Experiments Research Of Degradable Cement For Medium-temperature Geothermal Well

The exploration and utilization of geothermal energy has received more attention around the world.In General,the geothermal energy is divided into shallow geothermal energy,hydrothermal geothermal energy and enhanced geothermal systems?EGS?,according to thermal fluid transfer mode,temperature range,as well as the way of utilization.EGS is mainly utilized for generating power through extracting thermal energy of hot dry rock in the depths of the earths crust.On the one hand,the cracks will lead to lost circulation during EGS drilling process,if the leakage formation is reservoir,the plugging operation cannot reduce the permeability of the reservoir and impede the flow of the fluid;On the other hand,fracturing is one of the key technologies of EGS exploitation,and multilayer fracturing can greatly reduce EGS development cost,multilayer fracturing also need temporary plugging technology.We can use the temporary plugging material to seal the first crack and then stimulate the second even the third crack.The temporary plugging material can degrade after the stimulation is completed.For conventional hydrothermal geothermal resources,lost circulation is more frequent and severe,if the leakage formation is reservoir,using temporary plugging materials for sealing is also important.Suguma has started experiment researches of degradable cement for EGS reservoir which exceeds 200?.Polymer degrades and releases gas under such high temperature,damaging the compact structure and strength of the cement.Through literature research,chemical foaming agent more often used in the preparation of porous materials can decompose and release gases under certain temperature,and different chemical foaming agents have different decomposition temperature and different gas evolutions.For example,the decomposition temperature of AIBN,NaHCO₃ and OBSH is respectively 90¹10?,100¹50?,140¹60?.This article starts the experiment researches of degradable cement for medium temperature geothermal wells?90¹50??.The objective is to design three cement formulas using three kinds of chemical blowing agents such as AIBN,making cement degrade at 90?,120?,150?.During the experiment,we first analyze the decomposition properties of the three foaming agent in the air,obtaining their beginning decomposition temperatures and maximum decomposition temperatures;And then,we research the decomposition properties of single foaming agent and compound agents in cement.We design several groups of cement formula and obtain three kinds of degradable cement formulas,that is 90?:P.O.42.5 cement+6%AIBN,120?:API class G cement+0.5%NaHCO₃+0.5%OBSH,150?:API class G cement+0.4%AIBN+0.4%NaHCO₃+0.4%OBSH,by testing cement's compressive strength and permeability coefficient.Finally,we compare the permeability coefficient of degraded cement with the permeability coefficient?permeability?of the reservoirs greatly utilized in Beijing?Tianjin areas.Besides,we make comprehensive evaluation on degradable cement's properties,the experiment results show that the three degradable cement formulas have good performances of fluidity,setting time,sedimentary stability,compressive strength and permeability,and they can meet the temporary plugging requirements for medium temperature geothermal well.