The Reservoir Evaluation Of The Upper Section Of Sha-4,Third And Fourth Sand Group In Yi176, Shengli Oilfield

Yi176block is located in Yi176-Bo Shen-4fault-terrace belts of Bonan oil field, Bonan depression, faults in rockmass are developed in the project area. Two main sub-E-W-faults passed through the study area and locally north-south little faults. On structure it is a northeast leans’structural nose, which displays northwest and southeast low, the middle is high. The target strata of research area is the upper section of Sha-4, third and fourth sand group. The depth is between3200m-4500m, with area of49.8km2depth of3200m-4500m and18wells, which has good oil shows.Glutenite reservoir is an typical reservoir type in Yi176block, and which has superior hydrocarbon accumulation conditions, however, the third and fourth sand group in upper section of Sha-4reservoir has low-ultralow porosity and ultralow-extremely low permeability, many complex geological conditions are gradually expose, such as deep burial, strong faults, the insider structure complicated, complicated spatial distribution of reservoirs. In this paper, using the related theory of petroleum geology as a guide, reservoir characteristic of sedimentary micro-facies, petrology, diagenesis, physical property and heterogeneity of the third and fourth sand group in upper section of Sha-4reservoir in Yi176block are studied, classified and evaluated. And then point out the favorable exploration target, lay a significant geological foundation for the further improve oilfield exploitation benefit.Based on the core observation and integrated logging data interpretation, adopting the hierarchial control, stratigraphic circle correlation, the contrast of equal thickness and marker beds correlation, applying point, line and surface trinity method, the isochronous stratigraphy framework of strata of18wells are fine divided and correlated, and fine model of single layers is also established.. We divided the third sand group into9layers, the average8.9m to14.3m, and the fourth sand group into9layers, the average10.4m to15.3m.By contrasting the plane distribution of quartz, feldspar and lithoclast contents, the extraction of RMS amplitudes, sand group sandstone thickness contour map, fine sandstone, siltstone conglomerate isopach map and percent content map, the studis show that the main deposit sediment of third sand group in Yi176area came from the north Chengdong Uplift, and there is also a minor source from east Gudao Uplift. Fourth sand group came from the south Chenjiazhuang Uplift, a minor source from north Chengdong Uplift, Gudao Uplift in the east of researched region have a low impact. Two different provenance systems displays in the sedimentation period the Sedimentary environment changed.Through the core data, log analysis, particle size analysis and regional geological background, macrofacies types and sedimentary evolution rule are discussed. We determine that the research area is a lacustrine facies--fan-delta facies depositional system. Littoral and shallow lake and fan-delta front subfacies are a major type of sedimentary subfacies of the third sand group. Fan-delta front subfacies is the fourth sand group. The most important reservoir sand is beach bar in Littoral and shallow lake subfacies and distributary and subsea distributary sands in fan-delta front subfacies.Analysised the reservoir rock characteristics and diagenesis of the characteristics of in-depth and meticulous. Studies have indicated that the sandstones are main lithic arcose sandstone, there is also a small amount of feldspathic lithic sandstones, and the composition maturity of target zones is on a low side. The main diagenesis of the reservoirs in the study area includes compaction, cementation, metasomatism and dissolution, etc. which belongs to stage A of middle diagenesis phase. Compaction and cementation change the physical property to worse, although the dissolution of unstable mineral, such as feldspar, is commonly seen, for the dissolved degree is weak, dissolution contribute a little to form secondary pores.Reservoir pore type are mainly original intergranular pore, followed by intergranular dissolved pore, feldspar solution pore, Lithic solution pore, mould pore, microcracks etc. The main throat type is micro throat and lamellar throat.The pore structure is difference between different microfacies, underwater distributary channel and beach bar with better pore structure, followed by sand sheet and shore sand. The reservoir permeability in study area is poor overall.Based on the studies of sedimentary characteristic, reservoir characteristic and diagensis, factors effecting reservoir physical property have been analysed and mainly controlling factors causing reservoir densification have been discussed. The studies show that sedimentation, diagensis are the main factors controlling reservoir physical property development. High content of unstable component of clastic grains, such as feldspar and debris, and matrixs, sharply porous diminution caused by compaction and cementation, and lack of secondary pores jointly lead to reservoir densification.On the base of qualitative analysis, the study select characteristic factors including porosity, permeability, sedimentary microfacies, diagenetic facies type and sandstone thickness. There are4reservoir categories in the study area, that I is favorable reservoir, Ⅱ is less favorable reservoir, Ⅲ is moderate reservoir and IV is poor reservoir. I and II are mainly developed in the beach bar and underwater distributary channel. Comprehensive analysis of the two sand group, fourth sand group reservoir is better.The main reservoir types in study area are fault block reservoir, lithologic reservoir and composite reservoirs, which is controlled mainly by tectonic, lithologic and physical character differences. On the base of above studies, combined the distribution of oil and gas, the criteria of reservoir evaluation, this paper predict32favorable reservoir development area in different members.