Onshore Exploration Drilling Success in Southern Basin, Trinidad*

Xavier Moonan1 and S. Harrypersad1

Search and Discovery Article #11293 (2020)**

Posted January 27, 2020

*Adapted from oral presentation given at 2019 AAPG Latin America & Caribbean Region Geosciences Technology Workshop, Recent Discoveries and Exploration and
Development Opportunities in the Guiana Basin, Paramaribo, Suriname, November 6-7, 2019
**Datapages © 2020. Serial rights given by author. For all other rights contact author directly. DOI:10.1306/11293Moonan2020
1
Touchstone Exploration, Fyzabad, Trinidad & Tobago (XMoonan@touchstoneexploration.com)

Abstract

From 1857 to present, some 13,000 oil wells have been drilled onshore Southern Basin of Trinidad producing more than 1.5 billion barrels of
oil to date, primarily from Late Miocene to Pleistocene deltaic sandstones. Just under 2000 of those wells drilled and tested Middle Miocene
deep-water turbidites, with less than a hundred testing Cretaceous reservoirs. With scores of old, abandoned and to some extent
stratigraphically mature fields scattered along its length and breadth, and the ever-increasing rate of decline of the country's oil production, the
basin required a new wave of exploration, to stratigraphically older and deeper reservoirs. In 2013, the Ministry of Energy launched an Onshore
Bid Round, the first in just 15 years Three blocks adjacent to established oilfields with production primarily from Middle Miocene Herrera
deep-water turbidite sandstones, were marketed and 11 bids were received. The Rio Claro Block was awarded to Lease Operators Limited; the
St. Mary's Block was awarded to Range Resources and the Ortoire Block was awarded to Touchstone Exploration. Each block entailed
minimum work obligations of 4 exploration wells each to targets of at least 5000ft. In 2019, the exploration drilling campaign kicked off for
both Lease Operators Limited and Touchstone Exploration. LOL drilled their Ah Yah Yie well to a TD of 6150ft encountering stratigraphy as
old as Early Miocene. Unfortunately, the well failed to encounter effective reservoirs and was plugged and abandoned. LOL's second well,
Barakat was drilled in vicinity of the Balata East field, where it encountered oil bearing Herrera sandstones in structures on trend with the
Balata East thrust sheet. This well has thus proven that the current oilfield can be extended with careful outstep drilling into tear fault bound
thrust sheets to the west and south west. Touchstone Exploration drilled their Coho well testing a SW plunging anticline immediate south of the
Penal Barrackpore anticlinal trend, in the Tableland area and successfully discovered gas and condensate in Herrera sands within two thrust
sheets. Touchstone's Cascadura well was then drilled testing a structure on trend with Penal Barrackpore anticline immediately south of the
town of Rio Claro. The well encountered three Herrera thrust sheets as prognosed with oil bearing sandstones at two structural levels. The
lowermost of these sandstones appear to be near vertical to overturned and correlates well with the Overturned Limb or Intermediate Herrera
from Penal Barrackpore. A string of successful drilling, supported by extensive structural modelling, has breathe new life back into Southern
Basin, de-risking adjacent prospects and opening more opportunities for exploration investment. Adamant optimism, sound geological concepts
and supportive policies are the fundamental principles to ensuring the rejuvenation of T&T's hundred-year-old industry.
Xavier Moonan & Stefon Harrypersad
Touchstone Exploration
 Acknowledgements
• The Ministry of Energy and Energy Industries, Trinidad and Tobago
• Heritage Petroleum Company Limited
• Lease Operators Limited
• Upstream Management Limited
• Touchstone Exploration Trinidad Limited

All rights to the presentation and information contained therein are reserved by Touchstone Exploration Trinidad Limited as Operator of the Ortoire
Block and Lease Operators Limited as Operator of the Rio Claro Block and are not to be republished in any medium without express written consent
from Touchstone Exploration Trinidad Limited and Lease Operators Limited and Joint Venture Partner Heritage Petroleum Company Limited.
Trinidad – ‘the graveyard of geologists’
• First oil well drilled by the American Merrimac
Company in 1857 at a depth of 280ft but was not
commercially viable.
• Some 13000 wells have been drilled, producing
just over 3.5BBO and 12TCF Gas, primarily from
Pleistocene to Late Miocene deltaic sandstones.

Bongos, Hi-Hat, Boom

Bele, Tuk

Le Clerc
Victoria
Concepcion
 The imaging challenge – Onshore Southern Basin Consortium 2D Seismic Line TD 91-177

N SE
W
• Acquired and processed by Halliburton Geophysical for Exxon Trinidad Ltd and SBC partners in 1991 • 9 geophones per string, 2 geophone strings per group, array equally spaced. Fold coverage – 60
• Symmetrical split spread. Total Line length 21km. • Processed using standard Promax processing with AGC and predictive decon to remove multiples,
• 20m hole depth, 15lb charge size. 240 channels, sample rate 2ms. 30m receiver station interval , noise and spiking
60m shotpoint station intervals • There is risk of sideswipe artefacts
 The imaging challenge – Onshore Southern Basin Consortium 2D Seismic Line TD 91-177

N SE
TOP CRUSE: L. Miocene/E.Pliocene LENGUA/KARAMAT (Gg7): M. Miocene HERRERA (Gr7bc ): M. Miocene RETRENCH (Gg 32): E-M. Miocene NAPARIMA HILL: E. Turonian – E. Maastrichtian (Upper CUCHE: E. Barremian – M. Albian (Lower Cretaceous)
Cretaceous)
LENGUA (Gr 1): M-L. Miocene HERRERA (Gr 7a ): M. Miocene HERRERA (Gr 7d ): M. Miocene LOWER CIPERO : E. GAUTIER: M. Albian – M. Cenomanian (Lower-Upper Cretaceous)
Oligocene

W
• Acquired and processed by Halliburton Geophysical for Exxon Trinidad Ltd and SBC partners in 1991 • 9 geophones per string, 2 geophone strings per group, array equally spaced. Fold coverage – 60
• Symmetrical split spread. Total Line length 21km. • Processed using standard Promax processing with AGC and predictive decon to remove multiples,
• 20m hole depth, 15lb charge size. 240 channels, sample rate 2ms. 30m receiver station interval , noise and spiking
60m shotpoint station intervals • There is risk of sideswipe artefacts
 Trinidad – ‘the graveyard of geologists’

• First oilwell drilled by the American Merrimac Company in

1857 at a depth of 280ft but was not commercially viable.
• Some 13000 wells have been drilled, producing just over
3.5BBO and 12TCF Gas, primarily from Pleistocene to Late
Miocene deltaic sandstones.

Southern Basin Consortium

• In 1989 Exxon, Total, Chevron, Trintoc and Trintopec come
together to form the Southern Basin Consortium to explore the
southern part of Trinidad for structures similar to El Furrial.
St. Croix
• Three wells were drilled onshore –St. Croix-1, Rocky Palace-1
and Iguana River-1. All wells tested Cretaceous fold structures.
Iguana River
Rocky Palace
• The wells penetrated Cretaceous sandstones, modeled by
Exxon to be deep water turbidites, encased in shales.
• All sandstones demonstrated residual oils or sub-commercial
accumulations.
• The St. Croix-1 well encountered Cretaceous shales that were
mature. The shales at Rocky Palace-1 and Iguana River-1 were
shown to be thermally immature as a potential source rock.
Leon Aden and Robert Bierley Exxon Exploration Company Houston USA;
Structural Development of the Southern Basin, Onshore Trinidad:
Implications for Hydrocarbon Entrapment
 2000
2015
2013
2012
2010
2009
2007
2005
2004
1995
2019
2016
2008
2006
2003
2002
1996
2014
1998
2018
2017
2001
1999
1997
2011
Following the basin-wide Cretaceous
exploration drive by Exxon and partners,
numerous Mid-Miocene targets were
identified through the use of the SBC 2D
Seismic.

In 1998 Petrotrin drilled their first and

last 100% operated onshore exploration
well – Puzzle Island

Mid-Miocene targets were marketed by

Petrotrin & MEEI attracting Vintage
Petroleum to take the risk at Carapal
Ridge and Corosan in 2001.

3D seismic was acquired for Talisman

and a 4 exploration well campaign
commenced in 2005 targeting primarily
Cretaceous, but also Late Oligocene and
Mid Miocene reservoirs.

Zaboca BGTT acquired 3D seismic across Central

Shandon Beni
Tamarind
Shandilay Block before drilling Corosan NE and
Ah Yah Yie Baraka East in 2007.
Cascadura
Barakat
Mapepire
St.
Cribo Croix Coho In 2008, guided by 3D seismic a deep
Corosan Corosan NE Mid-Miocene test was attempted in
Baraka East
Baraka
Puzzle Island SWP by TED with FRM-1 but they failed
Carapal Ridge to reach the target.
Saunders Iguana River
Firecrown Relinquished parts of the Central Block
Green Hermit
Rocky PalaceSnowcap 3D was then used to guide and de-risk
Jacobin the Firecrown, Snowcap and Green
Hermit Mid-Miocene discoveries.
FRM
Habanero 2015-2018 saw no onshore exploration
 Trinidad Onshore Bid Round 2013

Formerly Talisman / Petrotrin

Eastern Block 3D

Rio Claro Block

73,029 acres

British Gas / Petrotrin

Central Block 3D

Ortoire Block
40,756 acres
NWD 3D Seismic Survey
Petrotrin
St. Mary’s Block
43,880 acres

Exxon/Petrotrin
SBC 2D Seismic (1990’s)
 Why Explore an ‘explored’ basin?
Current facilities and infrastructure
 Majority of wells drilled in the 1940’s to late 50’s. are underutilized. Easy market of
 Biostratigraphy at its infancy and turbidite sandstone models were unheard of hydrocarbon and lots available
 Logging tools had very limited vertical and horizontal resolution workforce
 No 2D or 3D seismic at that time
 Lack of understanding of the kinematics in the deformation of shale rich stratigraphy
 Gas was seen as a nuisance and usually overlooked.

What tools do we need to get it right this time?

 Region scaled mapping and application of analogues
 Strong Structural Geology background is a necessity:- overprinting of multiple phases of deformation, Mid Miocene
sandstones are now understood to be syn-kinematic. As such both syn and post depositional tectonism has to be
fully unravelled.
 A determined, highly optimistic but pragmatic team – Exploration Onshore Trinidad has had its toll on many a
company and with more failures than successes in the last 20yrs a cloud of negativity has hung over many parts of
Southern Basin for a long period of time.
RIO CLARO BLOCK
 AYY – BARAKAT Conceptual Model AYY-1 Barakat-1

Drilled two exploration wells in Rio Claro Block todate,

both wells targeting the Mid Miocene Herrera
turbidites:
Sheet 1
Shaley Roof
1. Ah Yah Yie – 6220 TD Thrust
2. Barakat – 7400 TD

Ah Yah Yie was dry.

Sheet 2
‘Balata East’
Barakat has indications of a significant oil pool along
the Aloha Trend from Bouvallius in the east to Balata Early Miocene
Central to the west. Sheet 3
‘Aloha’
A future well will test the ‘Spurious Trend’ which is a
Late Oligocene Nariva sandstone play
AYY – BARAKAT Conceptual Model
Sheet 1 – ‘Shaley Roof Thrust’

Ah-Yah-Yie-1
1200 2200
2000 BE-17
BC-1 Barakat-1
BC-3 NP 3000
NP NP

BC-4 BC-5 NP
BC-2
AYY – BARAKAT Conceptual Model
Sheet 2 – ‘Balata East’ sands

Ah-Yah-Yie-1
NP 4800
4500 BE-17
BC-1 Barakat-1
BC-3 4500 5300
4600 4300

BC-4 BC-5 5500

BC-2

Plunge 10-15o
AYY – BARAKAT Conceptual Model
Sheet 3 – ‘Aloha’ sands

Ah-Yah-Yie-1
NP NP
5800 BE-17
BC-1 Barakat-1
BC-3 NP 6700
NP
NP
BC-4 BC-5 6900
BC-2

Plunge 10-15o
ORTOIRE BLOCK
 Exploration Methodology - Existing Wells

Well stock ~ 30 wells to start, ended up with 77 wellbores, 73 surface locations including an entire field of 22 wells unknown to
the MEEI at this time!
 COHO-1
1st Exploration Well
CO-85 (Catshill-85) was spud by Shell in August 1958, and drilled a normal succession encountering the
Gg7 Karamat at 5025, Top Herrera sandstones at 5440ft. The well penetrated a backthrust fault around
7400ft and entered subthrust Herrera sandstones. At approximately 10975ft the well penetrated a south
verging thrust and entered Karamat with Cipero affinities. It was approximated that to encounter the Herrera
sandstones again will require another 1000-1500ft of drilling. TD was called at 11055ft. No production tests.

Shell’s thinking at
the time was that
CO-85 did not drill
through any thrust
faults but rather
drilled a very thick
Mid Miocene unit
~3500ft

Dips from Karamat into Herrera interval all show a strong south easterly azimuth. Dip magnitude increases
from 10o near top Herrera to a max of 78o at a depth of 7304ft (in vicinity of backthrust). Dips are generally
south and south east thereafter until they switch to a northerly azimuth below the south verging thrust.
FO-1 (La Fortitude-1) was spud by Shell in April 1959, and drilled a normal succession, encountering the
Gg7 Karamat at 5555, Top Herrera sandstones at 8155ft, with TD at 10705ft in Gr7d Herrera shales. Dips
within the Karamat to Herrera interval all share a north westerly azimuth. No production tests.

Shell’s thinking at
this time is that
there is a large
northward dipping
SW-NE trending
normal fault
between CO-85
and FO-1
COR-1 (COROSAN-1) was spud by Vintage Petroleum (later Vermillion) in June 2001 using Well Services
Rig 15. COR-1 drilled a normal succession encountering the Gg7 Karamat at 5147, Top Herrera
sandstones at 5277ft, with TD at 7520ft within Gr7d Herrera shales.

Based on 2D
Seismic Vintage
saw an easterly
dipping normal
fault up-plunge of
CO-85

Six DST’s were performed.

Test 1 – 7093-7103 – flowed 98.2bbls water with gas
Test 2 – 5965-5975 – flowed 40bbls water with gas (15-20000ppm)
Test 3 – 5760-5768 – flowed 4.4mmcf on 20/64” at 2853psi with 385bbls water per day (15000ppm)
Test 4 – 5500-5516 – flowed 3.7mmscf on 20/64” at 2830psi with 300bbls water per day (15000ppm)
Test 5 – 5240-5252 – flowed 799bbls water on 20/64” at 1239psi (20000ppm)
Test 6 – 5216-5226 – flowed 100bbls water in 5hrs on 20/64” at 603psi (15000ppm)
COR NE-1 (COROSAN NE-1) was spud by British Gas in January 2007 and drilled a normal succession
encountering the Gg7 Karamat at 6990, Top Herrera sandstones at 7380ft, with TD at 9149ft still within the
Herrera sandstones. No tests conducted. All sands were interpreted to be wet with residual hydrocarbons.

Based on 3D
Seismic BGTT
targeting the
downthrown
eastern
hangingwall but
unfortunately did
not find a suitable
trap
Penal/Barrackpore/Balata Anticline Corosan ‘pop up’ Carapal Ridge Anticline Catshill Anticline Lizard Anticline

6d unconformity
Top Cruse

Lower Cruse

Lengua Relooking at the

2D seismic. TETL
7a Herrera
concept is a fold &
7bc Herrera thrust belt with
localised ‘pop up’
structures. In each
‘pop up’ structure
the underlying
footwall either has
not been drilled or
has been drilled
Fortitude Sheet down plunge
COHO-1: DIP CROSS-SECTION
COHO-1

N
W SE

Fault D

Fault C

Fault E

Fortitude Sheet
Fortitude Sheet
COHO-1 Perspective
 Cascadura
CAS-1
2nd Exploration Well

BW-3
BW-1

BW-5

BW-9

TETL’s CAS-1 is on trend with the Balata Anticline and the LOL’s
exploration well Barakat-1. Both companies evaluated their areas
separately and came together to ‘peer review’ models and concepts. And
interestingly both companies arrived at the same structural and
depositional model.
Balata West Area

Shaley Sheet 1

Sheet 2 produced oil in BW-5

Sheet 3 possibly overturned –

never tested Overturned?
Why Explore an ‘explored’ basin?
 It is only ‘as explored’ based on when it was explored - the models were only as good as the data and mapping techniques
available at the time.

 In areas with overprinting of multiple phases of deformation it is quite easy to ‘miss’ or mis-understand depositional
fairways, trap geometry and sealing capacity.

 A determined, highly optimistic but pragmatic team is required to push ahead despite the surrounding failures

 Good things come to those that keep trying…new things..

Thank you!