Micro-geological causes and macro-geological controlling factors of low-resistivity oil layers in the Puao Oilfield

Low-resistivity oil layers are often missed in logging interpretation because of their resistivity close to or below the resistivity of nearby water layers. Typical low-resistivity oil layers have been found in the past few years in the Putaohua reservoir of the Puao Oilfield in the south of the Daqing placanticline by detailed exploration. Based on a study of micro-geological causes of low-resistivity oil layers, the macro-geological controlling factors were analyzed through comprehensive research of regional depositional background, geological structure, and oil-water relations combined with core, water testing, well logging, and scanning electron microscopy data. The results showed that the formation and distribution of Putaohua low-resistivity oil layers in the Puao Oilfield were controlled by depositional environment, sedimentary facies, diagenesis, motive power of hydrocarbon accumulation, and acidity and alkalinity of reservoir liquid. The low-resistivity oil layers caused by high bound-water saturation were controlled by deposition and diagenesis, those caused by high free-water saturation were controlled by structural amplitude and motive power of hydrocarbon accumulation. Those caused by formation water with high salinity were controlled by the ancient saline water depositional environment and faulted structure and those caused by additional conductivity of shale were controlled by paleoclimate and acidity and alkalinity of reservoir liquid. Consideration of both micro-geological causes and macro-geological controlling factors is important in identifying low-resistivity oil layers.

A method of seismic meme inversion and its application

Under the condition of thin interbeds with great lateral changes in terrestrial basins,a seismic meme inversion method is established based on the analysis of seismic sedimentology technology.The relationship between seismic waveform and high-frequency well logs is established through dynamic clustering of seismic waveform to improve the vertical and horizontal resolution of inversion results;meanwhile,by constructing the Bayesian inversion framework of different seismic facies,the real facies controlled inversion is realized.The forward model verification results show that the seismic meme inversion can realize precise prediction of 3 m thick thin interbeds,proving the rationality and high precision of the method.The application in the Daqing placanticline shows that the seismic meme inversion could identify 2 m thin interbeds,and the coincidence rates of inversion results and drilling data were more than 80%.The seismic meme inversion method can improve the accuracy of reservoir prediction and provides a useful mean for thin interbeds prediction in terrestrial basins.