Researching On Characteristics Of Chang-7 Tight Oil Reservoir In An-83 Area,Xin'an'bian Oilfield

A set of tight sandstone reservoir of the Chang-7 oil reservoir in An-83 area of Xin'an'bian region in the Ordos Basin is a typical tight oil reservoir. The tight oil reservoir in this area is mainly characterized by self-generating and self-preserving and "source control". Lacustrine delta front sub facies are the sedimentary background, the main reservoir sand body is the main reservoir of the underwater channel, the hydrocarbon source rocks is lacustrine dark mudstone and oil shale, all above these have a good relationship with the superior reservoir cap combination. Chang-7 reservoir group was divided into Chang7₁, Chang7₂ and Chang7₃ three small layers. The signs of these small layers are clear, the sedimentary cycles are noticeable, and the thickness of the strata is stable. Chang7₂ sand body is the most developed, and the physical properties are relatively good, and the oil content is best. The Chang7₁ is the second. Chang7₃ small layer is mainly composed of lacustrine mudstone.By large amount of observation of the core, and the Laboratory experiment, combining with Scanning electron microscopy?SEM?, Cathodoluminescence, Conventional mercury, and Nano-CT scan, we obtain that the main sandstone type of the researching area is Lithic feldspathic sandstone and a small amount of Arkose, whose main storage space is the Residual intergranular pores and the Feldspar dissolved pores. The compaction and dissolution effect have significant influences on the process of the reservoir forming, especially the dissolution effect makes great contribute to the reservoir. The main ingridients of the clay minerals of the reservoir are the Kaolinite, Chlorite, Illite and the mixture of the Montmorillonite, which belongs to the A level of the middle diagenetic phase. In veiw of the significant differences between the tight oil reserviors and conventional low and Ultra-low permeability reserviors. We use two kinds of Characterization Methods, including conventional mercurcy injection and Nano-CT scan. By the experiment of conventional mercurcy injection, we find that the tight oil reservoirs have the characters of the bad Pore throat structure, good sorting, Fine skewness, tiny throat, and high displacement pressure. The results of the Nano-CT scan show that Reservoir pore radius distribution mainly range from 2 to 10?m, which can be considered as the Nano-throat. It has the attribution of Poor connectivity and complex structure, which is the key features of the tight oil reservoir. Based on Related parameters, we build the Criteria for the classification of the reservior and divide An 83 into three types of reservoirs.Matrix seepage is the main way before the reservoir is transformed. But, after reservoir volume fracturing, the reservoir shows the characteristic of the double porosity and fracture. The study shows that the difference of the percolation ability of the two is very large. The permeability of matrix is very low, the oil-water two-phase flow ability, fracture system of high permeability, oil-water relative seepage ability. Micro cracks have a certain role in promoting the reservoir physical properties, but the overall contribution is not large. The initial production of oil well fracture can be obtained with high yield, but in the later stage of mining, the reservoir is mainly based on the seepage flow of the matrix, and the decline of the oil well is low yield.