Colombia Continues To Yield Major Oil, Gas Discoveries

Carla Ketner McGettigan
I.E.D.S. (USA) Inc.
Houston

David G. Hunt
Consultant
Houston

• Colombia's Basins [503016 bytes]
• A look at Colombia's Drilling, Exploration [1266216 bytes]
• Llanos Basin Stratigraphic Column [59602 bytes]
• Upper Magdalena Valley Basin [76253 bytes]
• Putumayo Basin Stratigraphic Column [51487 bytes]

Colombia, where petroleum development began in 1908, is still yielding giant and supergiant discoveries. Recent successes result from improvements in exploration technology, in infrastructure, and in terms of participation offered by the Colombian government.

Total hydrocarbon exports, including coal, surpassed coffee in 1990 and now account for about one third of Colombia's total export earnings.

Colombia has 13 sedimentary basins covering an area of 700,000 sq km out of a total country area of 1,350,000 sq km, including the continental shelf. This article highlights four of the seven basins currently productive in Colombia, providing an overview of geology and recent exploration activity.

Geological setting

Before the uplift and deformation of the Eastern Cordillera of the Colombian Andean mountain system, three basins-Llanos, Putumayo, and Upper Magdalena Valley-were unified with the same sedimentary evolution from the early Paleozoic.

There was nearly continuous paralic clastic sedimentation since the Middle Cretaceous, including deposition of the Senonian Villeta (La Luna) world-class source rocks responsible for most of the oil in northern South America.

Llanos basin

The Llanos basin covers approximately 200,000 sq km of low-lying savannahs that serve as a catchment area for the Rio Meta, which flows northeast and joins the Rio Orinoco in Venezuela.

Llanos is one of a series of sub-Andean foreland basins that extend from Argentina to Venezuela. All of these basins are located just east of the Andes and characterized by an eastward driven thrust at the mountain front, a deep basin immediately to the east, and a gradual thinning of the sedimentary sections onto the shield areas.

Sediments in the Llanos basin and the adjoining thrust belt were deposited in a back-arc basin in the Late Mesozoic that became a foreland basin with the development of the Andes in the Middle Tertiary. The stratigraphic succession ranges from Paleozoic to Recent. The Late Cretaceous and Early Tertiary are of economic importance. This section includes alternating sands and shales deposited in alluvial, deltaic, and occasionally deepwater environments. The primary reservoirs are the Upper Cretaceous Guadalupe, Paleocene Barco, and Eocene Mirador formations.

Exploration activity surged in the Llanos basin during the 1980s due to attractive financial terms offered by the government. Elf, Ecopetrol, and Intercol made several discoveries. But it was the 1983 Cano Limon field discovery by Occidental that moved the Llanos basin to center stage of the international exploration arena.

The giants

Cano Limon field lies in the northern Llanos basin near the Venezuelan border in Occidental's Cravo Norte block. It covers approximately 37 sq km and produces 29°-30° gravity oil from deltaic sands in the Mirador formation at depths averaging 7,500 ft. Some wells are capable of producing in excess of 10,000 b/d of oil. The reservoir has an average porosity of 25% with permeabilities of several darcies and reserve estimates slightly in excess of 1 billion bbl of oil.

Occidental continues drilling operations in Cano Limon field and reported production of 203,363 b/d for March. Over the past year, approximately 20 development wells were successfully completed on the Cravo Norte block, and total oil production for 1995 was reported at 71.6 million bbl.

In 1988, British Petroleum (BP), Total, and Triton Energy completed the Cusiana 1, discovery well of another supergiant field in the Llanos basin. It is located in the Llanos foothills in the Santiago de las Atalayas association contract of the Casanare province.

Cusiana field produces light oil, gas, and condensate from the Guadalupe formation and Barco and Mirador sandstone formations in a thrust-related anticlinal trap at depths averaging 15,000 ft. Reserves for Cusiana are reported as 1.5 billion bbl of liquids and 3.4 tcf of gas.

This success was followed in 1992 by discovery of Cupiagua field on a separate structure in the same association contract area and within 15 km of Cusiana. Cupiagua reserves have been estimated at 500 million bbl of oil.

The most recent discovery was the Cupiagua K-5, completed Mar. 12. From Barco intervals between 15,626 ft and 16,760 ft, the well flowed a combined rate of 8,640 b/d of 39° gravity oil and 31 MMcfd of gas through a 1 in. choke. An additional oil-bearing thrust sheet was encountered below the presently developed field. This lower plate extends the oil column to 5,508 ft, the thickest in the country and one of the largest in the world.

BP spudded the Cupiagua E-7 outpost exploration well last Nov. 7 and completed it Apr. 30 after drilling to TD of 19,010 ft. To date, this is the deepest well drilled in the field, and test results have not yet been reported. Participants in the Santiago de las Atalayas association contract include BP with a 19% interest and partners Ecopetrol 50%, Total 19%, and Triton 12%.

During development of the giant Cusiana and Cupiagua oil fields, 180,496 b/d of oil was pumped during March 1996. During 1995, the Santiago de las Atalayas block yielded a total of 43.2 million bbl of oil.

Other Llanos activity

Nearby, Ecopetrol is drilling the Coporo 1 exploration well in the Medina reserve area. Targeting the Mirador formation, the well is projected to a depth of 18,200 ft and had reached 15,050 ft in June. The location is 80 km southwest of Cusiana field. Ecopetrol has described it as a match to Cusiana, touting potential reserves of 1.3 billion bbl of oil.

Further south, Chevron recently drilled the disappointing Anaconda 1(ST) in the Rio Blanco block of the Meta province. With partner Overseas Petroleum & Investment Corp. (OPIC) of Taiwan, Chevron began exploration on this association contract area in 1995. Seismic evaluations indicated hydrocarbon potential half the size of Cusiana, some 120 km to the northeast.

The well was sidetracked twice and reached a TD of 16,444 ft. Chevron reportedly spent $28 million, only to plug and abandon the well in May 1996 after three zones tested dry with only minor shows. Chevron and OPIC plan to continue exploration activities in the Rio Blanco block.

Previous success in the Llanos basin includes the Volcanera 1 discovery by Maxus in September 1993. The following November, BP acquired a majority interest in this Rector block.

In August 1994, BP commenced exploratory drilling on its Piedemonte block (100%) approximately 12 km to the northeast. The Florena A-1 and Pauto Sur B-1 were completed in October 1995 as oil and gas discoveries producing from the Guadalupe, Barco, and Mirador formations. BP announced combined reserves of 750 million bbl of oil and 5 tcf of natural gas in addition to the previously established estimates for the remarkable Volcanera discovery of 250 million bbl of condensate with 5 tcf of gas.

Drilling continued on the Rector block during March and April 1995, when BP spudded the Volcanera C-2 and the Dele B-1, respectively. The Volcanera C-2 was suspended on May 21 after it was drilled to 19,142 ft, and the well was being evaluated. June 1996 reports also indicate the Dele B-1 was drilling below 18,890 ft, targeting the Guadalupe and Mirador formations.

In the same province and directly to the east, Kelt Colombia SA has successfully completed five exploratory wells since August 1995 on its Casanare and Yalea blocks. Located near Elf's 1974 Trinidad 1 discovery, Trinidad 6B, 8, and 10 were completed in April and May 1996 with TDs averaging 10,000 ft and initial tests of about 2,700 b/d each of 33° gravity oil from the Tertiary Carbonera formation.

Upper Magdalena Valley basin

The Upper Magdalena Valley basin lies between the Central and Eastern Cordillera of the Colombian Andes. The basin is classified as an intermontane or successor basin to a much larger basin that included the Putumayo and the Llanos. Its present configuration resulted from the emergence of the Eastern Cordillera during the Andean orogeny.

The thick, organic-rich La Luna formation of Cretaceous age provides world-class source rocks for the basin and its abundant discoveries. The principal reservoirs are paralic sands of the Upper Cretaceous Monserrate and Guadalupe formations and the Caballos formation sandstone of Middle Cretaceous age. Traps are structural and structural-stratigraphic, related to both eastward and westward driven thrusts associated with the Central and Eastern Cordillera, respectively.

The first field, Ortega, was discovered in 1951 by Texaco. In the 1980s, further discoveries were made, principally by Tenneco (now British Gas), and a new pipeline linked the area to refineries in northern Colombia and export terminals.

Recent activity in the Upper Magdalena basin includes American International Petroleum Corp.'s (AIPC) drilling on its Lagunillas and Puli association contract areas with successful completions in the Chigsa 1 and Toqui-Toqui 32. Both wells produce from the Eocene Doima formation. The Toqui-Toqui 34 was a 1996 deeper pool test that flowed 124 b/d of oil from the Eocene Chicoral formation.

Toqui-Toqui field was discovered in 1986 with the Toqui-Toqui 1A exploration well drilled to TD of 2,700 ft. Field reserve estimates were reported at 44 million bbl of 22°-27° gravity oil and 15 bcf of natural gas.

South of the Puli block is Lasmo's Espinal association contract, where the Revancha 2 exploration well, targeting the Guadalupe formation, was suspended in November 1995 after testing at a final depth of 6,311 ft. The Revancha 1 discovery in 1994 followed Lasmo's earlier success on the license with the Venganza field discovery in 1992. The Venganza 1 well, drilled to TD of 6,790 ft, tested 22° gravity oil from two Guadalupe intervals at rates of 2,800 b/d and 3,000 b/d.

In April 1996, production from neighboring Purificacion field was reported at 4,000 b/d from two wells. Lasmo is planning a seismic survey to identify further prospects on the block.

In the adjacent Cucuana block of the Tolima province, Geopozos spudded the Guasimo 3 last Feb. 18. This new-field wildcat is targeting the Guadalupe formation and was reported at 2,544 ft in June 1996. The Guasimo 1 was suspended in November 1995 after being drilled to 4,021 ft and testing 15 b/d of 24° gravity oil from an unidentified interval.

Near the southern end of the Upper Magdalena Valley basin, Braspetro on Feb. 28 completed the Rio Ceibas 7 appraisal well on its Caguan block. The well penetrated Miocene Honda formation sands and tested 228 b/d of 24.7° gravity oil through a 1 in. choke. This was the first exploratory well to be drilled in the Caguan association contract area since the July 1995 transfer of 20.8% interest from former operator Esso. The remaining interest is shared by Ecopetrol 50%, Sipetrol 25%, and Total 4.2%. Esso discovered Rio Ceibas field in 1988. Braspetro plans further development on the block.

Putumayo basin

The Putumayo basin covers 48,000 sq km and is separated from the Llanos basin by the Guaviare arch. It is an extension of the Oriente basin in Ecuador. Discovery in the 1950s of Orito field by Texaco led to giant field discoveries in Ecuador.

Most Putumayo basin production comes from the Caballos formation, a basin-wide shallow marine sandstone. There are secondary objectives in deltaic sandstones of the Cretaceous Villeta formation and in the Eocene conglomerate of the Pepino formation. The western side of the basin has thrust-related faulted anticlines, while the eastern flank contains low-relief fault closure and combination structural-stratigraphic traps against the Guyana shield. Several discoveries in Ecuador near the border could extend into Colombia.

Exploration activity in the Putumayo basin is primarily focused in the Santana B block, licensed to the Colombia subsidiary of Garnet Resources Corp., Argosy Energy. The Esperanza 1 exploration well was abandoned as dry on May 2, 1995, at a TD of 7,129 ft. The well was drilled directionally to the southwest of the surface location to evaluate additional potential of the Villeta formation U and T sands and the Caballos formation.

The Palmera 1 wildcat well, spudded on Jan. 23, reached a TD of 8,836 ft and was dry. The well encountered the Villeta formation objectives; however, two zones were water-bearing, and a third sand yielded noncommercial heavy oil. Structurally complex anomalies exist in this unexplored northern portion of the Santana B block. Palmera 1 targeted a seismically defined trap in the Andes foothills.

Following the discovery of the Toroyaco, Mary, and Linda fields in 1990 and Miraflor field in 1991, subsequent efforts in the association contract area have been unsuccessful in establishing new potential. However, Argosy is reportedly planning a 3D seismic acquisition program in 1996 near the Mary and Miraflor field areas. Total 1995 production from the Santana B block was reported at 2.1 million bbl of oil and 9.15 MMcf of gas.

Middle Magdalena Valley basin

The Middle Magdalena Valley basin, Colombia's oldest producing province, covers approximately 30,000 sq km. The basin is a half graben in a long, narrow valley between the Eastern and Central Cordilleras. It is distinctly asymmetric, with rocks of the Central Cordillera dipping eastward under the westward-driven post-Miocene age thrusts from the Eastern Cordillera.

Fluvial channel sandstones and conglomerates in Paleocene to Oligocene formations are the principal reservoirs. These molasse sediments have porosities in the 20-25% range and permeabilities of 500-1,000 md. For many years, Colombia's largest field was the La Cira-Infantas with a cumulative production in excess of 800 million bbl of oil.

The abundance of hydrocarbons is directly related to the presence of La Luna formation source rocks. The formation is hundreds of meters thick and has a total organic content (TOC) of 3-4%.

Triton continues exploring in the El Pinal association contract. The 1992 and 1993 La Liebre 1 and 2 discoveries both tested oil in the Eocene La Paz formation. The La Liebre Deep 1 well was temporarily abandoned in January 1995 after penetrating the Oligocene Esmeraldas formation sands.

Following the reevaluation of test results, Triton spudded the Yumeca 1 well in April 1995. Located along the eastern edge of the Middle Magdalena basin and drilled as a tight hole, the well evaluated a large anticline developed beneath a fault detachment with prospectivity in the Cretaceous section. The well reached a TD of 13,664 ft and was abandoned with shows in September. Triton had been seeking partners to participate in future delineation drilling on the block. In March, Deminex farmed in for a 50% working interest, subject to Colombia government approval. The Yumeca 2 well was scheduled for this month.

Farther south, the Opon association contract area is located in the Santander province of the Middle Magdalena basin. Amoco (60%) with partners Hondo (30%) and Opon Development Company (10%) plan to acquire 3D seismic to guide further development drilling subsequent to the Opon 3 and 4 gas discoveries.

Following successful testing of the 1994 Opon 3 well, the Opon 4 was spudded in February 1995, reached a TD of 11,500 ft, and was temporarily abandoned as a gas and condensate discovery in November 1995. The well tested 1,900 b/d of condensate and 54 MMcfd of gas from the Eocene La Paz formation and was reclassified as a deeper pool wildcat. Amoco's 2D seismic program commenced in late 1995 and is nearing completion.

GHK's Dindal association contract area in the Middle Magdalena basin contains the Emerald Mountain prospect, a seismically controlled structure with approximately 57 sq km of mapped closure. The El Segundo 1 wildcat well was spudded in December 1995 and will be completed as an oil producer after reaching TD of 5,718 ft and testing 300 b/d of oil in February. Production tests continue in order to establish potential production rates and pressures of this uppermost section of the Cimarrona formation in the upper Guadalupe group. Reports indicate that production facilities are being installed to produce 5,000 b/d of oil. Appraisal drilling is planned for mid-1996. Other partners on the Dindal association contract include Seven Seas Petroleum and Sipetrol.

Future activity

The state oil company is offering two promising exploration areas in the Llanos thrust front to 17 companies. The following companies pre-qualified to participate in Ecopetrol's auction: Shell, Exxon, BP, Amoco, Arco, Ampolex, Braspetro, Canadian Petroleum, Chevron, JNOC, Lasmo, Maxus, Mobil, Occidental, Repsol, Texaco, Total, and Elf.

Located near Cusiana and Cupiagua fields, the areas could contain total reserves of 720 million bbl of oil.

The Torcoragua structure covers 30 sq km and is located in the Llanos basin's San Lope block. Reserves are estimated at 500 million bbl of oil. The Troyano structure covers 49 sq km in the Putumayo basin's San Juan block with estimated reserves of 220 million bbl of oil.

Data packages were available Apr. 9. Ecopetrol recently extended the bidding deadline from July 9 to Aug. 21. Winning bids will be selected on the basis of maximum production share to Ecopetrol, probably more than 50%. Furthermore, Ecopetrol will retain operatorship while the participating companies fund 50% of the drilling costs.

The Authors