Study On Application Of Magnetotelluric In Oil And Gas Resources Survey Of Nima Basin

The Bangong stuture zone between the Lhasa and Qiangtang terranes has complex mineralization.A series of super large-large metal deposition have been identified in this area.And the Lunpola basin located in this stuture zone is the first oil-bearing basin that industrial oil flow is discovered.Thus,the Nima basin,one of the Lunpola basin groups,which has similar sedimentary characteristics with the Lunpola basin,received increasing attention from the academic community.In order to find out the oilproducing potential of Nima basin,various geological and geophysical prospecting have also gradually been carried out in Nima basin,but the exploration level is still low presently.To identify the oil-generating potential of the Nima basin,oil generating condition and migration condition should be concerned.Oil generating condition could be judged by field geological investigation on development of source rock.And the existence of migration conditions requires study on subsurface geologic structure by using geophysical methods to find out whether there is a suitable combination of reservoir and cover.Magneto telluric sounding cost little,can explore very deep and identify strata and traps effectively,which could satisfy needs above very well.Thus,magneto telluric sounding would be chosen in exploration in the study area.In this thesis,the measured data of four magneto telluric survey lines emplaced in the southern depression of Nima Basin are processed and inverted.The inversion results were explained on the basis of field geological investigation data,core data,and previous study.The stratigraphic distribution and fracture development in the southern depression were discovered.Based on this,this thesis infers the tectonic movement period and tectonic movement mode of the basin,combined with geological data and previous study.Here are the results:(1)A consensus on the division of tectonic units is that the Nima Basin can be divided into three primary structural units--the Southern Depression,the Northern Depression and the Central Uplift,which is contrary to the result of this thesis.Through the inversion and interpretation of the Magneto telluric data,it is found that this structure is a klippe caused by thrust and denudation rather than a Jurassic uplift structure.(2)According to the inferred result,the south and north borders are defined.Referring to previous research in sedimentology,chronology and paleolakes,the evolution process of Nima basin was inferred as followed: the stratigraphic sequence was deposited till the Eocene.After that,the study area was suffered from a strong compressive,as a result,the Triassic and overlying strata in the northern part of the study area were overthrusted to the central uplift area of the Nima Basin.And then,because of the denudation,the Jurassic strata were exposed and the deposition resumed in the Quaternary period.(3)The oil and gas prospects in the this area was indicated according to the structure feature,sedimentary characteristics and the petroleum geological conditions.The southern depression of the Nima basin has a thick Niubao formation deposit,a good Quaternary caprock.It has a good oilproducing potential and deserves further investigation,although it has experienced many multi-stage movements.