Abstract

The existing geological and well data show there are plentiful karsting carbonate in Ordovician formation in LN Depression of Tarim Basin, but the old seismic data was not adequate for karst mapping because of the low resolution. In order to investigate the possibility of buried hill reservoir in the area, a highresolution 3D survey in Sangtamu Block was carried out. The purpose was to map the detailed features of the karsting and provide ideal location for drilling.

Both acquisition and processing were emphasized on high temporal resolution based on high S/N ratio.

The acquisition parameters were chosen to adopt single well, small charge, 1 ms sampling, 20×20 m cell size and 24 fold of coverage. High resolution full 3D RAP processing was performed, and the final section displayed high quality with dominate frequency of 48 Hz, laying a good foundation for karsting interpretation.

Combined with the available geological and petrophysical data, the structure interpretation and reservoir characterization with palaeotectonics and palaeogeography study were carried out for better understanding of karsting development. By analyzing the karsting features and the surrounding environment, a number of drilling locations were selected and all successful. Among them, well LG9 and LG15 gave the initial production of 228 ton and 608 ton a day respectively. The integrated 3D project added 80 million tons of reserves to the oilfield.

Introduction

The carbonate is ideal reservoir rock because of its high porosity. Statistics show more than half of the proven oil reserves in the world are in carbonate reservoir. The existing geological and well data show there are plentiful karsting carbonate in Ordovician formation in LN Depression of Tarim Basin, the surrounding rock has good generation condition, while the upper rock can be good cap, but the old seismic data is not adequate for karst mapping because of the low resolution. In order to investigate the possibility of buried hill reservoir in the area, a high-resolution 3D survey in Sangtamu Block was carried out. The purpose is to map the detailed features of karsting and provide ideal location for drilling.

The Sangtamu 3D, with the total size of 457 km2, was designed on the central location of LN Karsting High. The acquisition was emphasized on high temporal resolution with high S/N ratio.

After analyzing the experiment data, the acquisition parameters were chosen to adopt 6 line by 24 shot layout, single well of 6 m, small charge of 2–3kg, 1 ms sampling, 20×20 m cell size and 24 fold of coverage. The on-site processing section shown good quality with the dominant frequency of 40 Hz. The high-resolution full 3D RAP processin

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