Evaluation Of Tight Sandstones Of Chang8~6Intervals In Jiyuan Field Of Ordos Basin

Jiyuan oilfield has been found in recent years with an annual production capacityof more than one million tons of oil, which located in the western Ordos basin. Due tothe plenty of source rock, it has made up more than one oil pools from bottom to top inYanchang and Yanan Formation. Not only has it a better exploration prospect, but alsohas become the productive oilfield in Changqing oil field in recent years. YanchangFormation is a typical of low porosity and permeability reservoir. Due to the structure issmooth, the control of structure to the oil and gas accumulation is not apparent. Oil andgas is mainly distributed in higher permeable reservoirs in the tight reservoirs.Therefore, use of reservoir evaluation technology, and to select the high qualityreservoirs has to be the key of exploration and development in the future.Through core analysis and field investigation, and combination of using theancient flow, heavy and light mineral and other methods to conduct a research onsediment source of Chang8-6Formation. On the basis of core observation, andcombining with drilling data and achievements on studying sediment source,establishing Chang8-6Formation of small layers of sedimentary microfacies andsandbody distribution. Using microscopic study, SEM, EDS and lots of petrophysicaldata study the control factors of reservoir quality in Chang8-6Formation. Though theresearch of the relationships among lithology, porosity and permeability characteristics,electric properties and oil-bearing properties, analyzing the reservoir range and thereasonable reservoir classification standard, and reservoir prediction.The results of the study show that:(1) Chang8Formation to Chang6Formation,the sediment source is distributed gradually from the Alxa ancient land to Yinshanancient land. Because of the study area is located in the western basin, and Alxa ancient land is close to it, while Yinshan ancient land is far from it. Thus, Chang8Formation ismainly controlled by Alxa ancient land with delta plain developed. Chang6Formationis mainly constrained by Yinshan ancient land with delta front developed.(2) Highquality reservoirs are bond with chlorite coating and dissolution of feldspar. Feldspardissolution mainly appears in delta plain, followed by delta front, and chlorite coating isconstrained by Yinshan ancient land obviously with developing in the delta front.According to the reservoir evaluation results, combined with the diageneticdistribution and well tests and production tests, we can predict the exploration areas,and provide geological basis for the next exploration and development.