Research On Sequence、sedimentary Facies 、developmental And Distributive Rules Of Reservoir In The Yijianfang Formation In The West Of Tahe Oilfield

The carbonatite of the Yijianfang Formation in Ordovician in the west of Tahe Oilfield is regarded as a research object in this paper. Basing on the research achievements of predecessors, using combined theories of multi-discipline such as sedimentology sequence stratigraphy、reservoir sedimentology, as well as using the comprehensive analytical methods of core observation and description、thin section identifition under microscope、drilling 、mud logging、logging and so on, the research of sequence、sedimentary facies、reservoir in the Yijianfang Formation in Ordovician in the study area are carried out. By integrated dissecting of reservoir in relevant wells in the study area, as well as discussing the relationship between reservoir development 、 distribution and strata sequence 、 sedimentary facies, the rule of reservoir development 、 distribution and influencing factors are summarized in the study area.. principal results are as follows:(1) The third-order and forth-order(high frequency) sequence screenwork of the Yijianfang Formation in Ordovician in the study area is established. The Yijianfang Formation in the study area could be divided to one independent third-order sequence,five forth-order sequences further. Form the bottom to the top, the forth-order sequence is respectively the sequence ofⅠ、Ⅱ、Ⅲ、Ⅳ、Ⅴ.The third-order sequence is made up of transgressive system tract and highstand systems tract. Two forth-order sequences are included in the transgressive system tract and three forth-order sequences are included in the highstand system tract. With fine chronotaxy, the third-order sequence and the forth-order sequence could be correlated across the whole area.(2) Carrying the shoal explanation in the study area out effectively, as well as taking the forth-order sequence as a unit, the sedimentary facies and shoal distribution in the Yijianfang Formation in the study area are depicted, thus the isochronally and dynamically space-time distribution and evolution of sedimentary facies as well as the shoal body is revealed. Through the revealing of fine depiction of the shoal bodywithin the forth-order sequence unit, there doesn’t develop shoal body at the late of the transgressive system tract, namely the period of the Ⅱ forth-order sequence, but only small-scale shoal patch locally. These intraplatform shoals are growing gradually at the early of the highstand systems tract, namely the period of the Ⅲ forth-order sequence, but its scale are small still. When it comes to the middle or the late of the highstand system tract, the shoal body is at its advantage of development with the Ⅳforth-order sequence being specific and the development of the intraplatform shoals in the area is at its heyday, mainly forming the two giant shoal bodies in the north and south. On the arrival of the Ⅴ forth-order sequence, the intraplatform shoals start to decline, with the number increasing and scale decreasing.(3) Analysis reveals the development situation of the reservoir. The dissolved pore reservoir、the karst-fractured-cavity reservoir、the cave reservoir as well as the fracture reservoir are developed in Yijianfang Formation in the study area in the middle of Ordovician. It reveals that karst-fractured-cavity reservoir is most developed. The study of this areas, ordovician formation mechanism of accumulation space shows that the formation mechanism of accumulation space includes atmospheric water,s denudation on syndiagenetic stage 、 atmospheric water, s denudation in the middle Caledonian、atmospheric water,s denudation in the late Caledonian-early Hercynian、hydrothermal activity in the late Hercynian and fracture diagenesis.The dissolved pore reservoir is controlled by the role of atmospheric water,s denudation on syndiagenetic stage; The karst-fractured-cavity reservoir is mainly result from the atmospheric water’s denudation in the late Caledonian-early Hercynian and the fracture reservoir are is controlled by racture diagenesis.(4) The distribution of reservoir has been studied. Through analysis, the development of the reservoir is strongly of the characteristics of distributing on the top. Shoal faced dissolved pore reservoir is mainly distributed in the Ⅳ 、 Ⅴforth-order sequence in the upper highstand systems tract, namely zero to forty meters of the upper Yijianfang Formation; The karst seam hole reservoir and cave reservoir could develop in Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ forth-order sequence in the whole Yijianfang Formation, but are mainly distributed in the Ⅲ 、 Ⅳ 、 Ⅴ forth-order sequence,especially in the Ⅳ、Ⅴ forth-order sequence. On the plane, beach facies erosion pore reservoir is only developed in bank body, and it may be affected by the paleogeographic constraints. The north bank body more easily developed this kind of reservoir. The karst seam hole reservoir can develop in the part of bank body and interbank, but with the features of the more development in the interbank, and showedclose relationship with fracture. The composite parts of bank and features are this kind of reservoir favorable development zone.