Plugging Technology Research For Preventing Gas Invation Of Fractured Gas Reservoirs In The Upper Part Of Yingshan Formation In Shunnan Area

The fracture and porosity of the upper Ordovician Yingshan Formation reservoir in Shunnan area are well developed and the distribution law is complex.It is a typical high temperature and high pressure carbonate fractured reservoir.The operation data of Yingshan section in Shunnan block show that gas invasion is easy to occur during drilling,oil and gas channeling is fast,gas invasion is difficult to be stabilized by increasing drilling fluid density.During the period of drilling and completion,the total hydrocarbon value of the drilling fluid increases after a long period of quiescence.In order to ensure the safety of well control,frequent circulation and exhaust operations are needed,leading the long drilling cycle,low drilling efficiency,and the well control safety is threatened.Therefore,it is necessary to study the leakage and gas invasion of the reservoir and find out the reasonable countermeasures to realize the high efficiency and safety drilling of the upper Yingshan Formation reservoir in Shunnan.In this paper,the law of leakage and gas invasion in the drilling process of the upper Yingshan Formation reservoir in Shunnan area is studied,and the while-drilling plugging evaluation of fractures of different scales is carried out in combination with experiments.A set of safe,effective and wide-adaptable gas plugging technology is formed,which is of great significance to the well-control safety of fractured reservoirs.Through research,the main results obtained are as follows:1)The geological and reservoir characteristics of Shunnan Block are analyzed,and the characteristics of gas invasion and leakage in the drilling process are determined based on the drilled data:frequent gas invasion and serious gas leakage,both of them coexist;2)By judging the type of leakage and gas invasion,the corresponding mathematical model is established to simulate the stage from leakage to gas invasion,and the influencing factors are analyzed,and the indoor experiment is carried out to simulate the law of drilling fluid leakage in the well.3)Simulating formation conditions,adopting high-temperature nano-micron and film-forming materials to conduct LWD plugging technology,plugging micro-fractures and pores while drilling,forming LWD plugging technology suitable for drilling site construction in Yingshan Formation.According to the given technology of fracture closure,the plugging scheme of the well is formulated according to the working conditions of a specific well.The results show that the gas invasion mechanism of the reservoir belongs to the gas invasion caused by leakage,that is,the gas overflows into the wellbore when the drilling fluid enters the compressed fracture space of the formation;the larger the fracture space(the width,the height and the length of the fracture),the bigger the viscosity of the drilling fluid and the bigger the pressure difference,the longer the gas invasion time will take.For different opening cracks,different plugging formulations are used for plugging.