Abstract

This paper discusses establishing a reservoir geology model for a part of the Rantau Field utilizing two methods. The first method based on log data only, while the second model utilizes a combination of 3D Seismic and log data. Geostatistic techniques were used to determine how seismic attributes correlate with reservoir properties and the best way to interpolate reservoir properties.

There are 60 wells included in this study, only 8 wells have porosity data available that control points and 3 wells have been producing oil more than 30 years.

The results of this study proved that fault patterns from the seismic interpretation were consistent to the faults established using log data. Netsand thickness and effective porosity is getting better from the NE to the SW.

The techniques presented in this paper demonstrates that combining well log data and seismic data can be used to produce more accurate reservoir geology maps.

Introduction

The purpose is to integrated 3D seismic and well data to determine reservoir model.

Well log data provide detailed information about vertical resolution of many reservoir properties but only in region relatively close to the well bore. 3D seismic data with good lateral resolution can be helpful to describe the reservoir away from the well bore.

Integrated of 3D seismic with well log data can significantly improve the special interpolation of petrophysical properties and reservoir geometry.

The flowchart of study is illustrated in fig 1. Interactive workstation has been used for all the study. (Integral Plus)

Field History

Rantau field were found more than 50 years ago, 550 oil wells have been drilled to develop the field until now. Long process of that production is expresioned with condition of reservoir deplesion.

Discovery of oil as optimum be done as promer and secunder at zone 600. As extensification SECREC at zone 600 and other reservoir potention determining, 3D seismic be printed, processed and be interpretated in 1994/1995 Wide of area of 3D seismic survey is 40 km square. Covering of all Rantau structure with design distance between two lines 200 m, bin size 20x20 m at objective 700 meters.

Block-C area is 6 km square, 60 wells in it with old and complete logs. Only 8 wells have porosity log (Neutron, Density Log).

Geological and Stratigraphical Setting
Geological Setting.

The Rantau block occupies the central part of the tertiary North Sumatra basin and is bounded to the East by the Malaka Platform, the Asahan arch to the South and the Barisan mountains in the North. The Asahan arch is believed to be the boundary delimiting the North of the Central Sumatra basin area.

The North Sumatra Basin developed during early Tertiary times and divided into several sub-basins by younger tectonic events, namely the Tamiang, Medan, Paseh and Pematang Siantar sub-basins. Two major episodes of tectonism affected the basin. The first took place during the early Tertiary and involved the breakup of the pretertiary basement into fault blocks which control the early tertiary depositional strike-slip movements along the Sumatra trend. The main characteristics of the Rantau Block are the older (NE-SW trending) and the younger (NW-SE trending) structural. The most prominent structure in the area trend and the block faulting in the basement which greatly affected the overlying sedimentary structure. The surface expression of these faults often appears as gentle low-angle thrusts and the present structural configuration produced by later Plio-Pleistocene folding. The tectonic elements of the North Sumatra basin illustrated in Fig. 2.

Stratigraphy. The stratigraphic framework of the North Sumatra basin starts with an early tertiary sedimentary sequence composed mainly of micacoeus quartz sandstone with some transgressive carbonate units, overlying the pretertiary basement.

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