Hydrocarbons in igneous rock of Brazil: A review

Igneous rocks are widely developed in many hydrocarbon-bearing sedimentary basins in Brazil, and some igneous rocks play positive roles in the oil and gas accumulation process. But so far, no industrial oil or gas flow is discovered in igneous rocks in Brazilian onshore basins. At present, in some literatures published by some researchers, cases of igneous reservoirs in Brazil are inaccurate. The lithology of reservoirs in the Igarape Cuia oil and gas field, the oil and gas field of Urucu and the Barra Bonita gasfield, were previously thought to be volcanic rocks, but now are clastic rocks according to studies, and the igneous rocks in these three oil and gas field can only be acted as indirect and direct cap rocks. Furthermore, igneous rock reservoirs in the Campos Basin and Santos Basin in the Brazilian offshore are briefly analyzed. The representative Badejo oilfield in the Campos Basin has igneous rock reservoirs dominated by basalts which are intercalated with thin layers of volcaniclastic and sedimentary rocks, the storage space are vesicules, fractures and vugular pores, and the porosity of hydrocarbon bearing interval basalt reservoirs ranges from 10% to 15%. In addition, for the Santos Basin, igneous rocks in this basin are dominated by basic rocks, some alkaline intrusive rocks develop good micro spaces, mainly crystal moldic pores, inter- and intra-crystal dissolution pores and fractures, better reservoir intervals are often concentrated such as at sections near to unconformity surfaces and can have porosity of 6%–9% or higher; local pre-salt igneous rock reservoirs in the Santos Basin have the necessary conditions for hydrocarbon accumulation and it will be a new target layer for hydrocarbon exploration.