EXPLORATION COMPLEX GEOLOGY YIELDS SURPRISE OFF TRINIDAD

G. Alan Petzet
Exploration Editor

Incredibly complex geology is still hiding significant hydrocarbon accumulations in Trinidad and Tobago, where the first commercial well was drilled in 1908.

Amoco Trinidad Oil Co. tapped into one of those surprises last year in Teak field. It drilled an offshore well, Teak E 3, that has produced at the rate of 7,000 b/d of oil.

The company pointed out that the Teak E-3 well illustrates how new technology can unlock the secrets of complex geology and "how fiscal incentives from enlightened government policy can rejuvenate operations and encourage investments."

Geology of the area is typified by highly faulted, anticlinal Pliocene structures that contain numerous, generally small sandstone reservoirs due to the complex faulting.

Amoco's Teak field has 14 oil producing horizons and 40 reservoirs. The company's Samaan, Poui, and Mora oil fields and Cassia gas-condensate fields share the same characteristics.

Geology and reservoir characteristics make for decline rates of 30-35%/year.

"HOOK" WELL

Engineers call Teak E-3 a "hook" well, an extreme example of deviated drilling. The well was drilled about 9,000 ft to reach a true vertical depth of 7,800 ft.

The well was curved back nearly 180 from its initial course to penetrate the target virgin fault block and avoid colliding with existing wells. Hole angle averaged about 30 and reached more than 50.

Use of a downhole steerable motor permitted Amoco to adjust drilling angle without rotating the drillstring at the surface. Measurement while drilling equipment fed back data on well angle and direction, rock type, and hydrocarbon indications.

The well has the highest flow rate Amoco Trinidad has gauged and is less than 1 mile from where the company made its initial discovery off the island nation in 1969, says an Amoco publication.

IMPROVED INCENTIVES

Amoco said sweetened government incentives played a big role in company decisions to make large investments in Trinidad and Tobago.

At yearend 1988, the government cut the tax rate retroactive to January of that year and made other changes to provide investment incentives.

Teak E-3 was part of a stepped up drilling campaign that employed five rigs by yearend 1989.

One of the rigs, Well Services Marine No. 1, was built at Amoco's request and owned and operated by a Trinidadian company. Its modular design reduces the time required to move between drillsites to 7 days from 30 days.

Since beginning operations in Trinidad and Tobago in 1961, Amoco has drilled 90 exploratory and 188 development wells, installed 16 platforms, and built extensive onshore oil storage, treatment, and handling facilities.

Cumulative major cash spending has amounted to more than $1.2 billion, and operating expenses total more than $4.4 billion.

The company has paid the government about $9.6 billion in taxes, royalties, and other fees.

WHAT'S AHEAD

The incentives appear to be slowing the country's production decline and luring more operators.

OGJ estimates Trinidad's production was 150,000 b/d in March 1990, compared with about 155,000 b/d in 1988 and about 175,000 b/d in 1985.

Amoco's gross production in the country was about 72,000 b/d last year, compared with 70,000 b/d in 1988 and 94,000 b/d in 1985.

Units of Exxon, Chevron, and Total CFP and the state companies Trintoc and Trintopec signed a 5 year program to explore onshore Trinidad's southern oil belt for deeper horizons thought to be analogous to nearby Venezuela's hot El Furrial trend (OGJ, Nov. 27, 1989, p. 33).

Mobil and Trintopec signed an accord that will result in seismic surveys and drilling of at least four wells on 180,300 acre offshore Block S-11 (OGJ, Oct. 2, 1989, p. 46).

A 14 page article in this magazine by Philip R. Woodside of the U.S. Geological Survey gave an extensive rundown of Trinidad and Tobago's petroleum geology and almost a page of references (OGJ, Sept. 28, 1981, p. 364).

Another article described the stratification of oils in the Columbus basin, where Amoco is active (OGJ, Sept. 26, 1988, p. 72).

Copyright 1990 Oil & Gas Journal. All Rights Reserved.