Reason Analysis For Well Logging Curve Abnormality And Drilling Prevention Measures In Saertu Oilfield

Part of the tertiary adjustment well logging curve abnormality has appeared in newly-drilled block of Saertu oilfield, It is primarily that microelectrode and spontaneous potential curve occurred abnormal phenomenon, even some anomalous regions connect together and lead to well logging again. This article studies the abnormal curve characteristics of well logging response identification and classification by using microelectrodes and spontaneous potential logging theory, combined with the drilling block geological data and found out the reason for well logging cure abnormality. Through research it is the following understanding:Logging data show that well logging abnormality of microelectrode curve and the curve of natural potential is primarily, as well as a variety of well logging curve matching is not consistent. The main performance is that the microelectrodes magnitude of some permeable formation becomes smaller or even to zero, that the microelectrodes magnitude of some permeable formation becomes larger and sp magnitude becomes opposite direction (that is positive sp magnitude),that the curve of spontaneous potential in the non permeable formations (such as shale and oil shale) appears negative anomaly, that the ground line of sp curve in shale offsets distinctly.By studying the thickness of mud cake, mud electric resistivity, formation water salinity, the injected medium, formation pressure, fluid logging analysis and RFT technology,the main reason for well logging response anomaly includes polymer flooding, high formation pressure, lower resistivity of mud, mud cake thickness and the change formation water salinity.The principal reason causing well logging response change is the remained Polymer in pores, the degree of remained Polymer has a relationship with molecular weight. The well logging characteristics is that the microelectrodes magnitude after polymer flooding becomes larger and sp magnitude becomes lower and straightMicroelectrodes magnitude of the oil layer with good permeability and low pressure after polymer flooding becomes larger and sp magnitude becomes opposite direction as well as high pressure. The curve abnormality characteristics are similar. It can be separated by fluid logging. The density of drilling fluid become higher and the well logging response anomaly will become betterAfter drilling well the swirl generator can make the mud cake thin, the microelectrodes magnitude become larger, and the well logging response anomaly vanish. Lower mud resistivity makes microelectrodes magnitude lower, the mud resistivity can be improved by mixing with oil, the value of microelectrodes magnitude become larger effectively than before.