Research On The Reservoir Characteristics Of Middle-deep Strata In Shahejie Formation Of Baxian Sag And Its Main Controlling Factors

In this paper,Shahejie formation third section and Shahejie formation fourth section(>3000m)storage reservoirs in the middle-deep strata of Paleogene in two tectonic belts,including Wenan slope belt and Chagaomao steep slope area in Baxian sag of Jizhong depression are taken as the main objectives of research.On the basis of the research performed by predecessors,through utilization of the collected data of earthquake,well boring,well logging,rock core,testing and development,etc.,comprehensive research is performed to the reservoir characteristics,the main controlling factors for the development of middle-deep strata reservoir are analyzed,so as to reach the aim of evaluating and predicting reservoir,and the following main achievements and cognition have been obtained:(1)The zone of research manifests the petrology characteristics of high content of feldspar and rock debris mainly contained in rock debris sandstone and sandstone,the grain size is mainly fine-micro sand,the sorting is mainly good-medium,the rounding is mainly subround,subround-subamgular and subangular,the interstitial substance is mainly carbonate cement,which mainly includes calcite cement and also includes dolomite,and the impurity content is generally less than 15%.(2)Wenan slope belt in Shahejie formation third section and Shahejie formation fourth section of Baxian sag is a storage reservoir that mainly has mesopore-low porosity and extra-low permeability-ultra-low permeability,and Chagaomao region is a storage reservoir that mainly has low porosity-extra-low porosity and extra-low permeability-ultra-low permeability;in the planar direction,the physical property of Wenan slope belt is better than that of Chagaomao region.In the longitudinal direction,the physical property integrally becomes poor with the increase of depth,among them,the physical property of feldspathic silicarenite is the best,that of rock debris sandstone is secondary and that of feldspathic rock debris sandstone is relatively poor.(3)The category of reservoir space is mainly induced porosity,the reservoir space of the storage reservoir in the steep slope belt with less than 3500 m of burial depth is mainly mixed porosity,and the relative content of induced porosity is about 40%,the reservoir space of the storage reservoir with greater than 3500 m of burial depth is induced porosity,and the relative content of induced porosity is greater than 50%;development of small quantity of micro crevice is visible.(4)Now the storage reservoir of middle-deep strata of Paleogene is mainly located in periods A and B of middle diagenesis,and the category of diagenesis mainly includes compaction,cementation,metasomatism,dissolution and recrystallization,etc.;the grain size and relative content of mineral component are important factors that affect the porosity of the storage reservoir of clastic rock,through evolution up to now,the physical property of the fine-grained feldspar sandstone with relatively coarse grain size and relatively high content of feldspar is the best,that of fine-grained rock debris feldspar sandstone is secondary,and that of silty rock debris feldspar sandstone is the worst,that means the fineness or coarseness of grain size is more important than the content of feldspar,and it is one of key factors that constrains the porosity evolution of the storage reservoir in the area of research.(5)The anisotropy of the storage reservoir of Baxian sag is relatively strong.With the increase in the burial depth,the class of storage reservoir presents the overall trend of gradual worsening.In the longitudinal direction,the Shahejie formation third section at deep stratum of Paleogene in Baxian sag is mainly the storage reservoir of ?a and ?b category,and the Shahejie formation fourth section is mainly storage reservoir of ? and ? category;in the planar direction,the flat slope belt of storage reservoir class in the Shahejie formation third section of Baxian sag is better than than the steep slope belt.(6)Since there is abnormal pressure at the deep strata,the primary pore is kept,and belt with high abnormal porosity is commonly developed in the middle-deep layer.It is mainly developed at the middle lower subsegment of Shahejie formation third section,among them,the deep section of steep slope belt is about 3500~3800m and 4000~4200m,and the deep section of flat slope belt is about 2600~2800m and 3200~3400m.(7)In the area of research,the middle-deep storage reservoir in the flat slope belt is controlled by dominant sedimentary facies,early cementation and early oil and gas charging,the diagenetic denuation erosion is weak;the middle-deep storage reservoir in the steep slope belt is mainly commonly controlled by dominant sedimentary facies,stratum overpressure,denuation erosion and early oil and gas charging.Through comprehensive consideration to the deposition factor,physical property of storage reservoir and present situation of prospecting,prediction is performed to the favorable zone in the storage reservoir of Shahejie formation third section.