FIELD DEVELOPMENT USING SEISMIC DATA AT LITTLE MITCHELL CREEK FIELD SHUIQUAN LI

JOHN LONG (speaker) MIKE LANE

START

LMC 3D seismic summary as of January 5, 2012 Modeling of the Minnelusa reservoir log data to simulate surface seismic response indicated that 3D seismic data should be able to determine reservoir sand extent seen at Little Mitchell Creek field. The Geokinetics 3D dynamite seismic survey was acquired and was processed by Excel, providing good data quality. Synthetic seismograms created by applying a minimum phase Ricker wavelet to sonic logs from several wells were used to correlate the well data to the seismic data. The correlation is good. In the center of the Little Mitchell Creek field the amplitude of the Minnelusa event is very high where over 50’ of B Sand is present. Judging from visual inspection the Minnelusa event has a dominant frequency of 35 hertz which is typical of seismic data from this depth. At 35 hertz seismic data has a ¼ wavelength constructive interference peak when the B sand thickness is 80’and still shows high amplitude when at 50’ thickness. This explains the strong seismic amplitude seen in areas where the B sand thickness is 50’ or greater. A location ENE of the #15-10 well and NEN of the #15-1 well is proposed where a high amplitude, structurally high 30 acre area updip of the #15-10 well and on strike to the #15-9 and #15-2 wells is seen on seismic data. It is estimated that this location will encounter 50’ of B sand and will be 10’ high to the #15-10 well. The acreage southeast of the #15-2 well may be prospective, but the 3D seismic data as currently processed is not capable of determining the B sand thickness in this area. As mentioned above, the Minnelusa event has high amplitude when the B sand is greater than 50’ thick, so low amplitude in this area suggests that the B sand is less than 50’ thick. Synthetic seismogram modeling shows that as the B sand thickness decreases to 30’ destructive interference reduces the amplitude to less than half of the peak value at 80’. Once the B sand thickness is below 30’ the amplitude continues to decrease as the destructive interference increases. This fact is verified by comparison of two wells that have identical seismic response, yet well #43-14(aka #15-2) has 30’ of B sand and well #41-23 has no B sand. Other factors also affect amplitude in this area. The #13‐13 well is in a very low amplitude area, yet encountered 42’ of depleted B sand. Synthetic seismogram modeling of the #13‐13 well shows that the presence of 14’ of A dolomite in this well, which is relatively thick, contributes to loss of amplitude due to additional destructive interference, revealing another factor besides B sand thickness that affects seismic amplitude. Thus variations in ¼ wavelength peaks at various B sand thicknesses, A dolomite thickness, and numerous other seismic responses created by variations in shale, dolomite, and sand thicknesses affect seismic amplitude and make it difficult for seismic data to determine B sand thickness in this low amplitude area where B sand thickness is generally less than 30’. The presence of erosional channels seen on seismic data in the acreage southeast of the #15-2 well further complicates selecting favorable locations in this area. Seismic cross sections in the Little Mitchell Creek 3D occasionally show 400’ wide, at least 25’ thick Opeche filled erosional channels cut into the Minnelusa surface. A map view of these features reveal several channels with low amplitude. Channels such as these are called wadis in desert environments. One of these erosional channels surrounds the entire eastern side of Little Mitchell Creek field and is the abrupt updip termination of the Little Mitchell Creek oil reservoir. This channel and two other channels meander across the acreage southeast of the #15-2 well. The B sand has been thinned or removed where these three erosional channels occur, creating barriers and restrictions between the remnants of B sand in this area, but still possibly allowing depletion. Thus drill a field extension well southeast of the field is considered very risky.

Little Mitchell Creek Field

lower B sand

upper B sand

Initial subsurface work by Gene George

90 ms

66 ms

30% φ

11% φ

barrier

2,674,258 BO

φ=(ms-55.5)/(154.55.5)

6% φ

61 ms

barrier?

lower B sand

upper B sand

05-06393 Gene’s reservoir barrier

o/w contact in lower sand

o/w contact in upper sand

-3125

-3152

Upper and lower B sand

o/w lower than WIW#1 well ,

productive

o/w higher than 14-11, but not productive

Higher than 14-11, but

not produced o/w contact in upper sand

-3125

o/w contact in lower sand

unknown downdip area, below oil water contacts, where upper and lower B

sands are in communication

-3152

possible explanation for different o/w contacts

Future Loc?

Why not productive?

Future Loc?

Reservoir volume?

Questions for seismic?

o/w 27’ lower than WIW#1 well o/w

Minnekahta

Upper B sand

005-28882

005-05863 74’ of Opeche

50’ of lower B sand Pf 7470-7510 (38’)

487,306 BO 2,454 MCF

1,112,866 BW

Seis shows 22-24 is 13 ms low to Hembdt, but it is 42’ high at B

dolo level 2D Seismic

data

-3108

Minn B dolo-3108

Minn B dolo-3132

90’ of Opeche

-3066

Upper B sand NP

C sand

Thk B sand Thk Opeche Thk Opeche

Seis shows no change between these two areas

Seis shows major change between these two areas

Loss of positive amp Fair positive amp

top Minnk-2968

top Minnk -2992

Seismic problems: time/depth problems and response inconsistencies

Fair positive amp

10’ of B sand

65’ of B sand

no B sand

#15-3

event present if B sand >10’

Seismic modeling suggests high amplitude where sand thick, resolvable down to nearly 20’

14-18

1

1

1

22-11

21-11 11-1 1-12

1-24 21-1

1

1

22-10

1 mile N

7.25 SM LMC 3D

Unit outline

Area to be imaged with

full fold

Area to be permitted for surface use by Geokinetics

area to be imaged

LMC 3D survey parameters

GEOKINETICS

Well survey

1 mile LMC 3D survey layout

Shot by Crew 306 in August, 2011

5

8

3

1

1

2

9 11

10

14

11

Surveyors location

GoogleEarth location

1000’

origianl map location

well locations tied to seismic

Figure 10b, synthetic seismogram and well-tie

LMC points

Synthetic tie confirmed nearby velocity survey

(six miles south)

Minnelusa reservoir event amplitude 1000’ N

Figure 8, dominant frequency of Minnelusa seismic data is 25 to 55 htz

Synthetic Seismogram; 80’ – 30’ of sand at 35 hz

7000

7100

7200

7300

7400

30’ of sand 50’ of sand 80’ of sand

Amp = 1

Amp = 3/4 Amp = 1/2

Synthetic seismogram determination of peak amplitude thickness for 35 hz data

highest amplitude at 80’ of sand

Very low amplitude when sand < 30’

#15-10

#15-7

Minnelusa channel feature 1000’ N

Proposed location

Proposed Location 2 ms (10’) high to #15-10

estimate 50’ of B sand

-3049 80’ of B sand high wtr cut

B sand

8’ of wet B sand

erosional channel

high amplitude low amplitude

Proposed Location

400’

#41-14(15-7) #15-10

775’

No las sonic

Proposed Location

photos of modern wadi

Single channel, approximately 500’ wide, similar to eastern limit of Little Mitchell Creek

field

Photos from area near Nahal Paran, Negev desert, Israel

80

30

50

60

50

50

60

20

55

40

40

0 0

0

10 #15-10: high wtr cut

#15-10

#15-3

#15-1

20

#15-2 #13-13

40

low amplitude

high

amplitude

erosional channels

#15-8

#15-9

(15-7)

#41-23

0

40 acres

Proposed location in southeast area

Minnelusa channel complex 1000’ N

Possible Location

#13-13; 42’ of B sand low amplitude

#15-9 & #15-2: high oil cut

erosional channel

Minnelusa channel

erosional channel

80’ 60’ 0’ 42’ 30’

30’

0’

Similar seismic response 30’ of sand- no sand

channel channel

Comparison of Minnelusa

seismic event response

high amplitude response sand over 50’ thick

low amplitude response sand 42’ thick

medium amplitude response sand 30’ thick

photos of modern wadi

Area cut by several channels, similar to acreage southeast of #15-2

Photos from area near Nahal Paran, Negev desert, Israel

0’

Amplitude data cannot distinguish 30’

of sand from no sand in some areas

similar seismic response 30’ of sand - no sand

30’

#15-2(506414)

Cum: 1 MMBO

41-23

#41-23 D&A

(520010)

“rubble”

Minnelusa A Dolomite masks

B sand reflector in #13-13 well

7439

7425

14’ of A dolomite

25’ of B

dolomite

42’ of B sand 42’ of 8-17% porosity B sand

C sand

#13-13 well tested oil but was depleted so it is not isolated by channel. It would not produce.

FIELD DEVELOPMENT USING SEISMIC DATA AT LITTLE MITCHELL CREEK FIELD

ATTRIBUTES

LMC 3D seismic summary: April 30, 2013 update Shuiquan Li of EORI has conducted further analysis of the LMC 3D data selecting “Envelope”, “Relative Impedance”, and polarity attributes. Envelope registers reflection strength and relative impedance measures changes in acoustic response. The values of these two attributes where noted at wells of interest. It appears that the Envelope attribute has high reflection strength where the B sand is thickest and a weak response where the B sand is thin, similar to the amplitude response. The Relative Amplitude attribute shows strong response in thick porous sand zones and weak response in low porosity zones such as dolomite and what are called “rubble” zones. Polarity was used to confirm the correct seismic event for the top of the Minnelusa and top of the B dolomite. Variations of these attributes between wells and extrapolated beyond well control were used to predict changes in lithology. The resulting map of the Envelope attribute is very similar to the amplitude map, showing a strong response where the best oil wells are located. A moderate Envelope response marks a distinct area where poor B sand porosity inhibits continuity between the center of the field and the #14-11 well on the isolated northwest edge of the field. A moderate Envelope response occurs in the southeast field area that has been dissected by several channels yet has still yielded very good oil production. The attributes could not distinguish the presence of sand when the thickness is below 30’ in the southeast area. The Envelope attribute was able to detect the presence of what is called the “rubble zone” and what appears to be unusually thick B dolomite. Rubble zones are erosional debris deposited in topographic lows on the eroded Minnelusa surface. The rubble zones appear as linear features very similar and adjacent to the channels seen on the amplitude data. The interpreted thick B dolomite area appears to be a linear feature adjacent to the previously discussed channel that is the eastern limit of Little Mitchell Creek field. The thick B dolomite feature is centered 400’ east of the #15-7, while the channel is centered 400’ west of the #15-7 well. It is possible that differential compaction over the thick B dolomite feature created topographic relief on the exposed surface of the Minnelusa during early Opeche time that influenced the path of the trapping erosional channel. The two main goals accomplished using the seismic data were selecting an optimum field extension location on the northeast side of the field and confirming that a location on the southeast side of the field has high risk due to possibility of depletion or isolation. Unexpected findings from seismic data include establishing that a channel creates the critical northeast closure for the field, showing that several channels may isolate or inhibit reservoir continuity in the southeast part of the field, and that seismic data can predict rubble zones and thick B dolomite. The seismic data was not able to determine the thickness of reservoir sands when less than 30’ thick, and therefore did not aid in establishing more exact reservoir geometry to aid with oil volumetric calculations. Furthermore the area of communication between the upper B sand and the lower B sand could not be seen on seismic data since the barrier between these two zones is below seismic resolution.

Figure 14a, mathematical definition of “envelope” attribute

Envelope is named as a reflection strength which detects subtle lithological changes, major lithological changes that are caused by strong energy reflections and sequence boundaries [11]. Under the current display sittings for ENV sections a bright blue ENV means large reflection strength while a red ENV does weak reflection strength. The larger the acoustic impedance contrast across an interface the reflection strength from the interface is stronger and the larger ENV is. After removed the phase component from the amplitude data, ENV could have a better detectability than amplitude itself.

Figure 14b, definition of relative impedance attribute

Relative acoustic impedance (RAI) is apparent acoustic contrast, which indicates sequence boundaries, unconformity surfaces and discontinuities. After calibrated by well logs, RAI could approximately constraint the Minnelusa formation, from Minnelusa top down to the B dolomite. In addition, under the current display settings for RAI sections in this seismic interpretation RAI color is bright yellow (large value) for a porous zone, and change to darker red (small value) in a tight rubble zone.

“envelope”

Figure 16a, “envelope” attribute at top Minnelusa

strong reflection strength

weak reflection strength

Figure 15h, seismic attributes in thick sand area

polarity amplitude

envelope relative impedance

Figure 16k, Cumulative oil produced to date. Best production is in high amplitude area

Table 1, LMC production

Figure 16l, averaged annual oil production rate. Radius corresponds to annual rate of oil production.

envelope envelope

Figure 4a, “Envelope” attribute response for wells with good reservoir sand

very thick sand strong seismic response

thick sand weak seismic response

channel complex Minnelusa A dolomite present

0’

Amplitude data cannot distinguish 30’

of sand from no sand in some areas

similar seismic response 30’ of sand - no sand

30’

#15-2(506414)

Cum: 1 MMBO

41-23

#41-23 D&A

(520010)

“rubble”

“Envelope” attribute cannot distinguish

30’ of sand from no sand in some areas

polarity amplitude

envelope relative impedance

Figure 15q, seismic attributes for well in “rubble” area

polarity amplitude

envelope relative impedance

envelope

Figure 16j, white stripes are rubble zones(or tight zones) identified from seismic attributes. The background is areal “ENVELOPE” attribute on the Minnelusa top

strong reflection strength

weak reflection strength

Channel as seen on amplitude data

erosional channel on west side of 15-7

“HR” amplitude “high resolution” filter applied

B dolomite thickness

B dolomite thickness anomaly seen on “envelope” attribute data

“envelope”

thick B dolomite on east side of 15-7,

“HR” amplitude “high resolution” filter applied

amplitude

mig“HR” (harmonic freq boost)

migrated Mig Rho flt (high freq boost)

final stack

Processer: Tom Szot Excel Geophysical Services Denver High-resolution stack is an attempt to pull more frequency out of the data by going into the harmonics and boosting them. For example, if you have a vib line that swept to 120 hz, there may be useful information in the harmonics up to 240 hz. We define how high we wish to push the frequency (usually only an extra 30 hz or so) and boost the amplitude of those frequencies. Not every interpreter thinks this is a good (or even a valid) idea, but several have commented favorably on the results and have found them useful. We think that it should be used as an extra tool to refine a potential target. Looking at the slides you sent, the difference in amplitude near well 521998 may be telling you something important that the standard sections don't show. Certainly worth thinking about. Lots of processing centers are experimenting with this concept. Ours was written internally about three years ago and I have used it on a number of projects. Our programmer defines it this way: "The 3D High Frequency Enhancement tool performs high frequency enhancement of seismic data in 3D. The reflectivity series is extracted from the migrated dataset using a constrained genetic algorithm. The reflectivity series is interpreted to find the min and max frequencies we can pull from the dataset. A time and space variant wavelet is pulled from the original dataset. The wavelet bandwidth is expanded to include the new min/max frequency range using a complex filter design that weights the original frequency range higher than the expanded frequency range. The new wavelet is convolved with the reflectivity series to produce the hi-res output."

thick B dolomite on east side of 15-7,

channel and B dolomite thickness anomalies seen on standard seismic data

erosional channel on west side of 15-7

Future Loc?

Why not productive?

Future Loc?

Reservoir volume?

o/w 27’ lower than WIW#1 well o/w

Why not productive? Depleted

not answered by seismic

Future Loc? Yes, to be drilled

Future Loc? probably depleted or isolated by channels

envelope

Reservoir volume? not answered by seismic

o/w 27’ lower than WIW#1 well o/w up. and low. B sands connected at depth

Not resolvable on seismic

area of weak B sand response due to Minnelusa A dolomite, rubble zone and channels

strong reflection strength

weak reflection strength

FIELD DEVELOPMENT USING SEISMIC DATA AT LITTLE MITCHELL CREEK FIELD

END