Abstract:

Baise Basin,located in the western part of Guangxi Province,is a narrow Tertiary sedimentary basin striking NW and occupying an area of 830km².This basin is the biggest one among the five Tertiary basins in Guangxi Province and has a history over 20 years in petroleum prospecting.The Tertiary sediments in this basin are of 2,700-3,400m thick.Among other things,the late Eocene Nadu Formation (E₃n) and the Oligocene Baigang Formation (E₃b) are both source rocks and reservoir rocks.In addition,lime-stones of the middle Triassic Lanmu Formation (T₂l),which constitutes the basement of the basin,also serve as reservoir rocks.Source rocks of Nadu For-mation is as thick as 700m.Organic matters in the rocks are primarily sapropel or intermediate types.Geothermal gradient observed in this basin is 3.4℃/100m.The thresholds of oil generation are respectively 1,200m (64℃) and 1,400m(71℃).The basin could be divided into three depressions and two uplifts,i.e.Tiandong,Baise and Tianyang depressions and Nabai and Sitang uplifts.Tiandong is the biggest depression among the three and has been highly ex-plorated.Till now,8 oil and gas pools discovered are all distributed along this depression and the neibouring Nabai uplift.The step-faulted zone in north of the depression is oil and gas enrich zone.Oil pools in this basin are in various small traps,such as anticlinal trap,fault block trap,lithological trap or even more complicated trap.The buried depth is 22.6-1,935m.Crude oil is low-sulphur paraffin-base,and is charac-terized almost by primary or oxidized type.Some oil traps are capped with gas.The formation waters are NaHCO₃ type.