. Schmitt et al.

Welldesignation

Latitude Longitude Easting (m) Northing (m)

L-38 69°27'44"N 134°39'25"W2L-38 69°27'40.71"N 134°39'30.37"W 513374.39 7705661.19 3L-38 69°27'38.32"N 134°39'41.61"W 513252.500 7705586.469 4L-38 69°27'40.29"N 134°39'36.18"W 513311.248 7705647.899 5L-38 69°27'39.30"N 134°39'38.90"W 513281.874 7705617.184

Note: All eastings and northings are in North UTM zone 8 with central meridian at 135°W.

Table 1. Surveyed well locations at the Mallik drill site.

Tuktoyaktuk

MackenzieBay

Inuvik(field lab)

Aklavik

BeaufortSea

Mallik3L-, 4L- and 5L-38

2L-38L-38

Taglustagingsite

Yuko

nTe

rrito

ryN

orth

wes

t Ter

ritor

ies

137° 132°70° 70°

137° 132°68° 68°

0 25

km

a)

800 1000 1200 1400 1600 1800 2000100

200

300

400

500

600

700

800

900

1000

1100

Easting - 512000 m: UTM Zone 8

Nor

thin

g-

7705

000

m:U

TM

Zon

e8

2Dmidpointcoverage

Shot points

Recording

tent

Pseudo 3-Dmidpointcoverage Miller et al

Line 1

Miller

et alLine

2

5L

3L

4L 2L

1LReceivers

N

CMP

007

SP137

CMP

143

XL244

XL53

IL110

IL168

b)

Figure 1. a) Mackenzie Delta area, showing the location of the Mallik drill sites. The red and green lines areroads. b) Geometry of the seismic experiment at the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrateproduction research well. Surface positions of the Mallik 3L-58, 4L-58, and 5L-58 wells are shown as solidcircles. The two-dimensional midpoints for the profile extend from common midpoint number (CMP) 7 to143. Pseudo–three-dimensional coverage is indicated by the rectangle extending between in-lines (constantshot lines) 110 and 168, spaced at 3 m intervals, and between cross-lines (constant receiver lines) 53 and244, spaced at 2 m intervals. The southwest corner of the map is at UTM 8, 512700E, 7705100N.

produce white-out conditions. The data in this paper wereacquired on February 27, 2002, during the period of the lowestwind-chill recorded during the drilling program.

GEOLOGY

This section concentrates on a few structural, petrophysical,and stratigraphic features of the gas hydrate reservoirs,especially where related to the geophysical properties of therocks and therefore contributing to variations in seismic velocityand reflectivity.

Ten sedimentary sequences have been identified in the UpperCretaceous to Quaternary strata of the Beaufort-Mackenziearea (James and Baxter, 1988; Dixon et al., 1992; Dallimoreand Collett, 1999). Surficial Quaternary sediments are com-posed of modern deltaic deposits overlying older fluvial andglacial deposits to a depth of less than 100 m. Gas hydrate atMallik is trapped in a broad anticlinal structure (Collett et al.,1999) consisting of sand-dominated Tertiary strata that repre-sent a generally northward- or northeastward-progradingdeltaic facies. Three Tertiary sequences are identified on logsand in core (i.e. Iperk, Mackenzie Bay, and Kugmallit), withgas hydrate occurring in the upper Kugmallit Sequence (Dallimoreand Collett, 1999; Uchida et al., 1999) and, to a lesser degree,near the base of the lower Mackenzie Bay Sequence (depend-ing on where the top of the Kugmallit Sequence is placed). Thehydrate is encased in framework-supported, high-porosity(32–45%) sand and in matrix-supported sandy gravel with aporosity of 23 to 29%. The degree of consolidation of the sed-iments is variable, but they are generally weakly consoli-dated, hence affecting P- and S-wave velocities throughvariations in bulk framework moduli. Shale content, calcu-lated from well logs, is generally less than 10% in the poorlyconsolidated, quartz-rich (approx. 90%) reservoir sand. Logevaluation shows that at least six coal beds, approximately 1to 3 m thick, are present in the approximately 580 m thickKugmallit Sequence (Miyairi et al., 1999, Fig. 5).

According to well-log evaluation of Mallik 2L-38, approx-imately 111 m of net gas hydrate pay occur between 810.1and 1102.3 m below surface, comprising four gas-bearingsequences that range in thickness from about 20 to 35 m, eachresting on water-saturated sediments (Dallimore and Collett,1999). The clathrate is generally fine grained (<2 mm) andfills intergranular pores or coats mineral grains (Uchida et al.,1999), along with rare thin veins (1–2 mm) and clasts or nod-ules (up to 0.5 mm, more rarely 2 mm). Gas hydrate satura-tion has been calculated from well logs at more than 60% inthe gas-hydrate-bearing zones and peaks at slightly more than90% (Miyairi et al., 1999; Collett et al., 1999; Dallimore etal., 1999). Free hydrocarbons have also been identified onwell logs immediately below the calculated gas hydratestability zone in one thin sand between 1108.4 and 1109.8 m.

The base of the permafrost zone at the Mallik site is at a depthof approximately 640 m within the middle of the Mackenzie BaySequence and dips to the northeast at about 4 m/km (Majorowiczand Smith, 1999; Collett et al., 1999). Miller et al. (2003)observed no clear seismic reflection at the base of the permafrost,

where velocity dropped from 4200 to 1500 m/s, and sug-gested that the permafrost base is gradational over about50 ms. Miller et al. (2003) also observed a strong reflection inthe permafrost zone, at about 200 ms two-way travel time,that occurs at about the position of the disconformable con-tact between the Iperk and Mackenzie Bay sequences.

The calculated depth to the base of the gas hydrate stabil-ity zone is about 1100 m at the Mallik site. The gas hydratebase dips steeply (at 35 to 50 m/km) from the southwesttoward the Mallik 2L-38 well site and, toward the northeast,exhibits a shallower slope of about 10 m/km (Judge andMajorowicz, 1992; Dallimore and Collett, 1999, Fig. 5).Detecting this dip over the small coverage of the current pro-files would be difficult. High-amplitude reflections within thegas hydrate zone (Miller et al., 2003) were observed as later-ally discontinuous. The breadth of the reflectors within themain zone of gas hydrate concentration is generally a fewhundred metres, with the reflectors reappearing laterally after afew tens of metres. Miller et al. (2003) suggested that the lackof lateral reflection continuity might relate to variations in gashydrate concentration or changes in clay content rather than torock types. Nevertheless, laterally discontinuous high-amplitudereflectors are also seen in the Miller et al. (2003) data and inthe data set from this study above the zone of gas hydrate con-centration. Lateral continuity of reflectors is perhaps notexpected in this area owing to laterally complex geology atthe scale of a few hundred metres. For example, Collett et al.(1999) proposed that bottom-simulating reflectors (BSR), asobserved in seismic sections over marine gas hydrate accu-mulations, should not be expected in the Mackenzie Delta. Inmarine settings near the continental-shelf edge, gas hydrate isfound in laterally continuous and vertically homogeneous siltand clay, whereas gas hydrate accumulations in the MackenzieDelta are located in “complexly interbedded sandstone andshale sequences” (Collett et al., 1999, p. 370), with thehydrate dominantly accumulating in high-porosity sand. Hence,the geometry or architecture of the geological environmentsnear the Mallik site (i.e. fluviodeltaic) may not lend itself tocontinuous reflectors such as a BSR, either within a sequenceor at the base of the gas hydrate. According to Hill et al. (2001),submarine distributary channels in the modern MackenzieDelta are up to approximately 10 m thick and a few hundredmetres wide, while the seismic reflections in the Miller et al.(2003) Tertiary sequences similarly span a maximum of afew hundred metres.

FIELD EXPERIMENTS

Geometry

The seismic experiment itself was constrained by a number ofenvironmental and physical factors that limited operation ofthe seismic source to the ice road leading directly to theMallik drill site. Therefore, a ‘T’ receiver layout was employed(Fig. 1b) in order to obtain both a two-dimensional profileand an unconventional, single-fold, three-dimensional vol-ume. The shot-line trends east-northeast, pointing toward themain Mallik 5L-38 borehole. The extent of the shot line wasconstrained to the west by the camp itself and to the east by

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GSC Bulletin 585

the geometry of the ice road and the energy of the seismicsource. The ‘T’ array was laid out on the tundra to the west ofthe drill site such that the Mallik 3L-58, 4L-58, and 5L-58 wellswould fall at the source-receiver midpoints. The array wasplaced using differential GPS (DGPS) positioning after thesource line had been surveyed, in order that the two-dimensionalprofile would be centred near the Mallik 5L-38 well. The 61common shot gathers along the base of the ‘T’ that was usedto provide the two-dimensional profile had offsets rangingfrom 510 m to 1070 m, the offsets being controlled by theaccess to the Mallik site (as noted above).

The University of Alberta IVI minivibrator source, con-sisting of a high-frequency vibrator of 6000 pounds forcemounted on a weighted 3-ton truck (Fig. 2), was used to pro-vide seismic energy on February 27, 2002. The source oper-ated with linear sweeps, of 14 seconds duration, from 12 Hzto 180 Hz at 5500 pounds force; the source vibration wasrepeated eight times at each location. The force level of thevibrator plate remained uniform over the entire sweep, indi-cating good coupling with the ice road. A 6 m source spacingwas used, with each of the final 61 shotpoints being locatedwith DGPS.

The two-dimensional line was acquired using 48 channelsalong the stem of the ‘T’, and the resulting subsurface cover-age extends for 266.2 m, centred on the Mallik 5L-38 well,with 137 CMP traces at a 2 m spacing, the fold varying from1 to 36 (Fig. 3). The single-fold, pseudo–three-dimensionalcoverage was obtained from 192 channels laid out along thetop of the ‘T’. Standard OYO® Instruments 14 Hz geophonesingles were spaced at 4 m intervals along both the stem andtop of the ‘T’; each of the 240 receiver locations was deter-mined using DGPS. This geometry results in a 2 m CMPspacing for the two-dimensional line and for the in-line (orshot-line) trace spacings for the pseudo–three-dimensionalvolume. Placement of the receivers involved cutting downthrough the snow to the surface, which consisted mainly ofice at the top of frozen lakes but less so over small islands, anddrilling a small hole in the surface into which the receivercould be placed (Fig. 4). The small pit around the geophonewas quickly refilled with blowing snow; the snow providingsome degree of isolation from airborne noise.

Seismic traces were acquired using the University ofAlberta 240-channel semidistributed system that consists often 24-channel field boxes (Geode™ system manufacturedby Geometrics Ltd.) linked via a field intranet to the controland storage computer. The computer and operators werehoused in an offsite, heated, double-walled tent near the geo-phone array. Correlation of the radio-transmitted sweep occurredon the field boxes after each sweep and prior to vertical stack-ing. The filtered ground motion, as measured by accelerome-ters on the vibrator plate and provided directly by the IVIvibrator control system, was used as the sweep. Excellentcoupling of the plate to the ice road was achieved, as indicatedby monitoring of the force for each shot. Each field boxrequires its own battery, and battery life in the extreme coldhad been an important concern prior to the field measure-ments. Nevertheless, the system appeared to run efficientlyand no recording time was lost due to low battery voltages.

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D.R. Schmitt et al.

Figure 2. University of Alberta IVI Minivibrator seismicsource on the ice road leading to the Mallik camp.GSC 2004-143

20 40 60 80 100 120 1400

5

10

15

20

25

30

35

Common midpoint number

Fol

d

Figure 3. Plot of fold versus common midpoint for two-dimensionalprofile, 2002 Mallik drill site.

Figure 4. Typical pit on ice for placement of geophones, 2002Mallik drill site. The pit is about 60 cm square and 50 cm deep,and the arrow points to a geophone head that is about 6 cm by4 cm. GSC 2004-144

Data processing

This study focuses on reflected seismic energy and, as such,both rig-produced noise and source-generated Rayleigh sur-face waves contaminated the records. An example of a rawseismic record (Fig. 5, left panel) shows that both the rig noiseand the dispersive source-generated surface-wave move outat speeds of less than 2500 m/s. These nearly parallel arrivalssuggest the rig noise is transferred to the receivers as a surfacewave and not through the air. The rig noise is most evidentprior to the arrival of the direct wave, which moves out at avelocity near 4000 m/s, as can be traced from 200 to 260 msover the range from trace 1 to trace 48 in Figure 5. For the off-sets associated with shot 137, the Rayleigh wave train, whichwas among the strongest arrivals, clearly interfered with thedesired reflected energy at times from 450 to 550 ms on trace 1.The speeds of both the Rayleigh and the direct waves wererelatively high due to their transmission through the frozenground. A two-dimensional f-k filter was applied to each ofthe shot gathers in order to attenuate both the rig noise and theRayleigh wave; the filtered version of the raw shot gathers(Fig. 5, middle and right panels) indicates that much but notall of this undesired energy was removed.

Although velocity analysis was carried out on these filtereddata, the most successful velocity model was developed usingthe interval velocities derived from the vertical seismic pro-filing observations obtained in the Mallik 4L-38 well byMilkereit et al. (2003). The normal velocity analyses weredifficult because of the relatively short range of shot-receiveroffsets available and the limited lateral extent of the events.This problem was compounded by the high near-surfacevelocities of the permafrost, which resulted in only smallmoveout over a given CMP gather and therefore larger uncer-tainty in the stacking velocity. The topmost measurement intheir two-way travel time to depth curve (Fig. 6) was from250 m depth, and the times extrapolated back reasonably tothe surface. The trend of the two-way times derived from theearlier measurements below a depth of 500 m by Walia et al.(1999) in the 1998 Mallik 2L-38 drillhole agree well but aresystematically shifted to shorter times by 75 ms. Both of thevertical seismic travel-time curves, however, show a notice-able change in slope consistent with higher interval velocitiesat depths shallower than 600 m, and are in good agreementwith inferred permafrost thicknesses.

The trend with depth of the near-vertical VSP intervalvelocities (Fig. 7) agrees well with the P-wave sonic-loginformation obtained during the logging program at the Mallik

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GSC Bulletin 585

A) Raw B) Filtered C) Filtered/AGC

45

757 777 797 817 837 857 877 897

50 55 60 65 70 75 80 85

737

48

737 777 797 817 837 857 877 897

53 58 63 69 74 79 84 90

737

48

757 777 797 817 837 857 877 897

53 58 63 69 74 79 84 90

Offset

CMP

200

400

600

800

1000

Tim

e(M

s)

737

1: SHOT_POINT_NO 1-137.0[48] 1: SHOT_POINT_NO 1-137.0[48] 1: SHOT_POINT_NO 1-137.0[48]

Figure 5. A 1200 ms long, two-dimensional shot-gather record (with root-mean-square normalization only)produced by shotpoint 137 near the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production researchwell: A) as observed (‘Raw’); B) after debiasing and application of an f-k filter (‘Filtered’); and C) afterapplication of the same f-k filter and debiasing but with a 300 ms automatic gain control applied (‘Filtered/AGC’).

7

D.R. Schmitt et al.

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

200

300

400

500

600

700

800

900

1000

1100

1200

Checkshot two-way travel time (s)

Dep

thbe

low

kel

lybu

shin

g(m

)

Mac

Ken

zie

Bay

Iper

kK

ugm

alik

Per

maf

rost

?Figure 6. Plot of depth versus two-way travel times asobtained from first-arrival picking of the near-source, offset,vertical seismic profile obtained in the JAPEX/JNOC/GSCet al. Mallik 4L-38 well (data provided by Milkereit et al.,2005). Thicknesses of the various geological formations and ofthe ice-bonded permafrost are shown.

0 1000 2000 3000 4000 5000 6000

0

200

400

600

800

1000

1200

Velocity (m/s)D

epth

belo

wke

llybu

shin

g(m

)

P-sonic

S-sonic

P-VSP P-stacking

Figure 7. Plots of vertical seismic profiling (VSP) and log-compressional, log-shear, and calculated root-mean-square(RMS) velocities versus depth for the JAPEX/JNOC/GSCet al. Mallik 4L-38 and 5L-38 wells (data provided byMilkereit et al., 2005).

NE SW

Kug

mal

it

100 m

Mallik5L-38

CMPYC

CMPXC

200

400

600

800

1000

Tim

e(m

s)

7705797

513294

7705790 7705781 7705773 7705766 7705758

513257 513220 513183 513146 513108

Iper

kIp

erk

Mac

Ken

zie

Bay

Mac

Ken

zie

Bay

Per

maf

rost

Per

maf

rost

Figure 8. Two-dimensional seismic profile passing near the JAPEX/JNOC/GSC et al. Mallik 5L-38 well(see Fig. 1b for location). Common midpoint spacing was 2 m. A 300 ms window automatic gain control wasapplied to this section for display. The colour bar ranges from black to red, corresponding to positiveand negative amplitudes, respectively. Abbreviations: CMPYC, common-midpoint northing; CMPXC,common-midpoint easting.

5L-38 well. These velocities were used to directly calculatethe root-mean-square (RMS) velocity versus two-way verti-cal time function that was necessary to apply the normalmoveout correction to the traces in order to eliminate theeffects of offset. This RMS function atypically decreasedwith depth (or two-way time) due to the very high velocitiesencountered in the uppermost permafrost layer. It was foundduring processing, however, that this velocity function neededto be adjusted to slightly higher velocities, by about 10%, inorder to properly flatten events. No special accommodationwas made in this study for the influence of offset with aniso-tropy. This anisotropy might be a consequence of the velocityanisotropy also observed by Milkereit et al. (2005) in theirmore oblique offset VSP measurements. The source of theanisotropy is currently unknown. Alternatively, the discrep-ancy may arise from use here of the standard hyperbolicreflection moveout assumption. Poley and Lawton (1991)modelled the ray paths and travel times expected for a numberof marine surveys over permafrost and concluded that anonhyperbolic normal moveout correction may be requiredbeneath the ice-bearing permafrost. Whether this problemwould apply to zones within the permafrost needs to beinvestigated.

Aside from obtaining the velocity function from amodification of the seismic band VSP interval velocities, thetwo-dimensional profile was processed in a standard fashion.The 4 m receiver spacing enforced a 2 m CMP spacing; thiswas retained and accounts for minor crooked-line CMP binningusing the seismic- processing software Vista™. The processingstream is outlined in Table 2. The resulting two-dimensionalprofile is shown in Figure 8.

The pseudo–three-dimensional volume is unique in that itis single fold, with the source shooting broadside into the topof the ‘T’ array with 196 geophones. There is minimal pro-cessing of these single-fold data (Fig. 8). Again, to amelioratethe strong Rayleigh wave and rig noise, the data were resortedinto common receiver gathers (CRG). The moveout of boththe noise and the Rayleigh wave are apparent in this projec-tion of the data, and an f-k filter was applied to the CRG after

the normal moveout (NMO) correction had been applied.This had the effect of further separating the noise from thedesired reflections in the f-k domain, allowing for a cleanerfilter. This data volume was then saved in an appropriateformat for transfer to seismic-data-interpretation software(Kingdom Suite™). A series of cutaway views of this seismicvolume is shown in Figure 9, and the corresponding movie isincluded on the accompanying CD-ROM (Schmitt, 2005).

RESULTS AND DISCUSSION

Localization of seismic energy

The unprocessed shot gathers of Figure 6 show a rapid decayin signal amplitude from the surface, indicating that a largeportion of the seismic energy is localized within the perma-frost zone. This is also apparent in the amplitude-envelopeattribute of the ungained two-dimensional profile (Fig. 10).In general, the amplitude remains strong until approximately400 ms, which corresponds closely to the inferred bottom ofthe ice-bonded permafrost zone. This effect was predicted bymodelling carried out by Milkereit et al. (2005), and is prob-lematic in the sense that the seismic reflections expected fromthe gas hydrate zone will be of relatively lower amplitude.

Lateral amplitude variations

A more interesting observation in Figures 8 and 10 is the lat-eral variations in seismic amplitude (i.e. a number of ‘brightspots’ appearing). At face value, these variations occur alonga given horizon and appear, in general, to extend no more than100 m. These bright zones appear at all times in the section;it must be remembered that the profile shown in Figure 8 hashad an AGC gain applied that tends to weaken the events nearthe surface due to the very strong early events immediatelybelow 100 ms. Some examples of these zones include one at300 m to the left of the centre of the image, and another at 550 msimmediately to the left of the Mallik 5L-38 well. Some of thesebright spots are likely artifacts of surface-wave contamination;for example, the bright reverberations beginning at 500 ms atthe northeast end and at 700 ms at the southwest end of theprofile could be due to stacking of remaining surface-waveenergy where the fold is relatively low. Nevertheless, imperfectsurface-wave removal cannot explain shallower events.

Similar characteristics are seen in the single-fold pseudo–three-dimensional seismic volume. Figure 9 displays a seriesof cutaway views, with the in-line face progressively movingto the southwest with in-line number. Although best viewedin the movie on the accompanying CD-ROM, one brightanomaly is seen in Figure 9 near 300 ms in panel 120; thisanomaly appears wider in panel 130 but shifts to the left(southeast) by panel 150. Other examples of short-range(<100 m extent) amplitude anomalies are also present. Theblooming and decaying of these amplitude anomalies aremuch more apparent in animated visualizations, which unfor-tunately cannot be provided here. These data have been sub-ject to minimal processing aside from the application of anNMO correction and of the f-k filter to attenuate noise alongthe cross-line (common receiver) direction. Although the f-k

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GSC Bulletin 585

Two-dimensional profile Pseudo–three-dimensional volume Acquisition (SEG2) Broadside acquisition (SEG2) Add geometry Add geometry to headers Convert to SEGY Convert to SEGY Field static corrections Field static corrections De-bias De-bias RMS mean RMS mean f-k filter shot gathers f-k filter on common receiver gathers NMO correction NMO correction RMS mean RMS mean CMP stacking Save SEGY RMS mean Display volume Display Abbreviations: f-k, frequency (f)–wavenumber (k); NMO, normal moveout; RMS, root mean square; SEG2, SEGY, digital data acquisition formats approved by the Society of Exploration Geophysicists (SEG) Technical Standards Committee; CMP, common midpoint.

Table 2. Processing streams for two-dimensional profileand single-fold pseudo–three-dimensional volume.

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110 120

130 140

150 160

XL 053

XL 148

XL 244

Figure 9. Series of pseudo–three-dimensional chair-cut views down into the single-fold seismic volume, lookingfrom southeast to northwest (see Fig. 1b for additional orientation information) near the JAPEX/JNOC/GSCet al. Mallik 5L-38 gas hydrate production research well. In-lines (shot lines) 110 to 168 trend to the northwestat 2 m spacings and cross-lines (receivers) 53 to 244 trend to the southwest at 3 m spacings. The volume is1 second thick. Thin white lines provide geographic reference to north-south, east-west, and time axes. Theeast-west axis has been stretched relative to the north-south axis in order to make the features more visible. Ineach frame, the in-lines are moved progressively to the southwest, with in-lines 110, 120, 130, 140, 150, and160 shown. The first panel shows cross-lines 53, 148, and 244. The black arrows point to the bright anomalymentioned in the text.

filter can produce some smearing along the cross-line direc-tion, as is apparent in the smoothed appearance of the cross-lines in Figure 9, it cannot influence adjacent traces in thein-line (common shot) frames; each in-line trace is independ-ent of the next, particularly since each was also acquiredusing single geophone groups that are essentially point detec-tors. Furthermore, these data rely on close proximity of detec-tors and midpoints to highlight continuity and to reduce thedegree of smearing that occurs during CMP stacking, not onstacking of numerous corrected traces. The continuity of thebright spots from adjacent but independent traces furthersuggests that these amplitude anomalies are not acquisition orprocessing artifacts.

Although it is tempting to interpret these bright spots asactual geological features, there are some physical constraintsthat must be accounted for. One issue that must be consideredis the resolution of the seismic image, both laterally and tem-porally. Conventional analyses consider lateral resolution tobe measured by the first Fresnel zone, and the temporal reso-lution to be measured by the Rayleigh criterion. Taken at facevalue, the former suggests that the smallest resolvable featurewith lateral dimensions will have dimensions of 2rF, where rFis the radius of the first Fresnel zone, approximated by,

r1

2zF ≈ • •λ

where z is the depth and λ is the predominant wavelength. Anestimate of the total width of the Fresnel zone, assuming apredominant frequency of 50 Hz (Fig. 11) and using the aver-age velocity to a given depth as determined from the verticalseismic profiling, shows that the width of the Fresnel zoneover the depth ranges of interest is greater than 100 m. TheRayleigh-criterion (λ/4) vertical resolution, calculated using

the same predominant frequency and the VSP intervalvelocities of Figure 3, remains relatively uniform, varyingfrom 10 to 14 m in thickness. At face value, both of these criteriasuggest that resolution of features smaller than this would be dif-ficult. This may be the case, but it must be realized that the detec-tion of an anomaly is not the same as being able to resolve it in astructural sense. The amplitude anomalies seen in Figures 8 to10 are smaller than the purported resolution limit. The resolutionlimits as calculated do not, however, consider the effect ofamplitude variations on thin beds (for further discussion, seeSchmitt 1999), and it is these changes in amplitude that are likelybeing detected in the data. That said, it is likely that what isobserved is a product of nonspecular scattering of the seismicwavefield as it impinges on features with dimensions at or nearthe seismic wavelengths, so the observed anomalies are likelydue, in part, to diffractions. Without further study, it would bedangerous for the interpreter to obtain measures of the size of theanomalous features based on their face-value dimensions withineither the two-dimensional profile or the pseudo–three-dimen-sional volume.

Interpretation

Although a conclusive interpretation of the seismic observa-tions and, in particular, the amplitude anomalies cannot beprovided at this point, it remains interesting to speculate onwhat their source may be. Since the amplitude anomaliesmust be caused by changes in the elastic properties of thematerial, these data may lead to a better understanding of thestructure of such thick permafrost. Permafrost is known tocontain talik (thaw zones), cryopeg (zones of saline waters inwhich the salinity has been enhanced by freezing of the adja-cent regions), and free gas. Numerous studies, both experi-mental and theoretical, have demonstrated large changes in

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GSC Bulletin 585

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seismic velocity based on saturation. The seminal study byTimur (1968) of the freezing of saline waters in the porespaces of rocks illustrates the importance of freezing on theoverall compressional-wave velocities in porous sandstone. Thevelocity of dry sandstone changed little with temperature overthe range from +26oC to -36oC, whereas velocities in thesame rocks saturated with distilled water increased by 32.9%in a Berea sandstone (porosity of 18.1%) and nearly 51.2% ina more porous Boise sandstone (porosity of 26.4%). Theseobservations have been confirmed by numerous other workers(e.g. King, 1977). Conversely, substitution of gas for waterinto the pore space, as discussed earlier, has an opposite butequally significant effect in weakly consolidated porous rocks.One early example of this effect was given by Domenico(1977), who showed the compressional-wave velocity of awater-saturated Ottawa sand (porosity of approx. 38.0%)under a confining pressure near 7 MPa decreased by 45.1%

upon replacement of the water with gas. The elastic proper-ties of a given porous formation can therefore vary dramati-cally based on whether a few percentage points of ice, unfrozenwater, or free gas are contained in the pore space; variation inthe saturation state of the materials is one possible explana-tion for such strong lateral changes in the seismic reflectivity.Walker and Stuart (1976) also suggested that shale unitswithin the permafrost have lower velocities than sand, basedon an assumption that less permeable shale does not freeze,but this idea needs further testing.

CONCLUSIONS

A high spatial resolution, two-dimensional, seismic-reflectionprofile (250 m in length) and a single-fold, pseudo three-dimensional seismic volume were acquired, centred over theMallik 3L-58, 4L-58, and 5L-58 wells. The common mid-point spacing of the data sets is 2 m for the two-dimensionalprofile traces and a 2 m by 3 m binning for the single-foldtraces that produced the pseudo three-dimensional volume.Good lateral continuity is seen in the data sets, although bothdisplay lateral variations in reflection strength over distancesof less than 100 m. These observations agree well with theearlier detailed seismic surveys described by Hunter et al.(1999, 2000) and Miller et al. (2003), and may be indicativeof the variable velocities observed by Walter and Stuart (1976)using well-bore seismic surveys. Issues related to the resolu-tion of the seismic experiment, as well as a lack of knowledgeof the detailed structure of the permafrost and gas hydrate sta-bility regimes, preclude a detailed interpretation of theseamplitude variations at present. Nevertheless, it is likely thatreflectivity variations result from small-scale changes in sat-uration, given that porous sections of these zones can be satu-rated concomitantly with ice, unfrozen water, and free gas, asat Mallik, and that these differing saturations result in sub-stantially changed compressional-wave speeds. Future workwill include detailed modelling of expected seismic responsesbased on variations in the proportions of pore fluid and solid.

ACKNOWLEDGMENTS

This work could not have occurred without the assistance infield deployment of M. Lazorek and L. Tober, and infrastructuralassistance at the field site by M. Riedel. Additional field assis-tance was provided by D. Banerjee, B. Milkereit, E. Adam,G. Pratt, and K. Bauer. The support of the staff, both at theMallik drill site and in Inuvik, was also critical to the success ofthe project. The authors acknowledge the international partner-ship that undertook the Mallik 2002 Gas Hydrate ProductionResearch Well Program: Geological Survey of Canada (GSC),Japan National Oil Corporation (JNOC), GeoForschungsZentrumPotsdam (GFZ), United States Geological Survey (USGS),India Ministry of Petroleum and Natural Gas (MOPNG),BP-ChevronTexaco-Burlington joint venture parties, andUnited States Department of Energy (USDOE). The programreceived financial support from the International ContinentalScientific Drilling Program (ICDP). The authors also acknowl-edge Seismic Image Software Ltd. for access to the Vista™

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Figure 11. a) Width of lateral resolution versus depth, asdetermined by the conventional first Fresnel zone /4 criteria,using average velocities to depth and a predominant frequencyof 50 Hz. b) Vertical resolution versus depth, as determined bythe Rayleigh /4 criteria, using interval velocities determined byvertical seismic profiling and a predominant frequency of 50 Hz.

seismic-data-processing program. This work was primarilyfunded by the senior author’s NSERC discovery grant and theCanada Research Chairs program. The manuscript was improvedthrough the careful reviews of S. Pullan and an anonymousreviewer, and the professional editing of Bob Davie.

REFERENCES

Collett, T.S., Lee, M.W., Dallimore, S.R., and Agena, W.F.1999: Seismic- and well-log-inferred gas hydrate accumulations on Richards

Island; in Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38Gas Hydrate Research Well, Mackenzie Delta, Northwest Territories,Canada, (ed.) S.R. Dallimore, T. Uchida, and T.S. Collett; GeologicalSurvey of Canada, Bulletin 544, p. 357–376.

Dallimore, S.R. and Collett, T.S.1999: Regional gas hydrate occurrences, permafrost conditions, and Cenozoic

geology, Mackenzie Delta area; in Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate Research Well, MackenzieDelta, Northwest Territories, Canada, (ed.) S.R. Dallimore, T. Uchida,andT.S. Collett; Geological Surveyof Canada, Bulletin544, p. 31–43.

2005: Summary and implications of the Mallik 2002 Gas Hydrate Produc-tion Research Well Program; in Scientific Results from the Mallik2002 Gas Hydrate Production Research Well Program, MackenzieDelta, Northwest Territories, Canada, (ed.) S.R. Dallimore andT.S. Collett; Geological Survey of Canada, Bulletin 585.

Dallimore, S.R., Collett, T.S., and Uchida, T.1999: Overview of science program, JAPEX/JNOC/GSC Mallik 2L-38 gas

hydrate research well; in Scientific Results from JAPEX/JNOC/GSCMallik 2L-38 Gas Hydrate Research Well, Mackenzie Delta, NorthwestTerritories, Canada, (ed.) S.R. Dallimore, T. Uchida, and T.S. Collett;Geological Survey of Canada, Bulletin 544, p. 11–17.

Dixon, J., Dietrich, J.R., and McNeil, D.H.1992: Upper Cretaceous to Pleistocene sequence stratigraphy of the

Beaufort-Mackenzie and Banks Island areas, northwest Canada;Geological Survey of Canada, Bulletin 407, 90 p.

Domenico, S.N.1977: Elastic properties of unconsolidated porous sand reservoirs; Geo-

physics, v. 42, p. 1339–1368.Gassmann, F.1951: Elasticity of porous media (Uber die Elastizitat poroser Medien);

Vierteljahreszeitschrift der Naturforschenden Gessellschaft in Zurich,v. 96, p. 1–23 (translation).

Hatlelid, W.G. and MacDonald, J.R.1982: Permafrost determination by seismic velocity analysis; Canadian

Journal of Exploration Geophysics, v. 18, p. 14–22.Hill, P.R., Lewis, P., Demarais, S., Kauppaymuthoo, V., and Rais, H.2001: The Mackenzie Delta: sedimentary processes and facies of a high-latitude,

fine-grained delta; Sedimentology, v. 48, p. 1047–1078.Hunter, J.A. and Hobson, G.D.1974: Seismic refraction method of detecting sub-seabottom permafrost; in

The Coast and Shelf of the Beaufort Sea, (ed.) J.C. Reed and J.E. Sater;Arctic Institute of North America, Arlington, Virginia, p. 401–416.

Hunter, J.A., Miller, R.D., Doll, W.E., Carr, B.J., Burns, R.A., Good, R.L.,Laflen, D.R., and Douma, M.2000: Feasibility of high resolution P- and S-wave seismic reflection to detect

methane hydrate; Geological Surveyof Canada, OpenFile 3850, 45p.Hunter, J.A., Miller, R.D., Doll, W.E., Carr, B.J., Burns, R.A., Good, R.L.,Laflen, D.R., Douma, M., and Riedel, M.1999: Feasibility of high resolution P- and S-wave seismic reflection to

detect methane hydrate (abstract); Society of Exploration Geophys-icists, Sixty-Ninth Annual Meeting, Oct. 31–Nov. 5, 1999, Houston,Texas, Technical Program Expanded Abstracts, p. 445–448.

James, D.P. and Baxter, A.J.1988: Stratigraphy and sedimentology of the Kugmallit Formation, Nipterk

structure: Beaufort-Mackenzie Basin, Canada; in Sequences, Stratig-raphy and Sedimentology: Surface and Subsurface, (ed.) D.P. Jamesand D.A. Leckie; Canadian Society of Petroleum Geologists, Memoir15, p. 117–126.

Judge, A.S. and Majorowicz, J.1992: Geothermal conditions forgas hydrate stability in the Beaufort-Mackenzie

area: the global change aspect; Global and Planetary Change, v. 6,p. 251–263.

King, M.S.1977: Acoustic velocities and electrical-properties of frozen sandstones and

shales; Canadian Journal of Earth Sciences, v. 14, p. 1004–1013.Majorowicz, J. and Smith, S.1999: Review of ground temperatures in the Mallik field area: a constraint to

the methane hydrate stability; in Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate Research Well, MackenzieDelta, Northwest Territories, Canada, (ed.) S.R. Dallimore, T. Uchida,andT.S. Collett; Geological Surveyof Canada, Bulletin544, p. 45–56.

Milkereit, B., Adam, A., Li, Z., Qian, W., Bohlen, T., Banerjee, D.,and Schmitt, D.R.2005: Multi-offset vertical seismic profiling: an experiment to assess

petrophysical-scale parameters at the JAPEX/JNOC/GSC et al.Mallik 5L-38 gas hydrate production research well; in ScientificResults from the Mallik 2002 Gas Hydrate Production ResearchWell Program, Mackenzie Delta, Northwest Territories, Canada,(ed.) S.R. Dallimore and T.S. Collett; Geological Survey of Canada,Bulletin 585.

Miller, R.D., Hunter, J.A., Doll, W.E., Carr, B.J., Burns, R.A., Good, R.L.,Laflen, D.R., and Douma, M.2000: Imaging permafrost with shallow P- and S-wave reflection (abstract);

Society of Exploration Geophysicists, Seventieth Annual Meeting,August 6–11, 2000, Calgary, Alberta, Technical Program ExpandedAbstracts, p. 1339–1343.

Miller, R.D., Hunter, J.A., Doll, W.E., Carr, B.J., and Collett, T.S.2005: High-resolution seismic imaging of the gas hydrate stability zone at

the Mallik 5L-38 research site; in Scientific Results from the Mallik2002 Gas Hydrate Production Research Well Program, MackenzieDelta, Northwest Territories, Canada, (ed.) S.R. Dallimore and T.S.Collett; Geological Survey of Canada, Bulletin 585.

Miller, R.D., Hunter, J.A., Doll, W.E., Carr, B.J., Good, R.L.,Burns, R.A., Laflen, D.R., and Douma, M.2003: High-resolution seismic imaging of the hydrate stability zone: Mallik,

Canada (poster presented at the American Association of PetroleumGeologists, Annual Meeting, May 2003, Salt Lake City, Utah);United States Geological Survey, Open File Report 2003-36.

Miyairi, M., Akihisa, K., Uchida, T., Collett, T.S., and Dallimore, S.R.1999: Well-log interpretation of gas-hydrate-bearing formations in the

JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well; inScientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas HydrateResearch Well, Mackenzie Delta, Northwest Territories, Canada,(ed.) S.R. Dallimore, T. Uchida, and T.S. Collett; Geological Surveyof Canada, Bulletin 544, p. 281–294.

Poley, D.F. and Lawton, D.C.1991: A model study of multichannel reflection seismic imaging over

shallow permafrost in the Beaufort Sea continental shelf; CanadianJournal of Exploration Geophysics, v. 27, p. 34–42.

Sakai, A.1999: Velocity analysis of vertical seismic profile (VSP) survey at JAPEX/

JNOC/GSC Mallik 2L-38 gas hydrate research well, and related prob-lems for estimating gas hydrate concentration; in Scientific Results fromJAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate Research Well, Macken-zie Delta, Northwest Territories, Canada, (ed.) S.R. Dallimore, T. Uchida,andT.S.Collett;GeologicalSurveyofCanada,Bulletin544,p.341–355.

Schmitt, D.R.1999: Seismic attributes for monitoring of a shallow heated heavy oil res-

ervoir: a case study; Geophysics, v. 65, p. 368–377.2005: Pseudo-3D seismic volume movie; in Mallik 2002 Gas Hydrate

Production Research Well Program, Mackenzie Delta, NorthwestTerritories: well data and interactive data viewer, (comp.) S.R. Dallimore,B.E. Medioli, R.R. Laframboise and D. Giroux; Appendix A inScientific Results from the Mallik 2002 Gas Hydrate ProductionResearch Well Program, Mackenzie Delta, Northwest Territories,Canada (ed.) S.R. Dallimore and T.S. Collett; Geological Survey ofCanada, Bulletin 585.

Timur, A.1968: Velocity of compressional waves in porous media at permafrost

temperatures; Geophysics, v. 33, p. 584–595.Uchida, T., Matsumoto, R., Waseda, A., Okui, T., Yamada, K.,Uchida, T., Okada, S., and Takano, O.1999: Summary of physicochemical properties of natural gas hydrate and

associated gas-hydrate-bearing sediments, JAPEX/JNOC/GSCMallik 2L-38 gas hydrate research well, by the Japanese researchconsortium; in Scientific Results from JAPEX/JNOC/GSC Mallik2L-38 Gas Hydrate Research Well, Mackenzie Delta, NorthwestTerritories, Canada, (ed.) S.R. Dallimore, T. Uchida, and T.S. Collett;Geological Survey of Canada, Bulletin 544, p. 205–228.

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Walia, R., Mi, Y., Hyndman, R.D., and Sakaim, A.1999: Vertical seismic profile (VSP) in the JAPEX/JNOC/GSC Mallik 2L-38

gas hydrate research well; in Scientific Results from JAPEX/JNOC/GSCMallik 2L-38 Gas Hydrate Research Well, Mackenzie Delta, NorthwestTerritories, Canada, (ed.) S.R. Dallimore, T. Uchida, and T.S. Collett;Geological Survey of Canada, Bulletin 544, p. 341–356.

Walker, J.H.D. and Stuart, A.J.1976: Permafrost investigations by crystal cable surveys, Mackenzie Delta,

N.W.T.; CanadianJournal of ExplorationGeophysics, v. 12, p. 38–55.

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