Research On Logging Evaluation Of Low Porosity And Low Permeability Reservoir In Gaoyou Depression

Low porosity and low permeability reservoir in Gaoyou depression has fine grain, poorreservoir property and complex pore structure. In order to solve the problem of low accuracyreservoir modeling, complex mud invasion characteristics, and difficult oil and water layeridentification in low porosity and low permeability reservoir of Gaoyou depression, theE2d1,E1f3and E1f1reservoirs are targeted as the main research objects to conduct researchingon reservoir well-logging evaluation.Reservoir characteristics and4-property relationship are studied. Reservoir are classifiedaccording to pore structure through analyzing of mercury injection and NMR experimentsdata. The porosity calculation models of different beds are established through corecalibration logging method and the permeability calculation models are established throughflow unit index method. Through systematic analysis of rock electric data under normaltemperature, the Archie variable element saturationcalculation models are built. Reservoir effectiveness is studied on the basis of reservoircharacteristics analysis and reservoir parameter modeling. Response characteristics of arrayinduction resistivity are simulated on condition of formation invaded by freshwater mudfiltrate. Invasion factor, which is able to reflect reservoir fluid, is put forward, with it’sinfluence factors and applicable conditions been discussed. Several fluid propertyidentification charts of low porosity and low permeability reservoir in Gaoyou Sag areestablished through multi-parameter fusion method.Analysis of petrophysical experimental data and well-logging data show that, reservoirpore structure of study area can be classified into five kinds. E2d1mainly develop the first typeof reservoir, E1f1mainly develop the third and third type of reservoir. The pore structure ofthis two reservoirs are relatively simple. With the increase of porosity,the formationcementation exponent m increase linearly. E1f3mainly develop the forth and fifth type ofreservoir. Its porosity distribute in a wide range with complex pore structure. There is animportant demarcation point in the relationship between formation cementation exponent mand porosity. When the porosity of E1f3reservoir is less than the boundary porosity, thecementation exponent m increase with the increase of porosity. When the porosity of E1f3 reservoir is greater than the boundary porosity, the cementation exponent m increase slightlywith the increase of porosity.Invasion factor is influenced by reservoir physical property, formation water salinity andoiliness of reservoir. In low porosity and low permeability reservoir, the invasion factor ofwater layer is obviously greater than that of oil layer when the formation water salinity isstable. The invasion factor of oil layer and oil-water layer decrease slightly with the decreaseof porosity and permeability of formation, and the invasion factor of water layer decrease firstand then increase with the reservoir physical property getting worse. When other conditionsremain unchanged, the reservoir invasion factor increase with the increase of formation watersalinity. Using invasion factor to identify oil and water layer requires the time of mudinvasion not too long, and it’s application effect is better in low porosity and low permeabilityreservoir.Fluid property identification charts are established through invasion factor, arrayinduction deep investigation resistivity, apparent formation water resistivity, as well as naturalgamma-ray relative value multi-parameter fusion method. And good effect is obtained in lowporosity and low permeability reservoir of Gaoyou sag.