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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


24th Annual Convention Proceedings (Volume 2), 1995
Pages 45-59

Determination of Previous HitPermeabilityNext Hit in Previous HitSandstoneNext Hit Reservoirs Affected by Diagenetic Kaolinite, Cinta Field, Southeast Sumatra

Paul C. Tonkin

Abstract

The Cinta Field lies 95 kilometers northwest of Jakarta within the Sunda Basin area. Late Oligocene sandstones of the Talang Akar Formation provide an excellent reservoir in a structure defined by arching over a rotated fault block high that is the northern edge of a major half graben. The Cinta Field structure separates the Sunda Basin to the north Previous HitfromNext Hit the Kitty-Nora Sub-Basin to the south. The field has produced 206 million barrels of oil (32.8×106 m3) Previous HitfromNext Hit fluvio-deltaic clastics of the Talang Akar Formation and overlying Baturaja Formation reefal carbonates.

Studies on cores cut Previous HitfromNext Hit recently drilled wells show that the reservoir sandstones frequently contain large amounts of pore-filling clays, largely in the form of kaolinite. This kaolinite is believed to have resulted Previous HitfromNext Hit the breakdown of potassium feldspars formerly within poorly-sorted volcanic detritus. Previous HitPermeabilityNext Hit within the reservoirs can be drastically reduced by the presence of diagenetic kaolinite, the amount of which depends on the extent of the alteration of the feldspars as well as the original feldspar content.

Previous HitPermeabilityNext Hit can be approximately determined Previous HitfromNext Hit wireline log information. The critical factors determining Previous HitpermeabilityNext Hit are porosity, which is dependent on grain size and sorting, and the amount of kaolinite present. In Cinta, the gamma ray log responds to kaolinite, probably due to the presence of small amounts of thorium associated with this clay. A mathematical fit of data Previous HitfromNext Hit the Cinta B-6 and F-11 cores, shows a good correlation between gamma ray response and the density-derived porosity with the measured Previous HitpermeabilityNext Hit. A series of hyperbolae give a best fit of data for determining Previous HitpermeabilityNext Hit Previous HitfromNext Hit wireline logs in uncored wells.

Whilst the method is at best an approximation, it is specific to Talang Akar sandstones within the field and can be used to assess reservoir quality in unperforated pay intervals and to predict low and high Previous HitpermeabilityNext Hit reservoir sections. Some high Previous HitpermeabilityNext Hit zones lack clay cements, and these are usually friable and prone to sanding in a producing well.


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