15	GEOPHYSICAL EXPLORATION IN TRINIDAD AND TOBAGO, 1900-1990 PART 1:1900-1960 Ellison Welch, Ministry of Energy

INTRODUCTION

The early oil wells in Trinidad were sited first on the basis of oil seepages and later, on the basis of geologic mapping. Geophysics was first employed in the 1930's. The earliest reference to the successful use of a geophysical tool (jointly with geology) in the search for hydrocarbons is as a result of the discovery of the Barrackpore/ Penal field in 1941 (Ablewhite & Higgins, 1965 ). Quoting G. E. Higgins, 1956 with respect to this noteworthy event:
"The first recorded geophysical survey in Trinidad was carried out in 1932 when a refraction survey was made near Brighton. TLL, however, first introduced reflection seismic survey methods over their holdings in Trinidad in 1937. The seismic party operated in the Penal - Barrackpore area.

Higgins summarizes his report as follows:
"The drilling of Barrackpore 336 in the Clarke Road area was the culmination of persistent seismic work made during 1937-1940 and 1946-1947 although the discovery must be attributed directly to the seismic method, for the survey revealed the anomaly which otherwise would not have been detected. . .

Undoubtedly the most successful usage of geophysical methods has been offshore where the geology is not easily accessible; the first seismic success offshore Trinidad & Tobago being the discovery of the Soldado field in the Gulf of Paria in 1955.

Because of the difficulty of obtaining in public files, detailed historical data about these early years of oil exploration, it is thought best to report the history of geophysical exploration in chronological form, employing side notes to clarify matters where necessary. This historical review is done in two parts. Part 1 covers the period 1900-1960, Part 2 reviews 1961 - 1990.Theformerperiod deals with the pre digital computer days and the transition to digital modern day recording and processing. The latter is substantially a record of how the full digital computerization of the geophysical industry and the implementation of many theoretical discoveries affected geophysical exploration in Trinidad & Tobago.
Early information is obtained from the Administration Report of The Inspector of Mines and Petroleum Technologist (IMPT)of the Mines Department. This was the forerunner of the Ministry of Petroleum and Mines (established in 1962) and later, the Ministry of Energy.

There is inadequate information on local geological/geophysical activity for the period, late 1950's to the mid 1960's (apparently because of teething problems in the formation of the Ministry of Petroleum and Mines and also lack of detailed reports). For this period
the only recourse was to rely on the publications of the AAPG, but even here the information is very scanty (The source of the information for the AAPG was the Mines department).


1900/33
The first references to geophysical surveys being conducted in Trinidad relate to gravity and magnetic surveys in the reports of IMPT for the year 1931;
"Exploration licence to United British Oilfields of Trinidad, Ltd. over 1715 acres Crown Lands for the purposes of carrying out a geophysical survey Reg. No.4046 of 1931, supplemental to No.2178 of 1931."

and for the year 1933;

"The torsion balance and magnetometer surveys from Cedros to Moruga mentioned in my last Year's report did not add materially to our present knowledge though they gave confirmatory evidenced of what was already known."

The torsion balance referenced to above was a gravity tool used to measure gravity gradient and curvature rather than gravitational acceleration. This tool was used extensively for 2 decades but was eventually replaced by the Gravimeter in the mid 1940's.
In 1936 the gravimetric method was still the main geophysical tool employed as evidenced by the IMPT in his report for 1936:

"In addition to a general increase in drilling operations, widespread exploration surveys have been carried out during the past year, and this important work is still in progress. These exploration surveys have included the examination of extensive areas by geophysical methods (mainly gravimetric).'

But for the year 1937 the first mention of the use of the seismic method is made:
'Exploration survey work has continued to be very actively pursued in the Colony during the past year and in this connection ft is of interest to record the extensive use made of the seismic method of geophysical surveying. During the past year this method has, to a very large extent, superseded the gravimetric method which had previously been mainly used.'
1939/48
Geophysical work was interrupted during World War 2, recommencing in 1946, the report for 1946 states:
"Considerable geological work, including that of two seismic parties, was undertaken during the year."

Even though the scale of operations in the oil industry in 1947 was limited by material and monetary shortage, much geological and geophysical work was done. For 1947 it is reported that:
A considerable amount of geological work was done in order to demarcate areas for deeper exploratory drilling. Seismic work was carried out by three field parties, two of whom completed their programmes during the year. Preliminary gravity surveys were commenced on a large scale, the areas examined including parts of the Gulf Of Paria."

The IMPT report of 1948 contains the most extensive reporting on geophysical surveying to-date. This was in apparent recognition of the fact that:
"More attention was given to exploration than formerly since diminishing crude reserves is a cause of concern to more than one Company."
The work done in this year included:
1. "Trinidad Northern Areas employed Gravimetric Exploration Company to survey the entire Trinidad land area south of the Northern Range and parts of the Gulf Of Paria beginning in 1946."
2. Trinidad Petroleum Development Co. Ltd employed Gravimetric Exploration in 1947 to survey 241 square miles using 1225 stations in the Erin basin eastward to Tableland and Moruga and also to survey27O square miles offshore the south coast in 1948 utilizing a further 476 stations."
3. "Reflection seismograph surveys were carried out by Seismic Services Ltd (UK) north of the Forest Reserve Field and at Barrackpore for Trinidad Leasehold Ltd, also in the Erin Basin, North Ortoire and Penal Areas for United British Oilfields of Trinidad Ltd. Apex Trinidad) Oilfields Ltd, and Kern Trinidad Oilfield Limited both employed Seismic Services Ltd for reflection surveys over the synclinical portion of the Apex Field and over the south flank of the Central Range respectively."
4. "The Oscar Weiss Geophysical Survey Company had both seismic and gravitimeter parties in the field. This company conducted a gravitimeter survey in the Lizard Spring and Guayaguayare areas for Trinidad Leaseholds Limited and over the Pitch Lake Area on behalf of Antilles Petroleum Co. A reflection and r fraction survey was also made for the latter company over the Oropouche area. The National Mining Corporation also employed the Oscar Weiss Company for surveys in the Palo Seco-Erin area, also in the areas of Otaheite and South Penal"
1949 / 60
The surveys which began in 1948 were completed in 1949. The following year 1950 was devoid of field activities. Activity recommenced in 1951 when:
"UBOT Ltd conducted a geological survey in the Ortoire basin and started a seismograph survey. Seismograph Service Limited also shot a line of about four and one half miles for Apex Trinidad Oil fields Limited across their Fyzabad and Coora leases."

Dominion Oil Limited of Canada, a company which in later years pursued a very aggressive exploration policy, especially on-shore, began geological and geophysical surveys in 1952.

The IMPT report for this year records:
"Marine seismograph surveys were conducted over the greater part of the Gulf Of Paria by both Trinidad Northern Areas Limited and by Dominion Oil Limited. Seismic surveys on land were made on the behalf of Trinidad Petroleum Development Co. Ltd and Apex Trinidad Oilfields the northern basin for TNA Ltd.'

The year 1953 was a very busy one in the industry for geophysical exploration. The following companies: TPD, UBOT, Apex and PCOL had interest in seven lines which were run in the Siparia district. TPD also ran three lines in the Moruga-Bouffe district and with Apex, four lines in the Palo Seco and Erin districts. UBOT completed a seismic survey in the Ortoire district and TNA conducted one survey in the Charuma area. TLL also obtained seismic data over their Singuineau, Kapur Ridge, Mayaro, Guayaguayare and Morne Diablo holdings. Meanwhile, DOMOIL was very active acquiring seismic data in the Gulf Of Paria, the Northern Basin and the East Coast.

By 1956 DOMOIL had established itself as the most aggressive exploration player on the scene. Domoil is reported by the IMPT as being involved in exploratory drilling, structure holes drilling, and conducting geophysical surveys:

"Over a large area in the northern-eastern part of the Gulf 0f Paria using magnetic tape equipment. This brings the length of Marine seismic line surveyed by Dominion Oil Limited up to 1,580 miles."

In 1956 IMPT records that:

"Several regional reflection tie lines were shot as well as two long refraction lines, while one seismic party was occupied on land for the entire year. The length of this company's (DOMOIL) seismic survey fines on land now amounts to 980 miles. Gravity readings have been taken at approximately 6,700 stations (5,645 on land and
1,048 marine)."

No information is located for 1957. From The Report Of The Commission Of Inquiry Into The Oil Industry, 1963/64, the following companies carried out geophysical work:
1958 Company Party Months
DOMOIL .5
SHELL 2.0
TRINMAR 1.5
BP .13
DOMOIL 2.0
TEXACO 8.5

1960 The only activity reported for 1960 was 1.25 party months of geophysical work by SHELL.

For the years 1957 to 1960 no detailed information on surveys was located.

REFERENCES
1. Ablewhite & Higgins, Caribbean Geological Conference, 4th, March 28-April12, 1965, Transactions p.41

2. Trinidad and Tobago Inspector of Mines and Petroleum Technologist. Reports. 1900-1960

3. Trinidad & Tobago Ministry of Petroleum & Mines. Annual Reports. 1968 - 78

4. Trinidad & Tobago Ministry of Energy Annual Reports. 1978 - 90

5. American Association of Petroleum Geologist. Bulletin 1958-1967

6. Higgins. Society of Exploration Geophysicist. Geophysical Case Histories. Volume 11. 1956. P.261.

7. Report Of The Commission of Enquiry Into The Oil Industry, 1963-64.

EDITOR'S NOTE: This article is part I of a two part series. The section 1961-1991 will appear in the next edition of the newsletter

Home | About Us | Links To The World  |  Publications | Upcoming Events |

Feedback | Executive Members | Geology |Teaching Resources| Virtual Field Trip

THE GEOLOGICAL SOCIETY OF TRINIDAD & TOBAGO
P.O. Box 3524, La Romain, Republic of Trinidad and Tobago, W.I.

Comments or Questions?