The Main Controlling Factors And Remaining Oil Distribution In Lowly Permeable Reservoirs With Small Complex Fault Blocks

It is very difficult to explore and develop low permeability reservoirs in small complex fault block, the recovery factor of which is usually low at present, the development effect of which is poor, and the remaining oil distribution of which is complicated with great tap potential of reserves. Take Fu3 Member reservoir of Taixing Oilfield in Qingtong Sag of Subei Basin as typically special example, the paper focuses on main controlling factors and remaining oil distribution of low permeability reservoirs of small complex fault block, recognizes underground features of this kind of reservoir, researches effective development methods and development countermeasures, and makes reasonable and scientific schemes for potential tapping to obtain higher recovery factor through comprehensive treatment, which have vital practical significance in improving the development level of hard-to-recover reserves of low permeability reservoir in small complex fault block to realize the resource substitution.The remaining oil distribution has been researched in main controlling factors, fine reservoir description, fine reservoir numerical simulation, and so on; and the potential tapping countermeasures have been discussed in the paper. Based on main controlling factors of reservoir, the fine reservoir description has been researched. Through fine stratigraphic correlation and interactive 3D seismic structure interpretation, combined with production performance data, determining internal low grade faults by dynamic and static comprehensive recognition technology, the fine structural model has been established, the fine reservoir research has been made, the distribution of sedimentary micro-facies and sand body has been deeply analyzed, and the combination has been strengthened between reservoir engineering technology and dynamic analysis. Through qualitative and quantitative description of remaining oil distribution based on main factors influencing remaining oil distribution, reasonable potential tapping countermeasures have been made in view of remaining oil distributing features.Some distinguishing methods and technologies have been used in the research:during research in structure, making full use of the drilling, well logging and seismic data, and combination of well logging and seismic lay a foundation for migration and combination of low grade faults of small complex fault block reservoirs and accurately specifying the structure, through geological calibration and interactive fine seismic interpretation; during research in reservoirs, subdividing the reservoir unit into single sand body, the comprehensive description has been made in category, lithofacies, lithologic character, distribution range, morphologic characteristics, pore structure and changes in physical properties of oil stored in reservoir rocks; based on fine reservoir description, the reservoir model has been established, and distribution laws of remaining oil have been found out, combining with dynamic monitoring and by using of fine numerical simulation. The fine research degree is a prerequisite of key technology to realize scientific and reasonable development of low permeability reservoirs of small complex fault blocks.By comprehensive treatment advice of the article, the exploited effect of small complex fault block and low permeability reservoirs can be evidently improved. Encrypting and modulating the brunt fault block, the result of exploited was evidently straighten up, the output increased, the harvest rat of water expel oil visibly advanced and the inefficient fault block resumed Normal production through scattered modulated.The cognitions obtained include:(1) multiphase tectonic activities of Subei Basin and mutual cutting of faults are main controlling factors for forming of small complex fault block reservoirs; (2) the distribution and productivity of oil and gas underground are directly controlled by lithofacies, distribution range and pore structure of reservoir rocks and changes in reservoir physical properties, which are important factors to form low permeability reservoirs of small complex fault blocks; (3) in the developed parts of fault system, the fault block is broken, complicated, and of small size with low control degree of primary well pattern reserves usually, which is main enrichment area of remaining oil distribution; (4) the transition zone of sedimentary micro-facies is important enrichment area of remaining oil distribution, with serious reservoir heterogeneity and low sweep degree of water flooding; (5) the fault system is the main controlling factor to form low permeability reservoirs of small complex fault blocks, and the low grade fault is the main controlling factor of remaining oil distribution of this kind of reservoir.