Research On Prediction And Evaluation Techniques Of Tight Oil Reservoirs In Jimsar Sag, Junggar Basin

The Jimsar sag in the eastern part of Junggar basin is a typical continental tight oil exploration potential area which has been discovered in China. Source rocks are widely distributed in target layer of Permian Lucaogou, in which dolomitization rock reservoirs are developed in mutual ways and continuous distribution. And symbiotic relationship between source bed and reservoir bed make it possible to have the characteristics of source-reservoir one body being wholly petroliferous which have a great resources and large exploration potential. Due to restriction, for example, the tight oil reservoir in this area has low porosity and very low permeability; oiliness is controlled by "dessert" reservoir wih high dolomitic and sandy; the preliminary study is influenced by the quality of seismic data; multi mineral lithology is too complex; rock mechanics parameters characterizing difficult etc, it is difficult to accurately evaluate the tight oil reservoirs in this area in which the exploration direction and favorable zones are unclear; the drilled wells have low deliverability; drilling deployment lack the technical support. Therefore, it is an urgent problem to find an effective geophysical techniques to evaluate the tight oil reservoirs and improve reservoir production capacity in the study area.To solve the above technical problems, and promote the deployment of exploration in the study area, according to international standards on tight oil reservoir evaluation, this paper introduces some geophysical evaluation techniques and methods from 6 aspects, which combines characteristics of tight oil in Jimsar depression. On the basis of complex and multi mineral rock modeling and mechanical character, it is formed a series of tight oil reservoir prediction technology that make post-stack geostatistical inversion and pre-stack elastic parameters inversion as the core. Those technologies have effectively supported the exploration and production, and achieved a wealth of technology and exploration results:(1) Porosity can be predicted by using geostatistical inversion based on the multi-attribute neural network, which can effective evaluate reservoir quality, and we can get favorable reservoir range in which effective porosity is more than 8%.(2) This study completed the curve prediction of total organic carbon content by study on the evaluation method of total organic carbon content by using well logging information, and completed the prediction of the total organic carbon content of the source rocks which evaluated the hydrocarbon generation conditions effectively by combined with pre-stack elastic parameter inversion technique. The effective source rock TOC content is more than 4% in the forecast result.(3) This study completed the prediction of the abnormal high pressure zone by using formation pressure prediction technology by high precision horizon velocity control method.(4) This study conducted a series of contrast experiments with different prediction methods, and completed the reservoir prediction of brittleness on the basis of pre-stack elastic parameter inversion technique, through elastic characterization research of rock mechanics parameters. The predicted results with drilling self-agreement has reached 100%, which has become an effective evaluation parameter for the high yield of the project.(5) Based on the analysis of regional crustal stress, the horizontal stress difference prediction is completed, which has guiding significance to the development of horizontal well in engineering, by using the elastic characterization of rock mechanical parameters.(6) This study used the pre-stack and post-stack joint fracture prediction technology, with the using of anisotropic fracture prediction methods in the pre-stack all-round data, we completed the quantitative fracture explanation, and defined the relationship between fracture development pattern and productivity.Through the above methods, we formed a geological evaluation technology based on physical properties, TOC, formation pressure prediction, defined the favorable distribution areas of the upper and lower desserts which guide to choose the macro area of tight oil exploration; we also formed an engineering evaluation technology which takes the brittleness, the horizontal stress difference and the fracture as the core, defined the main control factors for the high yield of the project. This study completed the matching technology of tight oil reservoir evaluation in research area, and the application of comprehensive evaluation effected effective, which provides the basis for the late evaluation and development, and the guidance for planning the trajectory of horizontal wells.