A Comprehensive Formation Evaluation Method to Make the Fracturing Decision: A Real Case Analysis from a Low Permeability Formation in Jungger Basin of China

摘要

Low permeability formation is the main exploration objective in China. Too much misjudgments of fracturing operation would tremendously increase the cost of exploration. We studied a method to estimate the well productivity for a Permian low permeability formation in Junggar Basin of China. Firstly, we made a statistical analysis to the lithology according to logging data and divided the lithology into 7 categories. We developed a set of standards to mark the seven categories. Secondly, we made a statistical analysis to 6 parameters of physical properties, such as porosity, permeability. We also developed a set of standards to mark the physical properties. Thirdly, we made a statistical analysis to DST data and divided the log-log curves of DST into 5 categories. We defined a pressure recovery rate that can reflect the formation energy status and analyzed the characteristics of the pressure recovery rate for different category DST curves. We marked the 5 categories DST curves and its pressure recovery rate. Fourthly, we made a mathematical statistics to the relationships of fracturing productivity with static and dynamic parameters, including pressure recovery rate, sand volume and fluid volume of fracturing. We obtained the productivity prediction equations by using multiple nonlinear regressions to static and dynamic parameters. Fifthly, we needed to use the method of the above 4 steps to mark the lithology, physical properties and DST of a new well and estimate productivity. Finally, we made a suggestion of fracturing to the new well. We applied the comprehensive formation evaluation method to 12 new wells of the Permian low permeability formation. Compared with the real oil-testing results after fracturing, the judgment accordance rate is 75%. The researched method can be generalized to other low permeability formation.