Geometry Determination of Channel - Fill Deposit Induced by Turbidity Current: A Study from an Outcrop Analogue

Geometry Determination of Channel-fill Deposit Induced by Turbidity Current: A Study from an Outcrop Analogue

Adlirrahman Aufar1, Octria Adi Prasojo2*, Reza Syahputra2, Twin H. W. Kristyanto2, Felix M.H. Sihombing3

1,2Geology Study Program., FMIPA, Universitas Indonesia,

Kampus UI Depok, Depok 16424, Indonesia

3Freelance geologist

*octria.adi@sci.ui.ac.id

ABSTRACT

Channel system produced by turbidity current has been proved as one of the most prominent hydrocarbon reservoir. Geoscientists find many challenges to characterize and to predict the geometry of the turbiditic deposit because of their complexities, diversities, and outcrop scarcities. Thus the objective of this research is to understand the geometrical characteristic of turbiditic channel and how it is generated by studying its outcrop as an analogue for subsurface hydrocarbon reservoir. This study discusses geometry determination and paleogeographical environment from the outcrop. From the field observation, we found that the turbidite facies is encased in muddy deposit of other associated facies. The turbidite facies composed of interbedded coarse-grained sandstones and very coarse-grained in the lower part with planar and cross-bedding sedimentary structure. The base of this facies is sharp or locally show erosional surface with burrows commonly observed in the middle or upper part of the facies. The dimension of this package is 360 cm thick with overall fining-upward pattern in the uppermost 100 cm. Overall geometry of the outcrop represents a lens of channel-fill deposit induced by turbidity current. Shale layer wrapping this facies indicates the clean sandstone turbiditic channel-fill deposited on shaly seafloor. Further study on petrophysical characteristics of the outcrop will make this outcrop as legitimate reference to characterize subsurface turbiditic reservoir.

INTRODUCTION

Sediment waves with a turbidity current origin commonly associated with particle-laden underflows that occur in lake and ocean bottoms [1,2,3]. Turbidity currents are submarine density flows which driven excess of a sediment loaded current over its ambient fluid, which in the case of turbidity current, the sediment is kept in suspension by turbulent flows [4].

The turbidity currents also have heterogeneities characterization where usually conducted with outcrop observation or subsurface data. Yet this kind of approach cannot simulate exactly the physical process that produce the channel fills induced by turbidity currents. [3]. Moreover the overall geometry of this kind of outcrop have not yet clearly been documented, a part from for a few cases in big outcrop exposures [5,6].