Research On Interpretation Method Of RPM Logging In Offshore Heavy Oil Reservoir

At present, more and more thickened oil sandstone reservoirs are put into production in the offshore, How to improve the recoverable reserves has become to the most important issue of research. The L oilfield which was a typical heavy sandstone reservoir has entered the high water cut stage. But with the extension of time of injection, the production gradually decreased and the composite decline rate was about14%. With some general profile control measures were taken by the Phase Ⅰ wells, to some extent, these controlled the water’s speed and increased the oil production and the composite decline rate dropped to8%. Though a certain amount of research results has been got, it needed to further study the impact of factors of remaining oil distribution and establish research methods about the residual oil distribution in the offshore heavy oil reservoir.These could offer potential methods and technical means to find out the remaining oil in the offshore heavy reservoir.In the home and abroad, the advanced residual oil saturation logging technology are RST, RMT, PNN, PND and RPM. The onshore oilfield such as Turpan-Hami, Liaohe, Shengli, Zhongyuan, Dagang always applied RST RMT, PNN and PND to monitor the reservoir level of exploitation, determine the reservoir flooding level and understand the block remaining oil distribution. The RPM is a kind of residual oil saturation logging Miriam which is launched by Atlas.And its casing radius is a minimum of43mm and it can endure high temperature and high pressure, the best performance can reach to177°C and137MPa.What is more,the tool had the best energy resolution of6.5%.In domestic, only China Oilfield Services Division has introduced the RPM instruments. It mainly used to determine oil saturation, gas saturation, oil, gas and water interface changes, and then it is good for remaining oil distribution in the offshore oil and gas field and achieved good results.This paper described the working principle of the residual oil saturation logging tool and they were compared to other tools. And it summed up the advantages and disadvantages between them by analyzing the similarities and differences. It mainly discussed the structure, measuring principle, instrument parameters, five measurement modes and applications of the RPM logging. Also, the article combined with reservoir and geological characteristics to analyze the applicability of two main mode.There are a variety of influential factors such as borehole environment and complex formation lithology during the measurement of RPM logging tools. It needed analysis and correction in order to reflect the true formation information. The paper combined with the special well structure of the offshore heavy oil reservoir to design volume model of the influential factors about the argillaceous, calcareous, gravel pack, casing size, wellbore fluid and other factors. As a result, it deduced correction formula about univariate and multivariate factors and established the theoretical plates. By analyzing the differences between before and after correction, it could provide a theoretical support for the remaining oil evaluation techniques.Due to the inaccuracy of measuring heavy oil in the laboratory, we can not study variation of the count rate by the traditional method. The article used downhole scale technology to change the RPM Wellsite calibration method to the field calibration method. Firstly, it converted wellhead flow into underground flows by fluid parameters. Secondly, it calculated water holdup using the slippage model and calculated the water saturation by the relationship between moisture content and water saturation.The relationship was obtained by the relative permeability data. Finally, it drew the RPM theoretical scale plate by the actual measured results.According to the characteristics of the reservoir, the article interpreted and evaluated the remaining oil of the offshore heavy oil by combining with RPM logging data, it is consisted of the results of before and after correction, then, the results were verified by the production profile, flooding levels and classification standards. Before the correction, the coincidence rate was only45%, but the rate increased of70%after the correction. The research showed that in order to improve interpretation accuracy, the influential factors such as lithology, borehole and density should be corrected. At the end, a saturation evaluation method of the residual oil which is fit for the offshore heavy oil reservoir was formed.