The Overpressure Mechanism Identification in Unstable Shale Environment

Abstract

The shale stability becomes the main concern of any drilling campaign all over the world. Most of the drilling problems initially come from shale instability in subsurface. Based on some papers the shale instability related to mineralogy (diagenetic process), fractured or faulted shale, over-pressured shale, angle of incident and direction of the well, mud management, unwise drilling practice, etc. We will do some general approachments to highlight the overpressure mechanism that govern the unstable shale lithology interval. It is important to identify the overpressure mechanisms that involved originally in the shale environment in order to see the relation of this geology phenomenon to any of drilling campaign. This paper will summarize two different study cases that were known to have unstable shale in overpressure environment. The first case study will be from Middle East and the second case study will be from North East Java basin in Indonesia. Identifying the mechanism will help to understand the relation between geology and the drilling phenomena in real time and hopefully this result will be useful for drilling adjustment in future time. There are two major mechanisms in overpressure, disequilibrium compaction (loading) and unloading (related to shale diagenetic and hydrocarbon generation), that dominantly play in some overpressure environments. We also will compare and identify the drilling phenomena in order to relate to the resulted mechanism and understand about the unstable shale lithology in these two case studies. These findings will help service provider and client to understand details about the unstable shale and relation between the overpressure mechanism and the drilling phenomena in real time. Hopefully, this paper can be used as a reference to anticipate any drilling problem in unstable shale in future time.

AAPG Datapages/Search and Discovery Article #90336 ©2018 AAPG Asia Pacific Region, The 4th AAPG/EAGE/MGS Myanmar Oil and Gas Conference, Myanmar: A Global Oil and Gas Hotspot: Unleashing the Petroleum Systems Potential, Yangon, Myanmar, November 13-15, 2018