Study On Reservior Characteristics Of Shanxi Formation Of Daniudi Gas Field D47-D70

Daniudi gas field D47-D70 is located in the northeast part of north Ordos basin, the structural position of which is in the north part of Yishan slope.It is the key natural gas exploration and development zone of North China Branch of Sinopec. Shanxi formation is one of the key stratas in this area. Due to its complex geological conditions and diagenesis, the reservoir becomes densitifying and strong heterogeneity.The main factors controlling the reservoir development and gas accumulation characteristics are not clear,which hinder the gas field from the further development. Based on the petroleum geology, sedimentology, reservoir geology, logging geology theory as the instruction, using core data and its analysis data and testing, the characteristics of sedimentary facies and reservoir characteristics in the district were analyzed and discussed.Then the following points were made:1、Combining the traditional sedimentary cycles and high resolution sequence stratigraphy method,the original stratification of the 171 wells were reviewed in the district. The Shanxi Formation is divided into two members, namely shan 1 and shan 2. Shan 2 member is divided into two sand groups, namely S2-2 and S2-1; Shan 1 member is divided into three groups, namely, S1-3, S1-2 and S1-1.2、The studies for sediment source and sedimentary facies have suggested that the sediment source of shanxi formation mainly comes from the north east and it develops delta plain subfacies, including water distributary channel sand, crevasse splay, overflow and shore between bay microfacies.3、Petrological characteristics analysis showed that:shanxi formation mainly composed of lithic sandstone and lithic quartz sandstone.The sandstone has such characteristics as low compositional maturity、better particle separation、poor psephicity and sub-prismatic and sub-rounded edges. Pore cementation is the main cement type and some film-pore cementation also developed in the district. Micritic gray matter, clay and felsic are the main matrix. Dolomite, silica, calcite,and silica are the main cement.Both of them are the main types of fillings.4、By analyzing the cast thin, plain sheets and SEM data, we believe that the pore types mainly included intergranular pores, intragranular pores, the pores in the interstitial material, dissolution dissolution and fracture in the area.The intergranular dissolution pores are the main type and the secondary intragranular dissolution pores take the second place. The throat types can be divided into contraction, flake throat and micro throat and the micro throat and flake throat take the first place.5、According to the capillary pressure curve shape and the distribution of the pore structure parameters, the pore structure in the study area can be divided into four types. I class is lower threshold pressure, low porosity, low pore fine throat type, II class is low threshold pressure, low porosity, low permeability thin throat, III class is in the threshold pressure, low porosity low permeability micro throat, IV class is high threshold pressure low porosity low permeability micro throat. Daniudi Gas has complex pore structure and its parameters changed greatly.The value of the radius is relatively small, the displacement pressure is high, the maximum intake of mercury saturation is high, but the efficiency of mercury withdrawal is low, the effective porosity proportion in total porosity is small,the seepage ability is poor.6、According to analysis of the distribution and formation sequence of authigenic mineral, inclusion temperature, maturity of organic matter, the ancient temperature and a variety of diagenetic phenomena, we hold that the Shanxi Formation is in the A-phase of diagenesis in a whole.The reservoir develop patchy dissolution pores cementation diagenetic facies (Ⅰ diagenetic facies)), carbonate dense cementation diagenetic facies (Ⅱ diagenetic facies), clay dense cemented diagenetic facies (Ⅲ diagenetic facies), dense compacted diagenetic facies (Ⅳ diagenetic facies). The diagenetic facies of the main producing reservoir zones in the area overall are Ⅰ diagenetic facies and Ⅱ diagenetic facies. Ⅲ diagenetic facies reservoir has relatively poor productivity, IV diagenetic facies reservoir productivity is too poor to form industrial gas reservoirs.7、The main factors affecting the reservoir properties in the study area are as follows:sedimentation and diagenesis. Deposition mainly includes micro facies, clastic components, carbonate cements and fillings. Water distributary channel microfacies has the best reservoir property, followed by micro-phase crevasse splay. Feldspar and lithic content in the clastic components and physical property has certain positive correlation; Carbonate and filler content are negatively related with physical property. Diagenesis includes compaction, cementation, dissolution and metasomatism. Compaction, cementation and metasomatism made the reservoir properties worse, but the dissolution increased the porosity and permeability of the reservoirs.8、Using the lithology、physical、electrical、gas-bearing and other criteria to determine floor of the effective thickness,the results show that Shanxi Formation gas reservoir has such floors as 5% porosity、0.1mD permeability and 45% gas saturation.9、Using the lithology, porosity, permeability, median radius, displacement pressure, diagenetic facies, microfacies, effective thickness, gas saturation and unimpeded flow as characteristic parameters of reservoir comprehensive evaluation, the reservoir of the area was studied. According to the overall performance,the reservoir can be divided into the first class,the second class, the third class and the forth class.In this area,Shanxi reservoir give priority to the third class and the forth class,the second class taking the second place and the first class small.