The Study On Characteristics Of The Ordovician Carbonate Reservoirs In YuQi Area

The existing exploration results show that the main strata is Ordovician carbonate, and have many types of reservoirs and the formation mechanism of reservoirs is complicate, heterogeneity of reservoirs developed ,which add the difficulties to the next exploration and development in YuQi area.This paper study on the space of reservoirs and the types of reservoirs on the Ordovician carbonate by the data of core and thin section and logging. The results show that reservoirs space can be divided into the dissolution of cavity, karst caves and fracture etc. The type of Ordovician carbonate reservoirs can be divided into the reservoir of karst caves,reservoir of karst fracture-cave system, reservoirs of dissolution cavern and fractured reservoir by the space of the reservoirs and their association. Connected with well logging information and logging data,this paper comprehensively analysis the Ordovician Reservoirs of all the wells in this region, it is suggested that the dominating reservoirs are reservoirs of karst caves and reservoirs of karst fracture-cave system, besides, the significance of the solution cavern reservoirs less than the two above.This paper study on the diagenesis of Ordovician carbonate. The results show that the main diagenesis of the region contain cementation, silicification, pressure solution, dolomitization, dissolution, karstification and cataclasis. This paper mainly focuses on the Karstification. The development and distribution of Ordovician carbonate reservoirs is primary controled by the Early Hercynian karstification and Late Hercynian karstification in Yuqi area. Where covered by the Carboniferous strata in the southern area of Yuqi is mainly dominated by Early Hercynian karstification, and wherea covered by the Triassic strata in the northern area of Yuqi is dominated by Late Hercynian karstification. The Early Hercynian karstification model follows "the karstification model of normal atmospheric water level ", under the control of Early Hercynian karstification,There exists three karst cycles and develop three sets of karst cave reservoirs under the unconformity surface, in which the most developed set of cave is the second karst cave. The main reservoirs are the reservoirs of karst, the development of which is controled by the Early Hercynian karstification.Researching on the combine characteristics of Ordovician carbonate reservoirs and seal ,the results suggest that the regional seal is C1b2-3+C1kl1,the directly capping is the Bachu group glutenite segment of Carboniferous(C1b1),lower mudstone segment (C1b2), Donghetang group(D3d), Upper Ordovician (O3q), Triassic strata (T). Combine characteristics of reservoirs and seal in different regions is variable, the best is in the south-east where the Upper Ordovician is conserved; in the south area along YQ3-YQ4-YQ7 where C1b2 directly covering on the top of the Lower Ordovician, has the best combine characteristics of reservoirs and seal; in the west of Yuqi along YQ2-YQ5-YQ9 and in the east along YQ1-YQ6 , the seal indirectly covers on the Lower-Middle Ordovician, is relatively poor; and in the north,along LN13-LX4 and north of LX4 , the combine characteristics of reservoirs and seal is poor.By the study of the formation mechanism or development and distribution or controlling factors or evaluation of the reservoirs, it is shows that southwest and southeast where the seal directly covered is the favorable area, and the seal indirectly covered is the beneficial area, the northern region is the third area, while where the upper Ordovician strata conserved is poor.