Facies Modeling of Fluvial Depositional Environment: Case Study from Early - Middle Miocene Deposit of Barabai Member, Barito Basin

Pradana, Aulia¹; Setiawan, Muchlis²
¹Geology, Bandung Insitute of Technology, Bandung, Indonesia.
²Geology, Padjadjaran University, Bandung, Indonesia.

Reservoir from fluvial deposit play important role in oil and gas industry. The important problem about this reservoir type is how to recognize it in subsurface analysis and how to make its 3D quantitative model. That problem occurred because of fluvial deposit is a relatively complex reservoir which has large heterogeneity in reservoir quality. The heterogeneity problem is caused partly by differences in facies distribution of each type of channel.

3D facies modeling take an example case from Field ETTN, which is one of the oil-producing fields in the Barito Basin. One of the major reservoirs in this field is sandstone R intervals, which is included in the Early - Middle Miocene Barabai Member. R intervals are divided into three intervals called R1, R2, and R3 based on shale that separate them. Facies analysis and modeling starting with the conventional core analysis was doing to get lithofacies association. All the results of the analysis are associated with the pattern of gamma-ray logs to get a log model that can be used to correlate facies associations through all well. The next stage is to perform 3D modeling for structural and facies. To get more realistic model the procedure of facies model divided into several steps, first figured out the width versus thickness of each facies based on the channel type, and input the detailed facies model using stochastic models. Truncated Gaussian simulation was used to describe transition zone of each facies. The final results of the reservoir characterization are structure maps, thickness maps, and 3D facies models.

This study concluded that based on Schum (1981) channel classification, R1 and R3 interval interpreted as bedload channel and R2 as a mixed load channel. Based on integration of core and well log data this fluvial channel is divided into five facies associations: channels axis, bar head unit bar, channel margin, floodplain, and crevasse. Channel margin facies association developed at the southern part of the study area which gradually changes to channel axis to the northern part of the study area. Bar head unit bar develop at central area overlying the channel axis facies association. Flood plain developed at the top of each interval and contains deposit of crevasse. Channel axis, channel margin, crevasse and unit bar deposit act as reservoir in this field. By knowing the properties and distribution of each facies in this field, the hydrocarbon development scenario can be made more accurate.

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