Study On Formation Mechanism And Evaluation Method Of Complex Fault Block Low Resistivity Reservoir In Sudan Area

Low resistivity reservoir is a kind of complex reservoir,and it has great significance to study the genesis,identification,evaluation and development.However,due to the various complex types of low resistivity reservoirs,the identification and evaluation of this type of reservoirs have been quite difficult.Therefore,it is necessary to study the mechanism and evaluation low resistivity reservoirs.Low resistivity reservoirs of freshwater argillaceous sandstone have commonly developed in the Muglad basin.Therefore this feature brings great difficulties to the log interpretation.The geological and petrophysical causes of low resistivity have been analyzed based on the logging data,mud logs,core analysis data and production test of Ghazal,Aradeiba and AG formation in Muglad Basin,Sudan.Geological causes are mainly analyzed in sedimentary and tectonic characteristics.The result has shown that the petrophysical causes consist of the additional conductivity of clay,high immovable water saturation,the salinity of formation water,the conductive minerals,the saline drilling fluid invasion and sand-shale interbed.According to the type of low resistivity genesis in this studied area,the identification and determination of oil and water layer were established by cross plots of resistivity-porosity,water saturation-porosity and resistivity-?SP.At the same time,Modular Dynamics Formation Tester(MDT)data were used to identify the fluid properties and determine the oil-water contact,and the low resistivity reservoir was further identified by multiwell correlation and reservoir profile evaluation.Saturation evaluation models for different mechanisms were established based on Indonesian equation,J function and W-S model.The results show that the J-function is better in Ghazal and Aradeiba,while the W-S model has better effect in AG formation.These evaluation methods of low resistivity reservoirs are effective in the exploration and development of N and K fields,and the interpreta tion rate is improved obviously.This improvement has laid the foundation for the evaluation of oil reservoirs in the later stage of development and has achieved the expected targets.