Researches On The Analysis Method For Damage Mechanism Of Fluid To The Ultralow Permeability Oil Reservoir

Fracturing is an important means of oil exploitation, fracturing fluid damage is one of the evaluation methods, it is of great significance in improving development effect of ultralow permeability reservoir and the steady development of China oil industry to study the extent of fracturing fluid damage to ultralow permeability reservoirs. the formation damage caused by vegetable gum fracturing fluid includes damage from fluid loss and solids damages caused by solid residue.in this paper the low permeability reservoir core and core powder from Taiyuan group were taken as research object, to study the fracturing fluid damage; dye was taken as tracer to establish liquid damage analysis system,and test conditions were optimized; in the core flow experiment, fracturing fluid was labeled with tracer to trace the invasion depth of liquid and detect it; guar gum were degraded by hydrogen peroxide, separating it from core powder, degradation conditions were optimized, The optimum way of coloration in phenol-sulfuric acid method was investigated. Infrared spectrum analysis and UV spectrophotometer detection were chosen to test tracer absorbance as the evaluation measure. the conclusions of major work include the following:(1) The results of surfactants screening experiment and the optimizing experiments showed that:acid orange II was chosen as tracer, eluent with3%NaCl aqueous solution, the best surfactant is proved to be K12. Optimum elution conditions:elution time to be15minutes, centrifuged for15minutes, eluent K12concentration to be400mg/L, Eluted6times, Total Elution volume to be20mL. Under these conditions, the elution rate of acid orange II can reach about92%.(2) The result of core flow experiment:In hydraulic fracturing simulation conditions, the amount of immersion liquid decreases while thickness of the core increases, the amount of the invading liquid turn to zero at the penetration of15mm.(3) Optimum degradation conditions:3mL30%H2O2was added to50mL1000mg/L solution of guar gum and mixed, after setted at60℃for120min, MnO2solid powder was added at the mass ratio of MnO2/H2O2=1:7.5.(4) Using glucose as the standard, the optimum way of coloration in the process of deter mining degraded guar polysaccharides content by phenol-sulfuric acid method was as follows:added1.0mL5%phenol solution to2.0mL degraded guar solution and shaken. Then5.0mL concentrated sulfuric acid was added drop by drop quickly. After setted at60℃for50minutes, the solution was detected at wavelength of491nm.