DEPOSITIONALAND DIAGENETIC CHARACTERS OF SEDIMENT IN THE “D” PROSPECT EAST JAVA, INDONESIA: INTEGRATION OF ROCK PROPERTIES AND ISOTOPES AS AN EXPLORATION TOOL
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Abstract
The two wells in “D” Field, D-2 and D-3, from offshore Indonesia, have distinct depositional and isotopic signatures, implying they experienced distinct diagenetic histories. The neutron-density log is used to distinguish specific features that occur in the carbonate interval, with higher porosity generally tied to vuggy fractured zone. Core plug measurements show higher values in well D-3 compared to well D-2. Measurements of stable C-O isotopes from core in both wells are used to define the diagenetic history and the constrasts between the two wells. This differentiation can affect the economic value of the carbonates in the two wells. Carbonates in the D-2 and D-3 wells have distinct isotope signatures, implying they have experienced distinct diagenetic histories and for a classic “T”trend made up of a burial trend and a meteoric mixing trend. Most of the carbonate sampled in the D-2 well shows a typical burial re-equilibration response, related to carbonate dissolution and re-precipitation from pore fluids with increasing temperatures associated with increasing burial depths (the upper arm of the “T”). There are another group of samples in the D-2 well that show a second trend of increasingly negative carbon values that constitute the subvertical arm of the “T”. These “second trend” samples are typically from zones of leaching, fracturing and dissolution. In contrast, there is no burial trend seen in the isotope results of the D-3 well. Carbonates in the D-3 well are grainier and more heavily overprinted by the effects of calcite recrystallisation and leaching. The isotope results suggest the grainier sediment interval sampled in the D-3 well acted as an aquifer that carried deeply-circulating meteoric waters, which in turn drove a more pervasive diagenetic overprint in this well compared to the muddier section in D-2. It may be that carbonates in the D-3 well were better connected to an aquifer source, tied to the exposure surface induced by the Miocene uplift and the resulting unconformity.
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Copyright © 2008 Department of Geology, Faculty of Science, Chulalongkorn University. Parts of an article can be photocopied or reproduced without prior written permission from the author(s), but due acknowledgments should be stated or cited accordingly.
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