Wise explorers learn a lot from their dry holes. In the period of 1978 to 1982, Maraven S.A. drilled 15 wells offshore Venezuela, and none were economic. However, this exploration campaign allowed the company to collect a trove of invaluable geoscience data. Promising new ideas regarding the geology of the offshore region, as well as enhancements in future burial history and thermal maturation profiling can be anticipated as a result.
Venezuela has a long petroleum exploration history. The Mene Grande oil field was discovered in 1914 with the drilling of the Zumaque No. 1 well by the Caribbean Petroleum Company, the name used by Royal Dutch Shell. Later, several multinational oil companies operated in the country, including Gulf Oil Company (doing business as Mene Grande) and Standard Oil of Venezuela (Creole Oil Company), which operated throughout Venezuela until nationalization in 1975. Other multinationals such as Texaco, Mobil and Occidental were quite active there, as well.
Venezuela’s PDVSA is Born
Petróleos de Venezuela S.A. was created on Aug. 30, 1975. The next year, through the “rationalization” or merger of the many companies operating in the country, four subsidiaries, Maraven, Lagoven, Meneven and Corpoven were established. Two years later, the Venezuelan Ministry of Energy and Mines granted authorization to three of those subsidiaries, including Maraven, to carry out exploratory activities in areas outside its traditional, prolific hydrocarbon basins, located inland.
To achieve this purpose, a group of experienced petroleum professionals from PDVSA conducted extensive offshore studies. They reviewed many geological and geophysical publications and reports from regional work carried out in the 1960s and ‘70s at domestic and foreign universities, as well as articles published by professionals from the Venezuelan and international petroleum industry.
At the start of the program, the subsidiaries found themselves with a shortage of oil professionals to achieve their goals. After the nationalization, a sensible decision was made to sign technological assistance agreements with foreign major oil companies. They were jointly tasked with the employment and training of young Venezuelan geologists, geophysicists and engineers within the subsidiaries. Positive results of this effort allowed the exploration program to get started in 1978, and it was eventually completed satisfactorily.
Some of the most important publications in that period related to the geology/geophysics of the continental shelf, including Galavis and Louder (1971), Lattimore et al. (1971), Peters (1972), Feo Codecido (1973), Case (1974), Silver et al. (1972, 1975) and Bonini (1978). New 2-D seismic surveys were shot on the Venezuelan continental shelf. Geophysical interpretations made by a group of professionals from the different subsidiaries provided promising structural evidence for trapping hydrocarbons on the continental shelf areas in La Vela de Coro, in Golfo Triste, in the Tuy-Cariaco Basin and on the continental shelf off the Araya-Paria Peninsula east of Margarita. Based on these results, PDVSA was convinced of the offshore potential and budgeted $175 million to cover two years of this important exploration drilling program.
To achieve the search for and production of hydrocarbons in economic quantities, the offshore region was divided into three areas to be explored by three PDVSA subsidiaries. The program began with contracting three offshore drilling rigs equipped to drill in areas with depths less than 200 meters, the limit of the drilling technology at that time. Corpoven was entrusted with the Gulf of La Vela with a jackup rig. Lagoven was assigned the shelf off the East Coast between Margarita and Trinidad with a drillship. Maraven was given the region between Cabo Codera and Margarita Island, called the Tuy-Cariaco Basin, with a semi-submersible rig.
Of enormous help to the Maraven drilling effort on the shelf were publications from professors of the Universidad de Oriente in Cumana who had conducted oceanographic studies in the Tuy-Cariaco Basin. Some of these were Richards (1975), Maloney (1966, 1970), Febres and Herrera (1975), Herrera and Febres (1975), and Keller and Minter (1975).
Maraven’s Exploration Effort
The Tuy-Cariaco Basin, which covers approximately 36,300 square kilometers, is located between Cabo Codera and Margarita Island and between the Venezuelan coast and the strait between Margarita Island and La Blanquilla Island. This geological basin includes a northern continental shelf less than 200 meters deep that surrounds Tortuga and Margarita islands, called the North Margarita-Tortuga Shelf. It also includes the Cariaco Trench (1,400 meters deep), a continental shelf to the south named the Ensenada-Barcelona Shelf and one to the east named the Cubagua-Margarita Shelf.
From the beginning of the exploration program in the Tuy-Cariaco Basin, Maraven had at its disposal large volumes of useful geological information. It also had some 19,200 kilometers of 2-D seismic lines. These seismic surveys were carried out by Gulf Oil (1974), Teledyne (1975), Norway’s Geco Geophysical (1978) and Gulf’s Hollis Hedberg Oceanographic Ship (1980). This seismic dataset allowed Maraven’s geophysicists to perform detailed interpretations and to map several geological structures (anticlines and faulting) considered the most suitable for trapping hydrocarbons.
At that time, there was no geochemical data to determine the existence or absence of one or more hydrocarbon-generating source rocks. Based on updated, modern geochemical studies, more recent evidence indicates that Tertiary rocks (Pleistocene to Eocene) deposited above the Cretaceous basement in the Tuy-Cariaco Basin lack sufficient kerogen-rich organic material needed for significant hydrocarbon generation.
Detailed microscopic examination of foraminiferal fauna, observed in drill cuttings sent to the Caracas office every day by helicopter, provided real-time, stratigraphic-sedimentologic characteristics of the rock formations being penetrated. Later, petrographic, geochemical and isotopic analyses of the cores taken within clastic and limestone rocks and from the igneous-metamorphic basement, resulted in a better understanding of the geology and tectonic framework of Venezuela’s offshore continental shelf.
For example, isotope age analyses of the basement rocks from the Tuy-Cariaco Basin shelf area were performed by Teledyne Isotopes. They are presented here for the first time in English, in the public domain. Apart from being described in proprietary reports, most oil companies take no interest in them because basement igneous-metamorphic rocks neither generate, nor (generally) produce hydrocarbons. Importantly, the data give an idea of the sedimentary thickness (the depths shown) of the Tuy Cariaco Basin and the hydrocarbon basal limit that is the top of the Upper Cretaceous basement.
Maraven drilled three wells in Golfo Triste and 12 wells in the Tuy-Cariaco Basin, with the semi-submersible Ocean Rover that was owned by the drilling company, ODECO. The entire campaign was conducted with no time lost or serious accidents to regret. There was one scare when a geologist decided to spend the day at the top of the rig with the derrick hand during a drill-bit tripping operation, and no one knew where he was. It was feared he had fallen overboard until he showed up for dinner in the evening. Luckily, while he was missing, panic did not set in and everyone was happy to see him again.
Although evidence of hydrocarbons was observed in two of the wells, no accumulations of economic interest were discovered and no wells were completed for production. However, most of the assigned exploration goals of the program were fulfilled. This can be attributed to the well-trained technical staff dedicated to a high-cost, high-risk offshore exploration effort, with a well-equipped drilling rig for use on the continental shelf to a water depth of 200 meters. Today, offshore drilling technology has come a long way, drilling in water depths of 3,000 meters with much better equipment.
Based on the results of exploratory drilling in Tuy-Cariaco Basin, at the time and after 1982, Maraven professionals, in collaboration with those on loan from Shell Oil Co. and other companies, wrote a significant number of internal reports. The more important ones were Haak (1980), Haak and Pitelli (1981), Gallango (1981), Evans (1982, 1983), Jordi et. al. (1982) and Monsalve et al. (1984). With Gulf, Teledyne and Geco seismic data and geological information obtained from the wells, the first publications in international technical journals were Schubert (1982) and Goddard (1986). These publications describe previously unknown geological/tectonic aspects. More recently, using the same data, several important articles have been published, including a review of the structure and tectonosequences of the Cariaco Basin by Escalona et al. (2009).
Personnel and Their Jobs
Maraven’s magazine “Contexto” explained that at the end of 1975, Shell Oil of Venezuela had only 21 geologists on the payroll and in 1982, Maraven had 57 professionals in that discipline. This was the result of Marven’s awareness in 1978 of the shortage of specialized professionals, so the important task of searching for and finding suitable personnel began. Under the leadership of Hans Krause, the exploration manager (who would eventually go on to become the longtime editor of this very Historical Highlights section of the EXPLORER), they were able to form an offshore team with geologists, geophysicists, petrophysicists and petroleum engineers within the exploration and drilling departments. This was necessary to fulfill the immense task of exploring their assigned areas, the Golfo Triste and the Tuy-Cariaco Basin. The young professionals employed were placed under the guidance of more experienced hands, such as Luis (Toto) Rodriguez Salazar, who reviewed and approved the required geological and geophysical well proposals and was responsible for day-to-day offshore geological operations. In addition to the specialized courses the younger staff were given, an important part of the preparation was on-the-job training.
The experienced Venezuelan petroleum geoscientists and engineers carried out most of their work in the Maraven offices in Caracas, with occasional visits to the rig. Ovidio Suarez and his team of engineers, using state-of-the-art petrophysical software, were instrumental in detecting hydrocarbon indications on two of the wells drilled.
This large region of interest was divided into several areas (North Shelf, South Shelf, Cubagua-Margarita Shelf, etc.) depending on their geographic position around the Cariaco Trench. Maraven was fortunate to have on its team the very experienced geophysicist Harry Stenson, who was on loan from Exxon under the technological assistance agreements. Several geophysicists were fortunate to work with and learn from Stenson, including Marcos Roberto who performed 2-D seismic interpretation in area of the North Margarita-Tortuga Shelf using Geco and Teledyne seismic data. His work resulted in the location and drilling of three important wells.
To assist in the drilling activity on the Ocean Rover, young geologists and several engineers worked 14-day shifts on the rig, with seven days off. They performed their tasks under the supervision of experienced drilling engineers from Triton Engineers and professionals from ODECO. Perhaps the most uncomfortable situation during the 14 days of work was the lack of a normal routine. During the 24 hours, one could sleep just two hours or a full eight hours (and at any time of the day), depending on the activity being performed.
Foreign staff from several different countries worked 30 days in a row with 30 days off. Among these were experienced drilling engineers and skilled workers of every conceivable discipline (toolpushers, welders, mechanics, electricians, cooks, crane operators, etc.). Perhaps the most specialized workers were the divers, five of whom worked during each 30-day shift. Given the limited time requirements of their assignments, they spent most of their time not working – just eating and reading. Their function was to conduct an inspection of the seabed before drilling began. This job took only one day, but they had to stay on board for 30 days just in case there was an emergency that required their expertise.
Another particularly important group consisted of four specialists from the mudlogging unit of the French company Geoservices. These professionals were very well trained and worked two at a time in 12-hour shifts, 30 days on the rig. One of Maraven’s young geologists, Juan Francisco Arminio – the one thought to have fallen overboard – spent long hours working alongside the mudloggers, sampling and describing the lithology of drill-cuttings and analyzing the atomic absorption data for hydrocarbons. Their tasks also included monitoring all drilling parameters, and the cabin in which they worked was busy 24 hours a day. It was the heart of the operations, where engineers and geologists met to observe and to discuss details related to the progress of the drilling activity. Integrated teamwork was essential for the success of such a demanding offshore exploration project. At any one time, 50 to 60 people lived and worked on the rig.
Getting There: Difficult; Life Onboard: Comfortable
Helicopters and crewboats were used to transport personnel the long distances from land to the Ocean Rover, sometimes hundreds of kilometers offshore. The first heliport was located at Maiquetía airport, north of Caracas on the coast. It was later located on Margarita Island’s airport where the flight time to the most distant locations was reduced from two hours to one hour. To carry drilling materials and equipment for the drilling operation, large workboats were used. Both the crewboats and the larger workboats set out from the port of Baritinas (Pamatacualito) near Puerto La Cruz in eastern Venezuela. For example, a workboat trip from PLC to the MTC-1X well, a distance of 90 kilometers, took up to seven hours. The faster crewboats took about four hours to the farthest locations, sometimes over rough seas. The logistics involved with this offshore exploration program were demanding.
Life on the Ocean Rover rig, however, was quite pleasant. Both the food and the rooms were excellent and – without exaggeration – almost like a four-star hotel. The drilling operation was a 24-hour continuous activity, and the drillers and roughnecks worked 12-hour dangerous, strenuous shifts. There was food available 24 hours a day, prepared by top chefs. Most of the cabins were four-bedded with frigid air-conditioning, requiring warm bed covers to avoid catching a cold. In addition, there was a library, a game room, and another for watching movies. During their off hours, the staff had many ways to entertain themselves when not working, including the possibility of fishing if one wanted to go down a ladder about 40 meters to reach a small platform at sea level. The chefs cooked the fish caught for the entire crew onboard the Ocean Rover.
Accomplishments
More than four decades have passed since 1982 when Maraven completed the drilling phase that included three wells in Golfo Triste in the State of Falcón and 12 wells in the Tuy-Cariaco Basin. This landmark accomplishment indicates how a well-trained technical staff engaged in a high-cost, high-risk offshore exploration program was able to successfully accomplish the task assigned to them. Some geological aspects referring to the petrographic and geochemical results of the cores taken within the igneous-metamorphic basement were of great interest and contributed to a much better understanding of the offshore Venezuelan regional structural framework.
The results of the exploratory activities were successful from both a technical/operational and geological point of view. Presence of hydrocarbons was observed in two of the wells (MTC-1X, EBC-1X) but without accumulations of economic interest. Four years of exploration activity with only 12 wells drilled in an area as immense as the Tuy-Cariaco Basin was not sufficient to conclude that this basin does not contain economic accumulations of hydrocarbons. A future extensive exploration program, based on state-of-the-art 3-D seismic surveys and deeper drilling on the continental slope, targeting turbidite deposits, is required to properly define the prospectivity of the Tuy-Cariaco Basin.
Acknowledgements
I had the enormous pleasure of working as a geophysicist on the project alongside several excellent petroleum professionals who participated in this important exploration venture in the Tuy-Cariaco Basin. The hard work they delivered for the success of the program is the reason this historical event can be reported. Each of them deserves recognition and deep gratitude from the author. Matthew Silverman collaborated in the improvement of the article with his critical suggestions. Hans Krause, Maraven’s exploration manager who headed the program, gave suggestions and recalled situations that were of enormous value for this brief history.