PREFACE

 

Early in August 1997, during the preparatory meeting of an International Symposium on the Geology and Mineral Resources of Madagascar within the frame of Gondwana, the late Professor Albert Rakoto Ratsimamanga, a prominent Malagasy savant, a corresponding member of the French Academy of Sciences (Institut de France) urged me strongly to put down in writing my thinking about the petroleum potential of Madagascar. Now, nearly ten years later, and at a time when several foreign oil companies are actively engaged in oil exploration in Madagascar, I think it right to defer to that wish. The present book, titled "Forecasting  Hydrocarbon Discoveries in Madagascar : An Application of the principles of the Moody and Hill System of Wrench Fault Tectonics," is the outcome of more than 25 years field experience and research studies in the petroleum exploration domain, mainly in Madagascar.

 

Many years ago, sometime in June 1973, when I worked with Continental Oil Corporation's Madagascar affiliate, the thought occurred to me that there were striking similarities between the profiles of  two geological cross-sections of the North Sea, drawn by Dr Robert E. KING (Fig.41 in the September 1972 issue of World Oil), and that of the N-S cross-section of the Morondava Basin post-Karroo by J. BAUER (Société des Pétroles de Madagascar, 1958). So, I formulated the hypothesis that there may be two petroleum hinges in the Morondava Basin, respectively in the post-Karroo and the Karroo formations, which I incessantly looked into from then on.

 

The idea aroused the then acting chief executive of CONOCO Madagascar, Robert G. BERTAGNE, to such an extent that he enthusiastically stated: "President Tsiranana won your political independence, but you struck pay dirt that might open the gates to your economic independence. The existence of these hinges is a real asset as to the pursuit of petroleum research in Madagascar; and I must confess that without a flair (the "seventh sense")-that essential prerequisite for any researcher- you couldn't have detected such similarities".

 

From that time on, I focused all my attention on that "pay dirt". By applying to Madagascar the principles of the Moody and Hill system of wrench fault tectonics, I advanced the theory that Madagascar tectonics may have evolved through a succession of several en echelon complementary first order wrench faults which belong to the pre-Hercynian and post-Hercynian, in particular the Bongolava axis, on the eastern edge of the Morondava Basin (Fig.21).

Taking into account (1) that hypothesis about Madagascar tectonic evolution, (2) the N-S cross-sections of the Morondava Basin, (3) the fact that the western flank of Bongolava hosts the important accumulation of  Bemolanga bituminous sandstones and that of the Tsimiroro heavy oil, and (4) that the same causes produce the same effects, I concluded that the western flanks of all the complementary 1st order wrench faults could play the same role  as Bongolava. This  reasoning originated the figure 25 in 1980 and the areas selected by Amoco Co. and Occidental Petroleum Co. in 1981.

 

The analysis of the unsuccessful exploratory drillings conducted by AMOCO and OXY between 1984 and 1986, on the one hand, and the finding of shows of light oil in the Cretaceous formation of Manambolo 1 by AMOCO, confirming those resulted from previous drillings by CONOCO and Chevron Oil Co. on Serinam, on the other hand, both led me to think that, if one looks into  the possibility of finding an oil accumulation in the Cretaceous, then WEST MANAMBOLO, which AMOCO ranked only at the 5th position, appeared to be the most promising prospect for drilling. This conclusion was definitely buttressed by  the discovery of the first gas field in Madagascar in the last quarter of 1987 after PETROCANADA agreed to finance a sole risk exploratory drilling undertaken by OMNIS, the Malagasy state organization in charge of hydrocarbon research: two drill-stem tests flowed gas at a total rate of 446,000 Cubic Meter(m³) per day (16 MMscfpd) while reserves were estimated at 1,800 Million cubic meter (63,566 MMscf)

 

In 1979 Jan Raican, a Rumanian geologist from UNDP then working as a consultant with OMNIS, tipped me off that the first Rumanian oil field was found in traps of a  "broken porcelain plate"-like type after years and years of fruitless research. Furthermore, if we consider (1) the results of Occidental's drillings on the lower Sakamena (Permian) which indicate that the light oil shows were insignificant while the reservoirs were of poor porosity, and (2) the principles of the Moody and Hill system of wrench fault tectonics which implies that the drag folds and the high zones of the pre-Hercynian have been in motion again during the post-Hercynian, we could assume that this replay have fractured and fissured the reservoirs, and improved their porosity on the top of the high zones.

 

That is why, as soon as 1986, and later in 1988, I recommended to pick out MANANDAZA -which is on the same parallel as MANAMBOLO-for an exploratory drilling to be performed in order to test the oil potential of the Lower Sakamena. Shell carried out two drillings on Manandaza in 1993 and found interesting light oil-shows (41° API) in the fissurations of the Sakamena reservoirs.

 

Finally, by taking into account

1)       the different factors such as: depth, measured (geothermic and geochemical) temperatures, paleotemperature and geothermic gradient, TOC (total organic carbon), S2 in ppm, and the convertibility rate of the source rocks, the porosity, permeability, and salinity of the reservoir rocks;

2)       the above theory on the tectonic history of Madagascar;

3)       the two N-S cross-sections of the Morondava Basin Karroo and post-Karroo,

 

and proceeding through elimination, I managed to reduce the extent of the petroleum zones of interest in Madagascar to approximately 45,000 km² (17,375 sq miles), that is, around 15% of her sedimentary basins and continental shelf (deep of sea < 200 m), the Cretaceous and the Permo-Triassic being the main targets. So,  if my hypotheses proved to be correct, it would ensue a considerable economy of time and money for companies interested in pursuing hydrocarbon research in Madagascar while their risks of encountering  dry wells should be fairly reduced.

 

Norbert Rabe

 

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