Low Porosity And Low Permeability Reservoirs Logging Evaluation Of Chang6 Oil-bearing Formation In Zhidan Oilfield

In recent years, low porosity and low permeability reservoirs have become one of the focus issues in exploration and development, and in increasing production and reserves. However, due to geological characteristics and complexity of log characteristics the low porosity and permeability reservoirs are facing some technology difficulties, which seriously impedes the recognition and assessment of low porosity and low permeability reservoirs and produces great difficulties for the rapid construction of large production.Taking chang 6 reservoir of Zhidan oil field in Ordos Basin for example, combining with some previous results, utilizing log data, geologic foundation data, analysis and test and production data and production performance data, setting out from the geological characteristics of the reservoir, aiming at the difficulties of lithology recognition, pore texture and logging responses complexity (low resistivity oil layer coexists with high resistivity water layer)of the low porosity and low permeability reservoirs, this research focus on the work and then make the achievements as follows:(1) Make qualitative and quantitative research of the pore structure and then on the basis of quantitative research discuss the reservoir classification. The study suggests that the quantitative integrated parameters(reservoir quality index and flow index) reflecting the pore structure characteristics is convenient for sort log evaluation and then analyze the correlation between the reservoir quality and flow index and capillary pressure curves parameters.The results show that the reservoir quality index better reflect the integrated low porosity and permeability characteristics of the reservoir. So in this research, in the constraints of capacity data,according to reservoir quality index we divide the reservoirs into four categories and do classification study on logging response characteristics of these four reservoirs.(2) In the premise of core calibration, do research integrated study of four-property relationship of reserviors.The results suggest that firstly high natural gamma ray existes in research area so it is higher clay content of sandstone calculated by the high natural gamma radiation. And natural gamma ray should be used with spontaneous potential method to identify lithology (shale content); Secondly, it has low precision to calculate physical parameters of reservoir directly from the porosity but in the classification of reservoirs pore structure, building classification physical interpretation model achieve good results; Thirdly, in study area part of the oil reservoirs have low resistivity.(3) We make the use of overlay method and the cross-plot method to identify the qualitative oil reservoir. The results show that the calculated SP-spontaneous potential measured overlay method and acoustic time- resistivity cross plot, the effect is satisfactory; British acoustic time-deep Induction electric rate overlay method in the low resistivity reservoir of the study area is insensitive.(4) On one hand calibrated sealed coring saturation analysis data and deduce that the loss of fluid for sealed coring related to reservoir quality index; On the other hand on the basis of study the reasonable classification and the reservoir characteristics, considering the 61 reservoirs in Zhidan oil field have the characteristics of development low-resistivity and shaly sandstone, combined with the test results of the CEC (cation exchange capacity), we have discussed the three suitable evaluation models for low resistivity reservoir with mud, acknowledge that:in the state of high salinity of formation water, CEC and Qv is not increased by high clay content, oil reservoir takes on low resistivity due to high salinity of formation water and its rapid changes in study area, consequently, Archie formula for the interpretation of the study area is still valid. However, in the litho-electric Experiment, we should be based on the formation water distribution and regional characteristics, use the salt solution which close to the formation water; in data processing, we can not force a to 1. Finally, we make the use of the calibrated sealed coring saturation analysis data and the dynamic production data to constrain and verify the physical properties of reservoir and quantitative interpretation model of the oil saturation, and have achieved good results.