The Design And The Experimental Study On The Key Mechanisms Of The Wire-line Sampler For Gas Hydrate By Hole Bottom Freezing With External Cold Source

Natural gas hydrate is considered as the most promising new energy source because of its advantages of high energy density,cleanness,wide distribution and large reserves.Drilling sampling is the premise of evaluating hydrate reserves and exploitation,but the natural gas hydrate will decompose under normal temperature and pressure,and the conventional sampling technique can't meet the requirements of fidelity sampling.Pressure sampling technique use a ball valve sealing core cavity,set insulation measures,to maintain the original pressure and temperature of gas hydrate during sampling.The frequently-used pressure sample including PCB,FPC,PCS PTCS.Freezing sampling technology is based on the characteristics of temperature and pressure and characteristics of self-preservation effect of natural gas hydrate,proposed that freezing the hydrate core under hole to a temperature range(240K-271K)in which the hydrate can develop its self-preservation effect,and realize fidelity sampling.For the existing freezing sampler,the time for storage the cold source underground is too long,and the labor intensity is too big.In order to solve these technique problems,this paper proposed the design idea of the wire-line sampler for gas hydrate by hole bottom freezing with external cold source,which adopts the method of wireline coring technology,and send the cold source to the bottom of the hole using the fisher after the drilling stage.The wireline method can realize fast coring,and the method of cold source-external can solve the problem of long time underground cold storage.Considering the wireline coring method and the hole bottom freezing method,the structural design of the sampler is put forward.The overall structure design of the wire-line sampler for gas hydrate by hole bottom freezing with external cold source for was completed,the structure diagram was drawn,and the working principle of the sampler is analyzed.The composition and working principle of six regular mechanism s were analyzed,which include pneumatic cold source injection mechanism,finger mechanism,elastic card positioning mechanism,suspension mechanism,single action and buffering mechanism,regulating mechanism,and the importance of the key mechanisms were analyzed,which include seal cold storage mechanism,connecting mechanism and core freezing mechanism.First,completed the design of sealing connection mechanism,the structure can be divided into external cooling source module part and downhole tools part,the two parts are respectively arranged at the bottom of the cold storage mechanism and the top of the freezing mechanism.It can also be divided into three sub-mechanism according to the functions: playing card submechanism,salvage seal valve sub-mechanism and the lock sub-mechanism,respectively complete three functions for the connection process which include taking the downhole drilling,sealing the connection position,providing support force and lock the connected station.Completed the processing of the sealing connection mechanism prototype,tested the function of each sub-mechanism,proved that each sub-mechanism can achieve expected function.And the sealing connection mechanism can achieve the desired function after tested the whole sealing connection mechanism prototype.The test bench was built to measure the tension required for the connection of the sealing connection mechanism,and the requirements of the cold source external sampler for the tension of the winch were analyzed.Then,completed the design and analysis of the cold storage scheme of the cold storage mechanism,determined to use the alcohol as refrigerant,and mixed the liquid nitrogen with alcohol to prepare the low-temperature alcohol as cold source.The experiment show that the alcohol whose temperature is below its freezing point(-114 degrees)Still has good liquidity,these paper prepared cold source whose temperature is-130 K.Determined to take the ordinary cold insulation,and use the aerogel blanket as the cold preservation material for the cold storage chamber.Complete the structural design of the cold storage mechanism,analyzed the structure and working principle of the cold storage mechanism,and processing the experimental prototype and the test bench of the cold storage mechanism.Under the experimental conditions,the temperature of the alcohol will rise to-95? from-130 ? after 30min's storage.Drawed the temperature change curve of the cold source during the storage,the initial temperature of the cold source for the next frozen core experiment was confirmed.Finally,completed the design and analysis of the freezing methods of the frozen core mechanism,put forward the frozen core mechanism with "two segment" structure,whose advantages compared with the mechanism with the traditional three segment structure are less heat loss and better sealing performance.Put forward a new scheme that inject the cold source from the bottom of the freezing chamber,comparative analysis of the advantages of the new scheme with the old scheme which inject cold source from the upper of the freezing chamber,and find out the advantage of the new one is that it can realized the forced convection heat transfer between the cold source and the core,and ensure the uniform cooling of all the core.Combined with the characteristics of frozen core mechanism,determined to using PTFE as frozen cavity insulation materials.Completed the structure design of freezing mechanism,analyzed the structure and working principle of the freezing mechanism.Processed the prototype and the experimental equipment,and the core freezing mechanism was carried out experiment which identified that the core temperature rapid cooling,and core cooling under the uniform when inject the cold source from the bottom of the freezing chamber,the experiment show that the optimal injection pressure was between 0.30-0.50 MPa.