The Research On Damage Mechanism And Control Technique In Fractured Ultra-low Permeability Sandstone Oil Formation

The reserve of low permeability oil and gas reservoir is in big proportion of the reserve constitute in our country, the exploitation potential of low permeability reservoir is high. The ultra-low permeability sandstone oil formation has the common characteristic with low porosity, ultra-low permeability, fracture exist, severe heterogeneity, which is very easy to be damaged influencing the timely discovery and exact evaluation of oil formation. Therefore, the research of formation damage is of significance in the exploration and exploitation of this reservoir.The thesis is supported by the project from East China Branch of Sinopec, named Formation Damage Control Technique Research in Changling Sag, South Songliao Basin. The specific object of research is K₂qn², K₂qn¹ and K₁q⁴ in Yaoyingtai zone. The ultra-low permeability sandstone formation of research tract has amount of natural productivity, but the formation damage in the process of drilling and completion makes the initial production of well reduce at extremely low level even zero.The means of SEM, XRD and intrusive mercury data analysis are applied to study the reservoir characteristics and potential damage factors. The characteristics of formation cover low porosity, ultra-low permeability. The average porosity of formation is 10.73%; the average permeability is 8.55×10^-3μm². According to intrusive mercury data analysis, the throat is thin; R₅₀ is from 0.01μm to 0.54μm. The observation of core indicates the average density of fracture is 0.25 pieces per meter; the result of simulation experiment shows the average width is from 19.94μm to 23.26um under the in-situ stress. The type of clay mineral is very different in different team. Chlorite and illite mainly can be seen in K₂qn², illite mainly can be seen in K₂qn¹, the content of illite is biggest and that of illite/smectite mixed layer mineral is bigger in K₁q⁴. The mainly potential damage factors include sensitivity mineral, fracture and so on.The sensitivity damage degree is indicated through sensitivity experiment. The velocity sensitivity, water sensitivity, salinity sensitivity, acid sensitivity and alkali sensitivity are weak to moderate respective. The stress sensitivity of matrix is weak, while that of fracture is severe. The result of static and dynamic damage experiment shows the severe damage of additive and drill-in fluids in field. In a word, the major damage mechanisms contain sediment of solid grain, stress sensitivity and particle migration as a result of invasion ofsolids and liquids.The applied screen temporary plugging technique application software is programmed firstly, according to the thought of screen temporary plugging technique. Match the granularity curves of different proportion temporary plugging additives to propose optimal temporary plugging program. The temporary plugging drill-in fluid system is selected through temporary plugging laboratory experiment, so that the project of formation control technique is brought forward. The field trial of 3 wells is completed in person. The field application indicates that the application of the temporary plugging techniques not only reach the goal of the timely discovery and exact evaluation of oil formation, but also enhance the production of well directly or indirectly.