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Deep Exploration Challenges in a High Pressure Ultra-High Temperature (HPXHT) Environment: The Central Malay Basin, Offshore Peninsular Malaysia

Benan, Cheikh
Exploration, Total E&P Malaysia, Kuala Lumpur, Malaysia.

The Central Malay Basin (CMB) is characterized by: (1) a thick sedimentary pile with more than 10 km for Upper Oligocene to present-day sediments, (2) a shallow top of overpressure at less than 1 km in depth in some locations, (3) an anomalously high temperature gradient 57degC/km, and; (4) the presence of unpredictable concentrations of CO2 that affects the prospect volumetric assessments and any future development management and planning.

Seismic imaging of the CMB thick sedimentary series is challenging when aiming at deep HPXHT targets because of the presence of shallow hydrocarbon accumulations and even shallower gas cloud blurring. This creates significant shallow lateral velocity variations resulting in signal attenuation and imaging geometry problems in deep seismic section. Therefore, dedicated seismic velocity picking as well as the use of recent multiple attenuation processing sequences and PSDM processing are required. This is the sine qua non condition for defining reliably any prospect geometry and to image deep sedimentary reservoir features.

In the CMB, the series are strongly over-pressured. Shale compaction disequilibrium has been the main mechanism in the overpressure generation. At a regional scale, studies indicate a quick and strong pressure ramp up due to a high sedimentation rate, low sandstone/shale ratio and restriction in drainage conditions. On the other hand, an increase in the sandstone/shale ratio towards the basin hinges produced a lower and deeper pressure ramp up. The CMB high temperature gradient affects the reservoir quality risk prediction as well as the petroleum system generation and timing. It is also thought to be the main driver in the generation of CO2.

The combination of high pressure and ultra-high temperature challenges are not only on the petroleum system and the traps integrity but also on the definition of the mud weight window for "drillability" (pore pressure predictions), the well design as well as operations and data acquisition (logging and testing). One has to keep in mind that the HPXHT exploration requires integrated methodologies for pushing the well specification envelopes and to bring leading edge technology and while keeping a safe environment.


AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012