Simulation Research On Cementation Characteristics In Cementing Of Gas Hydrate Formation In South China Sea

At present,there are huge reserves of natural gas hydrate resources in South China Sea,and the construction of wells,to extract marine gas hydrates is still the main method,especially the horizontal wells.Cementing is an important method for constructing wellbore and ensuring the smooth implementation of reservoir reconstruction such as subsequent fracturing.The quality of cementing has an impact on hydrate reservoirs.The safe construction of wellbore and trial production to increase production and stabilize production are essential.However,the formation of natural gas hydrate is soft and difficult to form effective cementation with cement,which is not conducive to the depressurization of natural gas hydrate and fracturing.At present,the development law of cementation strength,formation temperature field and stress field of hydrate formation It is difficult to guide cement slurry performance design and cementing quality due to the unclear understanding of the changing law of the cement ring and the influencing factors of the integrity of the second interface.It is necessary to conduct in-depth research on the cementing of the gas hydrate formation in the South China Sea and the second interface formed after cementing.To provide technical support for the cementing of natural gas hydrate formations in my country’s seas.By preparing gas hydrate simulation formation,designing and processing a gas hydrate simulation formation cementing two interface cementation strength test device,the influence of cement slurry system,formation type,curing time,etc.on the cementing strength of the two hydrate simulation formation cementing interface is evaluated.The change rule of the bonding strength of the two interfaces is clarified.Adopting the bonding contact to simulate the cementation of the two interfaces,a finite element analysis model for the cementing process of horizontal wells in gas hydrate formations was established,and the gas hydrate formation temperature,changes in ground stress and cementing were analyzed during the drilling,cement slurry,and hardening stages.The law of interface damage reveals the influence of cementing process on the quality of natural gas hydrate formation and the bonding quality of the two interfaces,and provides guidance for the design of cement slurry system and cement stone performance.The research results show that:(1)The short-term cementation strength of the second interface of natural gas hydrate simulation formation cementing is low.The cementation strength at 1 d is 0.606 MPa,which is about 1/4 of that of sandstone formation,and it is 1/5when using low-density cement slurry;The bonding strength of the second interface increases fastest at 3 days,up to 91.6%,and increases slowly after 5 days.The size of the bonding strength is closely related to the development speed of the compressive strength of the cement stone.(2)Analysis of the cementing and test production process found that: bottom hole static temperature,hydrate layer drilling fluid circulation time,cement slurry heat release,mining method,etc.mainly affect the formation temperature field,and have little effect on the bonding of the two interfaces,and phase change The ability of endothermic materials to reduce the heat of hydration of cement is stronger than that of fly ash,and it has a smaller range of influence on the temperature change of the hydrate formation.(3)The damage simulation study on the second interface of cementing shows that at low temperature,the early strength of cement slurry develops slowly,the cementation strength of the second interface is also low,and the second interface is easily damaged.Therefore,hydrate cementing cement slurry should have good early strength at low temperature.Characteristics: The higher the cement elastic modulus,the greater the cement stress,the smaller the damage criterion of the cementing interface,and the safer the interface.It is necessary to optimize the cement elastic modulus according to the cement ring stress and the damage process of the cementing interface to ensure the effect of cementing and packing.