Exploring for gas: the future for Angola

Abstract

AbstractOffshore Angola is a world-class petroleum province with oil production in excess of 2 million barrels per day in 2008. Exploration activity in the offshore commenced in earnest in the early 1990s, with the contractual terms permitting only the production of oil. There is no provision for the production of gas. However, there have been several discoveries of associated and non-associated gas, by accident, in the search for oil. Gas will play a significant role in the future of Angola. A new gas business is emerging. Demand from a new liquefied natural gas (LNG) plant, the emerging Soyo industrial complex and the growing domestic and industrial sectors have created a business environment whereby near-term gas exploration, development and production is a critical need for the future of Angola. What is the gas resource potential of Angola: from mature basins to new frontiers? Is there potential for new giant gas fields? Conceivably, there are multiple petroleum system opportunities. This paper provides some insights into the petroleum geoscience exploration efforts being made by Angola's national gas company, Sonangol Gas Natural. The focus of this paper will be on the exploration for non-associated gas. The associated gas potential of Angola is relatively well known and will not be discussed. Sonangol Gas Natural has an extensive offshore seismic and well database. This is characterized by a series of merged, high-quality 3D seismic surveys that facilitate the application of the most advanced technologies. In excess of 130 offshore wells have encountered gas at multiple stratigraphic levels. However, the interior basins are a truly frontier province and data are limited to a regional gravity and magnetic dataset and surface rock outcrops. The conventional thermogenic petroleum systems of the offshore and the adjacent onshore Lower Congo, Kwanza/Benguela and Namibe basins are relatively well known. These comprise a Late Cretaceous and Cenozoic post-salt petroleum system, and an Early Cretaceous and Late Jurassic pre-salt petroleum system. The primary emphasis of the exploration effort in these basins is to better understand and to delineate the gas kitchens for the known source horizons, for example Malembo, Iabe (post-Aptian salt) and Bucomazi (pre-Aptian salt) formations. Biogenic gas plays constitute an unconventional petroleum system that requires different exploration concepts from those of conventional thermogenic petroleum systems. The principal challenges are to identify palaeo-gas hydrates, reservoired in Miocene clastics, to define the biogenic gas fairway and to evaluate the play elements of reservoir, trap and seal. The geological conditions necessary to establish a biogenic gas play in the deepwater and ultra-deepwater will be examined. The interior Owambo, Okawango and Kassanje Basins have no proven petroleum systems. However, some new play concepts of Neoproterozoic age will be presented using possible analogues worldwide. The future demand for gas will increase globally. New developments in LNG will change the world of gas. Angola will be a key player.