Forming Mechanism Of Low Resistivity Pay Zone In The Shallow Heavy-oil Reservoir And Its Identification Methods

The ongoing exploration in the Jiuqunan Qigu Formation heavy-oil reservoir, which is located at the Karamay Oilfield in the northwestern margin of the Jungger Basin, revealed that heavy-oil occurs in some pays collected from drilling core, which is of lower logging resistivity than interpretation standard for poor oil-bearing reservoirs. Analysis indicates that they are of the potential of oil reservoir, and further research also confirms the occurrence of shallow low resistivity pay zones in the studied area.Based on the forming characteristics and settings of shallow heavy-oil reservoirs, and combined with sedimentology, geology, lithological and logging physics, well test, production test and core experiment: from the macroscopic view, this dissertation analyzed sedimentation of the Qigu Formation J3q3 reservior pays and the control factors including reservoir sediment, micro-amplitude structure and reservoir model and their control on the formation and distribution of heavy oil low resistivity pay zone; from the microscopic view, it also discussed the influencing factors as characteristic of reservoir rock, clay minerals, conductivity minerals, pore texture and type; and analysed the influence of the bound water saturation, salinity of stratum water and oil viscosity.The results shows that low resistivity heavy oil reservoirs in the Jiuqunan Qigu Formation are mainly controlled by the additive electric conductivities of clay, high water saturation, conductivity minerals(pyrite), and oil viscosity.①the reservoir locate in foreland subfacies and flatland subfacies of braided channel delta, its rock is fine and contains more clay minerals, enhance the ability of clay additional conducting, result in the lowing of resistivity;②the reservoir is a secondary shallow heavy-oil reservoir, and locate in a low amplitude structure area, result in high stratum water content and high water saturation, result in the lowing of resistivity;③a large number of authigenic pyrites formed in diagenetic stage and later is an important factor of forming the lowing of resistivity;④high viscosity heavy-oil lead to high resistivity, in the area of low viscosity forming a relatively low resistivity heavy-oil reservoir.For using existing logging-data and easy to find the low resistivity heavy-oil reservoir in other oil fileds, this paper rebuilt the model of logging interpretation with Jiuqunan general logging-data, well test data and production test data. Confirmed DEN is an important parameter to identify the low resistivity heavy-oil pay. Provied quantitative and semi-quantitative identify methods. Researched and predicated the distribution of low resistivity heavy-oil pay in vertical and plane in Jiuqunan area.The above study solved the geological problems of shorting heavy oil production capacity in rolling development and broaden the idea of looking for heavy-oil in Jiuqunan. Provided new reliable theoretical basis and effective methods to evaluate low resistivity heavy-oil pay in adjacent area. The research applied to the production of oil field, so that the low limit RT standard of oil discriminant from 28Ω·m down to 13Ω·m, added oil-bearing area 10.2km~2, added proved reserves 1500×10~4t, has made great economic and social benefits.