Reservoir Characteristic Study Of The Chang 9 Formation In Huaqing Area,Ordos Basin

Huaqing area in the tectonic position is the southwest of Yishan slope of Ordos Basin,it is in the west of Tianhuan depression and in the south of Weibei uplift. Chang 9 reservoir group currently has a good exploration potential evaluation, but the area is controlled by sedimentay environment and diagenesis,so the effect of exploration and development is not ideal. Therefore it is necessary to carry out the sedimentary microfacies, reservoir petrology and diagenesis research on accout of Chang 9 formation in Huaqing area, conforming the reservoir characteristics and favorable reservoir distribution and providing the geological basis for the exploration and development in the furture.Taking advantage of well logging, drilling and core observation,cast thin section and scanning electron microscope, X ray diffraction and constant rate mercury injection, nuclear magnetic resonance and other methods, this paper,combing with the regional geological data of the studying area,systematically studied the characteristics of Chang 9 reservoir in Huaqing area.The results show that Chang 9 oil-bearing formation in Huaqing area is mainly delta system and lake system. The delta system is a kind of shallow lake sedimentary, and the delta system main subfacies are delta front deposition which is further divided into underwater distributary channel,interdistributary bay and mouth bar microfacies.Chang 91 sandstone and Chang 92 sandstone is NE-SW banded distribution in plane,and the thickness and the plane distribution scale of Chang 91 sandstone are smaller than that of Chang 92. Chang 91 is mainly arkose and lithic feldspar standstone and Chang 92 is mainly arkose, and interstitial material content is extremely uneven and it is mainly cement. Sandstone developed residual intergranular pore,dissolution intergranular pore,dissolution intragranular pore and laumontite solution pore,and it had good connectivity,otherwise it developed a small number of frature pore and cast film pore.The pore structure is mainly small pore-micro throat and meso pore-micro throat.Reservoir has strong inner layer,inter layer and areal heterogeneity.Reservoir underwent compaction and pressolution, cementation and dissolution and so on.Among them,destructive diagenesis by compaction, carbonate cementation,felsic cementation and clay mineral cementation and constructive diagenesis by chlorite cementation,laumontite and feldspar dissolutio,Chang 9 sandston has already been in stage A of the middle diagenetic stage.It is divided five kinds of diagenetic facies,which are chlorite membrane-intergranular pore+laumonite dissolution phase, chlorite membrane-intergranular pore+feldspar dissolution+laumonite cementation phase, ferrocalcite cement+chlorite membrane-intergranular pore+feldspar dissolution phase,siliceous cement+ferrocalcite cement+chlorite membrane-intergranular pore+feldspar dissolution phase and ferrocalcite cement+ hydromica cement+siliceous cement phase,in which the first three are favorable diagenetic facies and the latter two are unfavorable diagenetic facies.Through the above research,the reservoir in the study area is divided into 5 classes,classⅠand class Ⅱ reservoir distributed in the middle of underwater distributary channel,class Ⅲ is mainly distributed in the channel flank,class Ⅳdistributed in the channel side. classⅠ~Ⅲ are favorable reservoir,and class Ⅱ and class Ⅲ are the main reservoir in thin study area, and local area developed classⅠreservoir.