Oil industry analysts and observers, both Angola-based and overseas, are closely watching a well testing programme underway in the Tobias oil field, located in the onshore Kwanza Basin, approximately 90 kilometres south of Angola’s capital city of Luanda.
This oil field has been inactive since it was abandoned in 1998 during Angola’s long civil war.
However, Sonangol – Angola’s state oil company and London-based Corcel Plc are attempting to bring life back into Tobias.
In the past half year they have drilled two wells, Tobias-13 and Tobias-14 in the Tobias field and have embarked on testing both wells. Should they be successful, this could lead to a sharply rejuvenated interest in other opportunities within the basin.
History of Exploration and Production in the Onshore Kwanza Basin
The onshore Kwanza Basin was the first basin in Angola to have undergone oil exploration and development. The first-ever well to be drilled for oil was in 1915 in the valley of the Dande River about 40 kilometres northeast of Luanda. Oil exploration occurred sporadically for the next four decades with no commercial success. The Belgium-based oil company Petrofina was the most active of the oil companies in the basin. Petrofina drilled Angola’s first commercial oil discovery at Benfica, near Luanda in 1955. Oil production commenced in the same year and eventually 80Million barrels of oil were produced from the onshore Kwanza Basin. The oil was delivered through a small diameter pipeline to the Petrofina refinery in Luanda. The company achieved maximum production in 1988 when it delivered 18,000Barrels of Oil Per Day (BOPD). About half of this oil was from eight fields which produced from the Lower Cretaceous-age Binga Formation limestones and the other half was from Miocene-age sandstones in the Quenguela North field.
Due to escalation of Angola’s civil war and the danger of attacks by the rebel faction UNITA, Petrofina stopped producing oil in 1998 and terminated all its field developments in the basin. Consequently, ten small oil fields remained unproduced or under-produced and eventually the fields fell into a state of disrepair. In the past half decade, a few bid rounds have taken place where several blocks were available for acquisition. Sonangol and some small Angolan oil companies and junior international oil companies are interested in rehabilitating the old oil fields using modern oil field technology. The Angolan companies have included Somoil, Simples Oil, Tusker Energy and Mineral One. Edmonton, Canada-based MTI Energy has also obtained operatorship and non-operatorship in a number of blocks in the onshore Kwanza and onshore Lower Congo Basins.
Re-development of the Tobias Oil Field
In the past year, a high-profile event has been the drilling of two wells in the Tobias oil field in 2023 by Sonangol and Corcel Plc. This has resulted in a much-heightened interest by oil companies in the onshore Kwanza Basin.
The Tobias field is situated onshore in the southern area of the Kwanza Basin. The field consists of 12 historic vertical wells drilled in the 1960s and 1970s by Petrofina. The discovery well, Tobias-2 was drilled in 1961 and discovered oil in the limestones of the Binga Formation. Tobias is structurally a deformed anticline approximately eight (8) kilometres long and 1 kilometre wide. The Binga in Tobias is a low porosity limestone with an average of 2.0% porosity but locally the matrix porosity can be in the order of 14%, according to legacy 1983 and 1991 publications by Schlumberger. Production is possible mainly because of the intense faulting and fracturing resulting from the folding of this structure. The Tuenza evaporites serve as the caprock.
Oil in the Tobias field has a density of 31 degrees API. The top of the reservoir is at a depth of 520metres (1,710 feet). The initial oil column was 350 metres (1,150 feet) and the bottom hole pressure was 53kg/cm2. Due to the intense natural fractures in the Binga, the initial oil production was high at 12,000BOPD by solution gas drive (Schlumberger, 1983). However, production dropped rapidly, and water injection was necessary to maintain production. Prior to Tobias being abandoned by Petrofina, the field produced a total of 29Million barrels of oil.
Corcel Plc has a 20% working interest (18% net) in Block KON-11 which is operated by Sonangol. Corcel is an Angolan – Brazilian oil and gas company focused on onshore upstream development as well as mining and mineral resources development. Corcel also has a 22.5% working interest in Kwanza Basin Block KON-12 and 31.5% in KON-16.
Corcel is an AIM-listed company. The Alternative Investment Market (AIM) is the London Stock Exchange’s (LSE’s) international market for small and medium size growth companies.
Corcel announced that Tobias-13, which was spud in September 2023 was drilled at a downdip location from historic production and reached its target depth of 959metres. Corcel’s press release mentioned that the full Binga reservoir section of about 120metres was encountered in the well as prognosed and intersected 80metres of Binga reservoir with several potentially productive zones in multiple intervals. Corcel stated that the results of Tobias-13 implies significant hydrocarbon potential remaining.
Tobias-14 was drilled directly after Tobias-13 to its target depth of 781metres. In a December 28, 2023 press release, Corcel said that Tobias-14 was located at the top of the Tobias anticlinal structure and is an offset to Tobias-4, the largest historic producer in the field, which produced 12,580BOPD at its peak, albeit penetrating only the first eight (8) metres of the reservoir. Tobias-14 penetrated a full Binga reservoir section of about 80 metres with identical zones encountered as in Tobias-13 and had oil shows throughout. Tobias-14 drilling encountered highly fractured oolitic limestones in the reservoir with good primary porosity values in the range of 4 – 14%. Corcel believes that the porosity is enhanced by the extensive, naturally fractured carbonate system. Initial pressure readings support Corcel’s predrill thesis that the reservoir has returned to its original pressure values through active recharge of the system. Tobias-14 found no presence of water despite Tobias-4 watering out at the end of its production life. Corcel believes that this indicates the field has been fully re-equilibrated.
Tobias-14 and Tobias-13 Well Testing Programme
In a February 12, 2024 press release, Corcel announced that testing of Tobias-14 has formally begun. Delays in the start of the testing have been encountered over recent weeks primarily due to longer than expected timelines for deliveries of required testing equipment, combined with severe inclement weather at the well location, which included heavy rains and regional flooding.
Once completed, the Operator, Sonangol will then move the test equipment to the Tobias-13 well pad, which is already being prepared for testing, and will conduct flow testing on the Tobias-13 well. Testing of both wells will determine formation pressures and ultimately the flow rates. Sonangol and Corcel believe the results will allow them to restart production via an early production system (EPS).
Various companies and oil industry analysts are closely watching the oil industry media for announcements on the Tobias wells testing programme. If favorable results are achieved, then this would send out the message that there is positive life left in the other old oil fields in the Kwanza Basin. This could start a stampede of companies exploring for oil in similar fields or focus on greenfield exploration.
It is evident that the investment community has high hopes for positive news from Tobias. One year ago, Corcel’s share price was 0.25 British pence per share. Their share price quadrupled to the current price of 1.0 pence.
Tako Koning is Holland-born and Canada-raised. He has a B.Sc. in Geology from the University of Alberta and a B.A. in Economics from the University of Calgary. He lives in his home city of Calgary, Canada. During his long career in the Canadian oil industry, he also lived and worked in Indonesia from 1980 – 1986, Nigeria from 1992 – 1995, and Angola from 1995 – 2015. He was employed primarily by Texaco and also by Tullow Oil (Angola Block 1/06) and Gaffney, Cline & Associates. He has driven through most of the onshore Kwanza Basin and had the opportunity to study the basin’s outcrop geology as well as visit some of the abandoned oil fields including the Tobias, Galinda and Quenguela North. He is pleased to share his knowledge in this article. For the past 23 years, he has been a member of the International Advisory Board of Africa Oil + Gas Report (AOGR) since it was founded in 2001 in Lagos, Nigeria by Toyin Akinosho.