Logging Evaluation On The Low Resistivity Oil Reservoir In Bohai Oilfield

Because of complex origin mechanism and geological conditions of low resistivity reservoir, it's identification and evaluation of low resistivity reservoir is very difficult. Taken into account of its subtle and enormous exploration potential, in-depth study in the causes, identification and evaluation of low resistivity reservoir is necessary.In this paper, with the help of logging, testing for oil and core analysis experiment information of Low-Ming Group, Guantao Group and Dongying Group in Bohai Bay A,B,C oilfields, included more than 40 wells, we make clear the geological features of this region and obtain the differences between high resistivity reservoir and low resistivity reservoir from lithology, physical properties, electrical properties, micro-pore structure and formation water characteristics. So we achieve the purpose of geological and micro-perspective cause of low resistivity.By analysis of the causes and logging features in study region, low resistivity reservoirs can be divided in two types: first is due to fine lithology and high shale volume. Through the deep resistivity-acoustic and deep resistivity-the ratio of two cross plates can identify fluid property of such low resistivity reservoir effectively. Being assistant role, two curve overlapping methods can quickly identify oil and water. One is full saturation water in flushed zone resistivity curve, and the other is the reconstructed spontaneous potential curve. Another type is caused by thin layer of sand and shale. The cross plot of deep resistivity and spontaneous potential can identify this type reservoir. Besides, wavelet multi-scale energy spectrum analysis can better identify the fluid of thin layer reservoir. Combined with the advantage of MDT sampling and pressure data and NMR logging,we establish a method by conventional logging and new logging technology in fluid identification of low resistivity reservoir.According to the results of CoreLab Corporation, we established bound water saturation model based on the neutron density difference and total porosity. The calculation of water saturation by W-S model in Ming and Guantao group is effective. In the model, m*and n* are obtained from CoCw, Formation Factor and Resistivity Index experiments. The calculation of Qv is based on clay mineral composition model. B value is selected by taking into account the factors of temperature and salinity, in the help of Waxman and Thomas's new results. In Dongying and Shahejie group Dual Porosity Model achieve a better result.The methods in the paper were practical applied in Bohai Oilefield. It was testified practically and effectively. The paper provides some important clues and methods. The interpretation coincidence rate was significantly improved, and we achieved the desired purpose.