A Study On The Structural Characters Of The Lun Po La Basin In Tibet

The oil and gas indication distributes widely on the north and south belt of the Lunpola basin, but there is only one well z-1 getting the industry production of normal oil. It is the vague knowledge about the middle -deep structural character that causes uncertainty of structural trap's distribution. For solving the problem above, this paper takes advantage of 2D seismic migrated time data mainly, contrasting 2D seismic stacked time data and 3D seismic data simultaneously, to carry out the seismic interpretation of structure in the Lun po la basin. And on such basis, the paper analyzes the structural features of the Lun po la basin in three-dimension by structural mapping. Then, look for the structure traps in the middle-deep depth. At last, make sure the optimal trap and suggest the poisons of the exploration wells.The present Lun po la basin has dumbbell-shape with "separated belts in north-south trends and separated blocks in east-west trends" tectonic framework. The north thrust-nappe belt shows high angle thrust faulting. On the hangingwall, it exposes the Niu bao formation or basement; Under the Hong Fr3 fault is the autothonous system which exhibits fault block or fault anticline. Their high points' depth is generally over 1500m. All of them belong to the middle-deep structures and are the potential trap structures; the south thrust-uplift zone has thin formation sediments which have been eroding seriously. The football of thrust fault remains the normal fault system. So the oil preservation in the south thrust-uplift zone is not good. In the middle of the basin is central depression zone. It can be divided into five secondary structural unites by Jiang Fn10, jiang Fn5 and Hong Fr4 faults which include Jiang ri a cuo sag, Jiang jia cuo sag, Pa cuo sag, Hong xing liang-Pa long yao ma fault-fold belt and Niu bao flexture zone.By using the seismic profile and structural map, the research has found 29 trap structures altogether, according to the reflection layer,110 trap layers in the basin. The traps on the bottom of the third section and the upper second section of Niu bao formation are striking. The high points of them are deeper than 1500m commonly. The paper chooses 9 typical trap structures which include Jiang No.3,4 trap structures in the south of Jiang ri a cuo sag; Jiang No.2,4 and 6 trap structures in the north of the Jiang jia cuo sag. The north of the Jiang jia cuo sag is Lun No.1,2 trap structures; Luo No.1, 2 trap structures located the north of Pa cuo sag, on the other side, it is Chang No.1 trap structure. Then combining the source rock, reservoir rock, cap rock, trap condition and oil play process in the basin the paper chose the bottom of the third section and the upper second section within Niu bao formation in Luo No.1 trap structure and the upper second section within Niu bao formation in Jiang No.6 trap structure as the preferred traps. The former two reflection layer traps have the same closure:140m, separated areal closure:8.25km2 and 3.75km2. The later trap has closure:240m, areal closure: 2km2. So we suggest two exploration wells on the high points of the traps.