Publication Date:
2003-01-01
Description:
Oil and gas fields in crystalline basement are discovered mostly by accident, usually when the well operator notices hydrocarbon shows and tests the well. However, as shown in this book, such reservoirs can be very prolific, especially if the basement rock is highly faulted or fractured (the Bach-Ho fractured granite reservoir, Vietnam, produced some 130,000 BQPD). The standard definition of crystalline basement by petroleum geologists is any metamorphic or igneous rock unconforroably overlain by a sedimentary sequence-. However, crystalline rocks need not be metamorphosed, nor significantly older than their sedimentary cover. Perhaps for a more appropriate definition of crystalline basement, we must again look to Landes et at. (1960): the only major difference between basement rock and the overlying sedimentary rock oil deposits is that in the former case the original oil-yielding formation (source rock) cannot underlie the reservoir'. As such, further exploration involving geological, geochemical and geophysical studies may lead to a significant revision of the definition and nature of basement rocks in a particular area, with the possibility of discovering hydrocarbon source rocks located stratigraphically within rocks previously regarded as basement. Examples of where hydrocarbons have migrated into older porous metamorphic or igneous rocks to form a basement reservoir include the volcanic reservoirs of Japan, the oil fields of Mexico and the Maracaibo Basin of Venezuela (see Schutter 2003). Although still often dismissed as exotic curios, this may be a mistake. A case in point (discussed in Koning 2003) is the Suban field, southern Sumatra. Prior to its ... This 250-word extract was created in the absence of an abstract.
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