Study On Well Logging Responses Mechanism And Comprehensive Evaluation Technology Of Watered-out Reservoirs In The Ultra-high Water Cut Period Of Oilfield

After many years of development, Lamadian, Saertu & Xingshugang oilfields in Daqing placanticline have entered ultra-high water cut period. The reservoir properties and log response characteristics are changing constantly with the variation of injected solution and the development process. Log evaluation of watered-out reservoirs is of practical importance value, which is one of the main technical methods of study on reservoir description and remaining oil distribution.In view of the satus of oilfield development and production, this dissertation focused on log evaluation of the watered-out reservoirs in ultra-high water cut oilfield, aiming at quantitative evaluation of remaining oil saturation and water cut forcast, and technically meeting the needs of guiding for adjustment and study on log interpretation methods in stage with coexistence of water flooding, polymer flooding, ASP flooding. Based on the rock physics experiments and simulation analysis, log response variations mechanism in different drive modes for the mixed fluid resistivity, formation resistivity, spontaneous potential, and acoustic time are systematicaly studied. Qualitative interpretation methods are proposed to recognize watered-out reservois in consideration of different water property and physical property. In qualitative evaluation, a more applicable saturation interpretation model under different driving conditions is set up, which is based on effective medium theory. This study is highly systematic and innovative to some degree, the conclusions and understandings obtained are as follows:(1)The variation rules of log responses are closely linked with watered-out reservoir properties. Through physical experimental simulation of reservoir conditions and theoretical analysis, the variation rules of eletric property, acoustics and spontaneous potential under the different conditions of water flooding, polymer flooding and ASP flooding are systamatically studied. This is the foundation for the qualitative interpretation and quantitative evaluation.(2)Rock physics experimental results and pair-well data are integrated, and the differences of log responses in watered-out reservoirs with different water property and physical property are distinguished. Following the idea of“separation and step by step”, polymer flooding reservoirs, ASP flooding reservoirs and waterflooding reservoirs will be treated separately. Furthermore, research on waterflooded reservoirs can be conducted by applying overlapping method of porosity-resistivity log curves.On the basis of reservoirs classification or subdivision on thick oil zones, qualitative interpretation of the different properties can be realized effectively.(3)Based on effective medium theory, a mixed muddy sand calcium general effective medium resistivity model (SATORI) is established, which is the main innovation of this dissertation. The model applied principle of parallel conductance between laminated shale and dispersed shale sandstone, and the latter is divided into 6 compounds including sandstone particles, non-conducting oil and gas, dispersed clay particles, calcium particles, micro-capillary pore water and the mixed fluid. It shows that the model has strong applicability by analysis on simplified models and the conductivity precision between experimental measurement and calculation. The model applies to saturation evaluation not only for sands of different shale distribution, also the situation of conductive matrix, but also for watered-out zones interpretation under different driving conditions. In addition, through the introduction of percolation index and percolation rate to describe the factors of pore structure and fluid distribution, the model shows quantitative representation of a and b, which is the two parameters in Archie formula, and it gives the physical meaning more explicitly.(4)Through the conversion relationship between the reservoir water cut and the displacement efficiency, watered-out level classification and quantitative evaluation on thick oil layer subdivision can be realized. It is helpful to direct the adjustment and dig out potential in ultra-high water cut oilfields.