Research On Thermal Insulation Structure Of Heavy Oil Cold Production Wellbore

In recent years,the demand for crude oil in China continues to rise,but the viscosity of rich heavy oil resources increases sharply due to the temperature drop in the wellbore during the lifting process,so it is difficult to lift the crude oil to the surface relying on the formation energy.Wellbore thermal insulation technology can improve wellbore temperature,reduce the flow resistance of heavy oil in wellbore,and it does not need additional agents and additional energy.It is a low-cost heavy oil production method,which can solve the problem of limited production due to high energy consumption.The establishment of high-precision wellbore model can accurately guide the construction of wellbore thermal insulation structure.Therefore,this paper complements and perfects the previous models,establishes a high-precision wellbore temperature-pressure coupling model of heavy oil cold production considering thermal physical properties of formation to study wellbore thermal insulation structure,discusses the influence of thermal insulation material laying position on thermal insulation effect,and combines the calculation results of the model with the initial investment calculation expression to obtain a wellbore thermal insulation structure that can meet the thermal insulation requirements and is the most economical.The main work and conclusion are as follows:(1)The research status of wellbore thermal insulation structure and thermal insulation materials was extensively investigated.The advantages,disadvantages and the application conditions of the internal and external wellbore thermal insulation and vacuum thermal insulation tubing were compared.Finally,the wellbore external thermal insulation structure suitable for example well was finally selected.Through literature and factory investigation,nine kinds of thermal insulation materials,such as aerogel felt,microporous calcium silicate,titanium ceramic insulation board,aluminum silicate fiber blanket,plate aerogel,NT-260 aerogel coating,NT-700 aerogel coating,RLHY-12/150 thermal insulation coating and ZS thermal insulation coating,were preliminarily screened.Their compressive strength,as well as the density,thermal conductivity and hydrophobic rate before and after compression were tested.The test results showed that only aerogel coatings and RLHY-12/150 thermal insulation coatings had passed the compressive strength test.Aerogel profiles and nano-ceramic coatings were expensive,and the aerogel coating had excellent thermal insulation performance.Finally,the NT-260 aerogel coating was selected above and below the moving liquid level to construct the thermal insulation structure of the example well,according to the difference between the annular media above and below the moving liquid surface.(2)The energy conservation,momentum conservation and mass conservation equations of wellbore considering friction heat generation and formation thermal physical properties were established.The establishment process of solving the equation of wellbore total heat transfer coefficient,which is the key parameter of wellbore steady heat transfer,and the establishment process of solving the equation of dimensionless temperature,which is the key parameter of formation unsteady heat transfer,were described in detail.The expressions for calculating the physical parameters of tubing and annulus fluid,as well as the outer wall temperature of insulation layer,the inner wall temperature of casing and the temperature at the interface between cement ring and formation required to calculate the total heat transfer coefficient of wellbore were given.The iterative solution process of the wellbore high-precision temperature-pressure coupling model was described in detail,and the relationship between formation volume specific heat capacity and formation thermal conductivity with formation depth was fitted.(3)A high-precision temperature-pressure coupling model of a sample well was established.In the VS software,C language was used to compile the wellbore model solving program,and the accuracy of the model was verified with the relevant oil production data before the thermal insulation.It was found that neglecting the spatial distribution of thermal physical properties of the formation would lead to the actual wellhead temperature lower than the design requirements.The insulation material should be laid down from the wellhead to meet the insulation requirements,and the calculated laying thickness was the only thickness corresponding to the laying length.With the extension of well opening time,the wellhead oil production temperature gradually increased and then tended to be stable.Through the program calculation,the aerogel coating 10.65 mm with a thermal conductivity of0.0246W/(m·K)at 82°C was coated from the wellhead to 2750 m on the outer wall of the tubing,which can meet the design requirements of the thermal insulation structure to increase the oil output temperature of the example well by 20?.Summarizes the design idea of wellbore thermal insulation structure: determine the requirements of wellbore transformation based on the understanding of the basic working conditions of oil wells,optimize the thermal insulation structure and materials according to certain principles,and determine the design scheme of thermal insulation structure combined with the initial investment calculation.