Radial Resistivity Characteristics and Oil-Bearing Properties of Low-Permeability Reservoirs:A Case Study of the Chang 61 Formation of the Luohe Oilfield,Ordos Basin
s:The low-permeability Chang 6-1 reservoir in the Luohe oilfield of central Ordos Basin varies greatly in oil saturation and shows strong heterogeneity.In addition,the invasion of freshwater drilling fluid has also resulted in the uneven radial distribution and great variations of reservoir resistivity.This work performed comparative analysis of dual induction-laterolog 8 and array induction logging on the Chang 6-1 Formation.Results indicate that the radial resistivity of water layers is increased resistivity invasion,and the radial resistivity of oil layers and oil-water layers generally shows related trends of decreased resistivity invasion,low resistivity annulus and high resistivity annulus.The decreased resistivity invasion helps to identify the oil layers and oil-water layers of the high oil-saturation and high resistivity,while the low-resistivity annulus and high-resistivity annulus help to identify the oil-water layers of the low resistivity.The radial resistivity combination of dual induction-laterolog 8 in some oil-water layers displays increased resistivity invasion and low deep induction resistivity.It is speculated that it may be limited by the detection range of dual induction-laterolog 8,and is the result of freshwater drilling fluid invasion near the wellbore in low-resistivity annulus.The deep induction resistivity reflects invasion zone,rather than the oil-water layer,which is easily misinterpreted as a water layer.Therefore,the fluid properties in reservoirs with"increased resistivity invasion"characteristics and low deep induction resistivity in dual induction-laterolog 8 may be indicative of water layer or oil-water layer.It is necessary to combine deep detection logging data or reservoir geological characteristics to further analyze and improve the recognition rate of oil and water layers.
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