| Volume fracturing is one of the key technology in tight oil development,the research was mainly based on the conventional reservoir fracturing theory.There were less experimental measurement results on the mechanical properties of tight oil reservoir parameters accurately,complex artificial fracture formation mechanism and methods was unclear,which can not be better to realize the fracturing theory calculation,quantitative prediction and design.Therefore,it is necessary to study mechanics properties of tight oil reservoir rock,volume fracturing fractures extension rules and mechanism of complex fracture network,which will be great significance for achieving the success volume fracturing reconstruction and commercial exploitation of tight reservoir.In this paper,the Fuyu tight oil reservoir in south Changyuan of daqing was taken as the research object.The forming mechanism and extension rules of fracturing fractures were studied by using the indoor test,theoretical analysis and numerical simulation.The tight sandstone samples are characterized by high strength and high hardness in mechanics,so the rock mechanics experiments were done by high temperature-pressure of triaxial apparatus,in which the mechanics parameters characteristics were evaluated.The properties of tight sandstone mechanics are deeply affected by buried depth,and the compressive strength and elastic modulus increase with confining pressure,the variation trend of stress-strain curve from different sampling direction is similar.Considering the rock deformation in the process of volume fracturing is complicated,brittleness evaluation index was established to reflect the tight sandstone breaking process overall based on the the rock fracture energy evolution.Using the brittleness index with well logging data and analysis of the brittleness mineral content,the fracturing ability of tight sandstone could be evaluated comprehensivily.The study showed that fractures network could be formed in sandstone samples tesded in this paper,which provided the basis for the fracture network formtion study.Compared with shale and coal rock,there is no bedding,cutting and more natural fracture in the tight sandstone of Fuyu oil reservoir,the stress release crack formation mechanics model was established,the induced fractures formation conditions,extending direction and extension condition were studied under the action of induced stress,the complex fracture network formation mechanism of the tight sandstone was confirmed under the condition of natural fracture is low-development.Then the interaction bettween natural fracture and the hydraulic fracture was analyzed under different conditions.The discriminant model of hydraulic fracture shearing along natural fractures was established,influence of the interaction between hydraulic fracture and natural fracture by in-situ stress,approaching angle and fracture characteristics was studied.Based on the above research,the main control factors of fracture network formation of tight oil reservoir was mastered,the numerical model of volume fracturing induced stress was built.Then the effect on volume fracture stress distribution was studied,such as fracture spacing,natural fracture length and fracture reservoir properties,etc.Finally,based on above research,the principles and construction methods of effective volume fracture information were put forward.Combined with practical engineering factors,the process design and control methods of improving the degree of the fracture network formation were studied considering the working fluid properties,injection rate and horizontal fracture spacing.The field application was satisfactory,which was proved that the fracture network can be formed by the control methods proposed in this paper.This research results could also be used in similar tight reservoirs and other unconventional reservoirs. |
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