Risk Analysis And Evaluation Of Fracturing Operation In Horizontal Shale-gas Well

With the continuous development of economy and society,the demand for energy is increasing.Shale gas,as an important part of non-conventional energy,has been paid great attention by the domestic society in recent years.The fracturing technology in horizontal well,as a vital technical means of shale-gas production,has been widely used in the field of shale-gas development.As it is a very complicated process,which requires large area and scale of constant drilling.It is necessary to carry out risk analysis and evaluation due to the likely serious consequences.For the healthy safety and environmental problems aiming at fracturing process in horizontal shale-gas well,in this paper,we identify the risks based on the theory of Accident Chain and build an AHP model regarding pipe sticking as the target layer.The main factors are divided into four categories.We combine weighted analysis and expert evaluating method by fuzzy comprehensive judgment to form a quantitative system in risk profile of pipe sticking.In this paper,a model of fault tree analysis is built considering the fault of pulling drill as a top event to analyze and evaluate risks more specifically.There are 81 minimal cut sets by qualitative analysis indicating that the event is very dangerous.For the uncertainty of fracturing process in horizontal well,we apply to the method of triangular fuzzy numbers to calculate the fuzzy probability of the top event.And the general fuzzy risk level is optimized,determining the system in a safe state.It can be seen from the ranking of importance degree of fuzzy probability that the management defects,poor safety awareness and lack of experience are the main factors in the occurrence of the accident.Therefore,the most important is to strengthen the management and safety training,controlling the human error probability.Besides,as an indispensable element in the fracturing process,the fracturing fluid plays an important role in the control of the accident.At last,we chart control measures according to the research conclusion and the actual situation of fracturing operation in shale-gas horizontal well,which lays a foundation for the management of the safety in the fracturing process.