Publications

Successful Geological Strategy for Setting Intermediate Casing Prior Approaching Kujung Carbonate in Jambaran Field, Cepu Block

Proceedings Title : Proceedings, Indonesian Petroleum Association, Digital Technical Conference, 14-17 September 2020

Jambaran Field was discovered in 2001 by J-1ST1 exploration well. The discovery well encountered steep-flanked carbonate build-up structure (Kujung Fm) that contain thick gas column and thin oil rim. To date six more wells have been drilled to unravel the geometry of the carbonate build up reservoir type. The carbonate build up which is up to 10 km length and 1 km width was deposited during Oligo-Early Miocene and sealed cap by very thick Tuban shale. This stratigraphic configuration has caused several drilling risks. First, there is a huge drop in pore pressure value between Tuban Shale and Kujung Carbonate; of up to 12.6 ppg in Tuban Shale and 8.1-11 ppg in Kujung Carbonate. Second, shale instability commonly happened during drilling Tuban shale. Third, total loss circulation, which can lead to H2S gas kick, potentially happened once penetrating Kujung Carbonate. To reduce those drilling risks, the casing ought to cover as much as Tuban Shale and as close as possible to Kujung Carbonate. During the exploration wells drilling, conventional methods such as; cutting observation, wetness-balance gas ratio, calcimetry, and mud losses have been applied to hunt the casing point as close as possible to Kujung Carbonate. Those conventional methods were successful in several well but also failed in the others. There are many other sophisticated tools developed by Service Company to serve the purpose of set casing, such as resistivity at bit. However, in our ongoing development wells drilling campaign, we utilized the combination of those conventional methods successfully to set 9-5/8” casing point as close as possible without entering Kujung Carbonate.

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