Deepwater Source Models and Their Integration into 3D Petroleum Systems Modelling: A Case Study from Deepwater NW Sabah, Malaysia

Peter Abolins¹ and Azlina Anuar^2
1PETRONAS Carigali Sdn Bhd, Kuala Lumpur, Malaysia
²PETRONAS Group Research, Selangor Darul Ehsan, Malaysia

Active exploration in the deepwater offshore northwest Borneo has raised many questions regarding the presence and distribution of source rocks in these settings. We are often unable to provide definitive answers to such fundamental questions as the source rocks are not penetrated. As the results of petroleum systems modelling are very sensitive to source rock quality and distribution, the development and incorporation of a robust source model are critical in 3D modelling. Analogue studies often provide useful insights into likely source rock facies. This paper discusses the fieldwork results of onshore analogue studies and illustrates how these analogues were incorporated into the 3D model.

In deepwater NW Sabah, possible candidates for source rock facies include bathyal pelagic shales, slumps and debris flows, organic rich turbiditic sands, and levee and overbank shales. Of these, the analogue studies indicate that slumps and debris flows were observed to be the organically-richest facies, with the organic matter being predominantly of terrigenous origin. Recent work by operating companies in offshore Sabah has revealed that turbiditic sands can also contain significant quantities of terrigenous organic material.

To test this conceptual model for source rock deposition in deepwater NW Sabah, a petroleum systems modelling study was undertaken. The selected pilot area incorporated both explored (for calibration) and frontier areas of offshore NW Sabah. The objectives of the study were (1) to demonstrate that the conceptual model could reproduce the known hydrocarbon distribution in the pilot area, and (2) to assess hydrocarbon charge likelihood in unexplored areas selected for basin modelling. The tools and concepts used included a robust conceptual source rock depositional model and personalised kerogen kinetics. Much time was spent incorporating our new understandings of NW Sabah source rock distribution into the basin model to ensure that the constructed basin model accurately reflects the underlying geological model. This included incorporating expected Total Organic Carbon content, kerogen types and kinetics for each main source rock facies into litho-facies maps. The facies maps were then assigned geochemical properties typical of each facies as defined by the source rock conceptual model described above.

The deepwater pilot study area was subsequently divided into three regions based upon the anticipated available charge: oil charged, gas charged, and mixed oil and gas charged regions. There were occasional situations where observed oil and gas distributions do not agree with that predicted; there is a likelihood that they are caused by top seal issues and/or a manifestation of phase behaviour affects. To date, the results of recent exploration wells have agreed well with the 3D model predictions.

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands

 

AAPG Search and Discover Article #90066©2007 AAPG Hedberg Conference, The Hague, The Netherlands