Study On Steam Dryness Test Method And Sensor Design Of Injection Well

With the continuous decline of China's conventional oil reserves and production,the status of heavy oil has become increasingly prominent.However,due to the high viscosity and high density of heavy oil,it is extremely difficult to explore and convert it into actual resources.At present,for exploring heavy oil,the main method is the heavy oil thermal recovery technique,which is to inject high-temperature and high-pressure steam into the steam injection well.And then,because the steam contains large amount of heat which can be used to increase the temperature of the oil layer to reduce the viscosity of the heavy oil,and to reduce the resistance of the fluid layer.Consequently,conventional oil exploration and production methods can be used to explore the heavy oil.Obviously,in order to effectively improve the recovery rate and to save energy consumption,we have to accurately acquire the information about the position and distribution of the oil layer,and to clarify the absorption of injected steam in each part of the oil layer.Therefore,the steam dryness,one of the most important parameter of the steam thermal efficiency characteristics should be accurately measured on-line.Based on the understanding of the physical properties of water and steam,this paper researches the corresponding relationship between the dielectric constant and the refractive index of saturated water/steam and the dryness under certain temperature and pressure conditions.With these formulated relationships,two dryness inversion models were constructed.Firstly,a refractive index sensing structure based on the photonic crystal fiber surface plasmon resonance(PCF-SPR)was designed,and the sensitivity of the refractive index measurement was simulated and analyzed.And the feasibility of the inversion model was theoretically confirmed.Secondly,the error analysis of the capacitance based dryness measurement model is carried out.Based on this analysis,a multi-layer cylindrical capacitance sensing structure is proposed to measure the steam dryness.Consequently,the multi-layer capacitance based steam dryness sensor is designed for field test,which can be employed for accurately measuring the steam dryness of steam injection wells.For the physical properties of saturated water and steam,the characteristics of parameters such as viscosity,specific volume,dielectric constant,and compression coefficient of steam at different temperatures and pressures were analyzed.In addition,the effects of steam injection intensity and speed on steam dryness were analyzed too.With these analyzing results,the relationship between steam dryness with temperature,pressure,dielectric constant and refractive index was studied in detail.As a result,the accurate relationships between steam dryness and the corresponding density and relative dielectric were revealed,which can provide stable theoretical support for the refractive index and capacitance based steam dryness measurement models.A theoretical model for dryness measurement based on the corresponding dielectric constant was constructed.Based on this model,detailed analysis on the influence of the plate structure of capacitive senor to the performance of the capacitance based method.Therefore,a multilayer cylindrical capacitor structure was proposed.Based on the physical parameters and distribution characteristics of the medium to be measured,the theoretical measurement error of the structure is analyzed.And the constant factor k of the theoretical dryness measurement model was confirmed to be 1/2.When the temperature error is 0.1 ° C and k = 1/2,the corresponding measurement error of dryness is less than 4%.At the same time,the corresponding relationship between steam dryness and the corresponding refractive index was obtained by simulation.Therefore,by employing PCF-SPR technology to measure the refractive index,a novel large-channel Ag film PCF-SPR sensor structure was designed with a refractive index resolution of 1.538 10-5 RIU.Based on the dielectric constant based steam dryness inversion model and the designed multilayer cylindrical capacitance sensing structure,a steam dryness measurement system for steam injection wells was designed and manufactured.Considering the under-pressure capability and the sealing process of the sensor,a four-layer cylindrical capacitor structure is employed to improve the test accuracy.For accurately measuring the capacitance value of the employed capacitance sensor,the corresponding precise capability measuring circuits were studied in-depth.Specifically,comparative analysis of the advantages and disadvantages of the dual harmonic wave based method,the direct measuring method based capacitor chip and the frequency based measuring method was conducted.In order to ensure the stability and the consistency of the proposed system,tri-time frequency measurement method was proposed to accurately measure the object capacitance by efficiently filtering out the disturbances caused by stray capacitance and electromagnetic interference.Therefore,the measuring and sampling circuits were designed.In addition,the corresponding host computer software was programed to analyze the measuring data.The final capacitance measuring accuracy can achieved to 0.01 p F.Finally,for the proposed dryness measuring system,indoor experiments and data analysis were conducted to calibrate the designed capacitance sensor to the temperature and pressure.In addition,field tests were conducted for steam injection wells Qi-40-22-K36,Jin-99,and Du-H5 in the Liaohe oilfield.Experimental results illustrated that the steam dryness of the tested steam injection wells was vary within the range of 0.5 to 0.6,which is consistent with the measurement results of manual sampling method.Moreover,the corresponding testing error is under 5%.Obviously,the proposed method is an ideal solution for the on-line dryness measurement for the steam injection wells.