Scheme Optimization Of Horizontal Well Exploitation In The Shenhu Sea Area Hydrate Reservoirs By Depressurization

China's Shenhu sea area has a huge amount of natural gas hydrate resources.The results of the second round of hydrate trial production in this sea area in 2020 show that horizontal well exploitation can greatly improve the productivity of natural gas hydrate reservoirs.The previous research work on the exploitation of hydrate reservoirs in Shenhu sea area mostly focused on short-term or long-term production behavior,and lack of research on engineering application.Therefore,carrying out the scheme optimization of horizontal well exploitation in this sea area hydrate reservoirs by depressurization is of great significance to promote hydrate industrialization and ensure national energy security.The exploitation of natural gas hydrate involves complex porous flow process,and its numerical simulation technology is extremely challenging.At present,several international well-known numerical simulation software for natural gas hydrate production have their own advantages and disadvantages.This thesis selects the widely used numerical simulation software to carry out adaptability analysis.In view of the lack of detailed data on depressurization,gas and water production in the open trial production data of Shenhu sea area,this thesis was based on the geological and logging data of the trial production well AT1-P in the Eastern Nankai Trough of Japan in 2013,uses the selected software to carry out historical fitting of the field gas and water production data of the well,by compares the fitting results,The numerical simulation software with high adaptability and reliability was selected as the research software.On this basis,based on the geological and logging data of SHSC-4 well in Shenhu sea area,and the scheme optimization of horizontal well exploitation were carried out.The main work contents includes the optimization of horizontal section layout location and length,and the production scheme.The following understandings have been obtained:(1)Compared with CMG-STARS,TOUGH+HYDRATE has better adaptability in hydrate productivity evaluation.(2)However,when the horizontal section is arranged in hydrate layer II,due to the large production pressure drop(3MPa),the gas throttling expansion effect causes the formation of high saturation hydrate in the wellbore,resulting in a sharp decline in gas production rate in the later stage.(3)When the horizontal section is arranged in hydrate layer II,small-pressure drop(1MPa)depressurization production,the longer the horizontal section length,the better the production capacity.However,with the increase of the length of the horizontal section,the average cumulative gas production increment per meter is gradually decreasing,especially when it increases from 260 m to 300 m,the water and gas production rate begin to be significantly affected by the secondary hydrate.Therefore,300 m is a more reasonable length of the horizontal section when exploiting the hydrate layer II.(4)When the horizontal section is arranged in hydrate layer II,without heating,the secondary hydrate formed at the root of the wellbore and near the well due to throttling expansion effect is the main factor limiting the productivity during high-pressure drop production.the combination of depressurization and heating production can eliminate and prevent the formation of secondary hydrate in the wellbore and the reservoir around the well.The simulation results show that heating has a good effect on eliminating and preventing the formation of secondary hydrate.When the production pressure drop increases step by step after heating,the cumulative gas production is greatly improved compared with that without heating.In this thesis,the horizontal section layout location and length,and the production scheme of horizontal well exploitation in the Shenhu sea area hydrate reservoirs by depressurization were optimized.The research results can provide theoretical guidance for the efficient exploitation of hydrate reservoir in this sea area,and provide useful reference for the development of hydrate reservoir in other sea areas.