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Gulf of Mexico “Bright Spots” –Early Shell Discoveries*

By Mike Forrest1

*Presented at AAPG Convention, March, 2002

Outline• 1967 - 1969 Shell “Bright Spot” history. • Shell Prospect Posy - 1970

EI 330 Field • Shell Prospect Pine – 1972

SMI 130 Field • Lessons.

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This paper describes oil exploration studies that were performed in Shell Oil Company (USA) during 1967 to 1972. Strong seismic reflections were observed over crests of structures in the Gulf of Mexico. After a calibration study was completed where petrophysical data was available, an operations/research team was formed and “Bright Spot” technology was applied in acquiring leases in the 1970 and 1972 federal offshore lease sales. Shell early discoveries include Eugene Island 331 that has 150 million barrels of oil and gas equivalent (MMBOE) and South Marsh Island 130 Field with 250 MMBOE.

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Index map of offshore Louisiana, showing location of Main Pass (MP) blocks 122/133 area, Bay Marchand Field (BM), Eugene Island (EI) Block 330 Field, and South Marsh Island (SMI) Block 130 Field.

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Acknowledgement

• Thanks to Shell Offshore (New Orleans) for permission to give this paper and especially for the data presented in this paper -“Data of the time”, 1967 to 1972.

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Thanks to Shell Offshore in New Orleans for permission to make this presentation and allowing the author to review old files so data “from the time” could be included in this paper.

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1967: Main Pass 122 - 133 Area

1.5 sec (5000’)

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During 1967, Mike Forrest, Shell geophysicist, observed high amplitude reflections that appear to conform to the shallow crest of a low-relief closure in the Main Pass 122/133 area, offshore Louisiana.

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1.5 sec, 5000’

1967: Main Pass 122 – 133 Area 5

During 1967, Mike Forrest, Shell geophysicist, observed high amplitude reflections that appear to conform to the shallow crest of a low-relief closure in the Main Pass 122/133 area, offshore Louisiana.

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1968, Main Pass 122 -133 AreaSonic LogElectric Log

24 NFG

23 NFG

16 NFG5000’/sec5000’/sec.5000’/sec vs. 6700’/sec

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Late 1968: S. Flank Bay Marchand FieldN S

3.0 sec, 12000’

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Late 1968. North-south seismic line across south flank of Bay Marchand field, where Shell, at that time, was preparing to bid ata lease sale on offshore block South Timbalier 26. The strong seismic event at 3.0 seconds on the north end of the line hasseveral hundred milliseconds of relief (about 2500 feet), and structural mapping indicated the strong reflection conformed to fault closure. Urban Allen, Shell geologist, made a “fault plane analysis” that indicated the amplitude anomaly (that was assumed to be associated with a sand) was juxtaposed with an oil sand across a small fault. After leasing the block, drilling found the amplitude anomaly corresponded with a 100 to 200 foot oil sand with approximately 100 MMBO.

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1968/1969 -- Example of amplitude anomalies Plio-Pleistocene trend, Offshore Louisiana

3.0 sec, 12000’

1.5 sec, 5000’

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1969

• “Bright Spot” term coined.

• Review several shallow Mio and Plio gas/oil fields – tied “bright spots” to pay with petrophysical “soft notch”.

• Operations/Research team formed.

• “Peak and Valley” days.

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1969. The term “Bright Spot” is coined in Shell New Orleans office. Gene McMahan. Shell geophysicist, looked over Mike Forrest’s shoulder one day and stated, “Those strong reflections look like bright spots.” The term became a fixture after discussions in coffee shop and meetings. During the spring of 1969, Mike Forrest reviewed several gas and oil fields in the Pliocene/Miocene trend in the shallow waters of the Louisiana shelf. A data package was prepared that showed gas/oil pays related to “Bright Spots” on seismic data and calibrated to low impedance (velocity multiplied by density) intervals on well logs. These field studies were shown to R.E. “Mac” McAdams, VP Exploration, and he immediately formed an operations research team to study and calibrate seismic “Bright Spots.” The next year, where there were several drilling successes and failures based on “Bright Spots” observed on then current Shell leases; was referred to as “Peak and Valley Days”.

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Prospect Posy EI 330 Field

Shell Block EI 331

1970 - 1971

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Prospect Posy introduction, EI 330 Field, 1969 and 1970. Posy was one of the first prospects where Shell made detail amplitude and thickness measurements. Shell leased block EI 331 and discovered 150 MMBOE. The overall EI 330 Field is 750 MMBOE.

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Prospect Posy (EI 330 Field) – “J” sand map

Shell 331 Pennzoil 330

••

•••

# 1# 3# 3

•# 1

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seismic l

ines

Prospect Posy structure map at “J” sand level with a good “Bright Spot” at approximately 1.7 seconds and conforming to structural closure (interpretation by Mike Forrest). The primary crest of the structure is located in the middle of block 330 but a secondary crest is present in the north half of block 331; both crests are part of large closure that spans several offshore blocks. Note the location of northeast-southwest seismic lines and also the locations of Shell 331 #3, Shell 331 #1, and Pennzoil 330 #1 wells.

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Prospect Posy, Line 388- 8486 migratedNESW

“J” Sd.2.0 sec. 7000’

│ Block 330Block 331

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Northeast-southwest seismic line across the main structure that is located in block 330.

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Prospect Posy, Line 375- 1127 stackSW NE

“J” sd

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Another northeast seismic line in the same vicinity as line in previous image. Note the “J” sand “Bright Spot”. This seismic line is the same as shown in image 8, which is shown as example of prospects with amplitude anomalies in the offshore Pleistocene area.

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Prospect Posy – “J” sand bright spot outline14

“J” sand “Bright Spot” outline which conforms to structural closure. The outline is based on unmigrated seismic data; the Fresnel Zone correction is shown on the map.

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Prospect Posy – Amplitude / Background

A/B 5

A/B 1.5From Aubrey Bassett Pazo

ProgramFrom Aubrey Bassett Pazo Program

From Aubrey Bassett’s Payzo Program

“J” Sd.

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Amplitude/Background (A/B) measurements at “J” sand level on a seismic line over crest of Posy. Measurements were made using program called Payzo, written by Aubrey Bassett, Shell Geophysicist.

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Prospect Posy – A/B map at “J” sand level

Amplitude/Background using Aubrey Bassett’s Payzo Program

A/B 4.0

A/B 1 - 2

331

A/B 3 - 4

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Amplitude/Background map at “J” sand level. The updip A/B is about four; note the consistent strong amplitude in the area around the location of Shell #3 well.

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W. Posy, “flat spot” (#3 location) E.

“J” sand

“L” sand

Line 388-6411

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Portion of east-west seismic line across the location of Shell # 3 well. Note the good “Bright Spot” at “J” sand level with a “Flat Spot” indicating a thick pay.

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“J” gross pay sand thickness mapChuck Roripaugh, 1970.Using Payzo program.

Prospect Posy

150’

0

100’100’

< 60’

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“J” sand gross thickness map, from seismic data, by Chuck Roripaugh, Shell geophysicist. The 150 feet gross thickness in northwest portion of block 331 in area of Shell #3 well thins to less than 60 feet on crest of structure in block 330. Leighton Steward, geology project leader, calculated the potential reserves for the “J” sand plus the deeper “L” sand, and Shell bid and won Block 331 for $13 million in the 1970 lease sale.

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66 NFG160’ gross

sand

66 NFG160’ gross sand

Shell EI 331 # 3, “J” Sand19

Portion of well log from Shell # 3 well that shows 160-feet of gross sand with 66 net feet gas. There is a good match between seismic interpretation and well data.

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EI 330 FieldShell #3 Shell

#1# 2 Penn #1

“J”

“L”

66 NFG 23’

42 NFO

25’ gas

25’

24’

17’ oil

7’ gas

W E 20

Geologic cross-section from Shell #3 to Pennzoil #1 well. Note the multiple oil and gas pays and the thinning of the gross interval and individual sands from Block 331 to crest of structure in block 330. All of oil and gas pays correlate with amplitude anomalies of varying quality.

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Posy – Shell #1 Log vs. Seismic

Well Log –Acoustic Impedance

Seismic-Runsum

“J” Sd.

“K”“L”

27 NFG31 NFO17 NFO

oil pay

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Shell Block 331 #1 seismic acoustic impedance from well data, with pays annotated, compared to the seismic data across the well. Seismic is displayed in Runsum format, developed after the 1970 sale; it is a pseudo acoustic impedance log derived by integrating the seismic trace (running sum = Runsum).

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Plio – Pleistocene “Trend Curves”

Refl. Coeff ( shale / gas, oil, water) vs. depth

1000’ 5000’ 9000’

0

.15

.25

.05

From Bill Scaife and Harlan Ritch - 1971

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Plio-Pleistocene “trend curves,” in this case defined as reflection coefficient vs depth, for gas, oil and wet sands. These curves, derived from petrophysical data acquired in the Pleistocene trend during 1970/1971, were used to help interpret amplitude anomalies in the 1972 Federal lease sale. Petrophysical trend curves are more complex than shown, as sand quality plays a major role in petrophysical measurements and interpretation.

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Prospect Posy Summary• First A/B and thickness mapping (Shell)

-“J” sand – thick gas.

“L” sand – first oil “bright spot” (hindsight)

• Several other qualitative BS’s were pay.

• EI 330 Field - 750 MMBOE Shell Block 331- 150 MMBOE

• Ref: EI 330 Field, Scotty Holland et al. AAPG website: Search and Discovery.

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Summary of Prospect Posy.

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SMI 130 Field

Shell Prospect Pine 1972 - 1973

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Prospect Pine introduction, 1972. First detail application of Runsum seismic processing (described in image 21) and calibration to petrophysical trend curves. “Bright Spots” were used to successfully predict oil pays; this was very important at the time as oil was a much more valuable resource than gas.

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West Pine Prospect Pine, SMI 130

130

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Pine

ESEWNW

West Pine Prospect Pine

1.5 sec, 5000’

Shell #1 SMI 130

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Prospect Pine and West Pine ESE-WNW seismic line. Stacked “Bright Spots” are present on west flank of salt/shale diapiron Prospect Pine, and a single “Bright Spot” is present across the syncline to the west at Prospect West Pine. The Pine amplitudes are oil and gas pays, whereas the West Pine amplitude, which has the same measured amplitude as an oil pay across the syncline at Pine, is caused by low-saturation gas in a sand. Shell tested low quantities of gas, and the sonic log showed cycle skipping suggesting the sand had about 10% gas saturation. The theory of a low-saturation gas sand having a seismic amplitude as a high-saturation gas sand was developed at about the same time as the West Pine observation.

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Prospect Pine – RUNSUM (Integration)W E

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Runsum of Prospect Pine seismic amplitude package.

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182’ NFO230’ NFO21’ NFG

Prospect PineW E 28

Geologic cross section, with oil and gas pays, shows the first two exploration wells on Pine, a downdip and an updiptest.

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Prospect Pine #1 and 2 wellsSynthetic Seismogram - Runsum

seconds

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Synthetic seismogram and oil/gas pay thicknesses from petrophysical data of two exploration wells at Prospect Pine.

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Prospect Pine/West Pine Summary

• First application of “RUNSUM” processing and petrophysical “TREND CURVES”.

• Original estimate of 100 MMBO, based on high probability “oil calls”. Current est over 250 MMBOE.

• West Pine - first recognition of low saturation gas problem (LSG).

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Prospect Pine summary.

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Shell Discoveries Using “Bright Spots”

• GOM Shelf – 1.5 to 2 BBOE

• GOM Deep Water – Approx. 4 BBOE

Presence of “bright spots” was a key factor in entering deep water during 1983 to 1986.

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Shell discoveries using “Bright Spot” technology, 1970 to 1998.

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• Good ideas come from operations people -follow-up with research TEAM.

• New ideas - requires persistence“BEWARE OF THE SKEPTICS”.

• In hindsight, good ideas are very often simple and easy to understand.

• If technical staff and management agree on application of new technology,“GO FOR IT”

Lessons32

Lessons from Shell initial “Bright Spot” studies and Prospect Posy and Pine successes.

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Shell Team - 1969 to 1972

• Billy Flowers, Glenn Robertson, Mike Forrest, Urban Allen, Dick Grolla, Aubrey Bassett, Chuck Roripaugh, Ray Thomasson, Leighton Steward, “Mac” McAdams, Miner Long, Manny Baskir, Dave DiMartini, Gene McMahan, Lee Backsen, Bill Scaife, Harlan Ritch, Sam Mitchell, J.T. Smith, Jules Laine, et al.

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List of the Shell team members (successful exploration is always a team effort) who played a significant role in “Bright Spot” technology studies, 1967 to 1972.