Abstract:

Ba-Mai area stands for the Bachu uplift and Mageti slope in SW Tarim basin, it has a paleo-tectonic and paleo-geographic background of platform margin-slope, which implies a typical reef-bank environment characteristics. There are three layers of limestone developed in the XBZ 3D seismic working area, C₁b biological clastic limestone, standard limestone and C₂x limestone, in which a special seismic response carbonate was found, the main response characteristics are thickness and frequency increasing with an extra peak event. It can be indicated that the low velocity abnormal body was caused by a near EW platform margin barrier reef through different thickness, subface flatten, seismic attribute and forward and inversion methods, combined with analysis of field outcrops, core, microscopic observation, logging and sedimentary facies. The reef extends more than 25 km in EW, the maximum thickness of reef core area of C₂x limestone is 62 m, outside thickness is 50 m. Platform margin slope trends to south, which has a 1-2 km horizontal width. Biological clastic bank behind the reef trends to north, the horizontal width is 3-6 km. Blocked by Selibuya fault, reefs traps can be formed, reefs area is about 42 km² and about 45 m thick.

Key words: low velocity anomalous body, carbonate, Xiaohaizi Formation, Carboniferous, Ba-Mai area (Bachu-Mageti slope), Tarim basin