| The offshore oil exploitation is the key part of the world’s energy development,and it is also crucial for the"Energy Strategy"of China.However,the deepwater energy mining faces problems such as high pressure of water depth,large temperature difference with drilling depth,and high technical difficulty in offshore operations.Especially the domestic deepwater development wells have been in the exploratory stage,and almost no case can be followed in China.Among them,in deepwater drilling platform cementing operations,there is a section of spacer fluid between the cementing slurry and the drilling fluid,which will remain between the slurry and the seabed after being trapped.The trap spacer fluid will expand rapidly when heated during oil and gas production.When the pressure rises and exceed the strength of casing pipe,it will incur casing pipe expansion and damage,seriously affecting the safety of oil and gas production.In response to this problem and to protect the cementing casing,the thesis puts forward the idea of developing a spacer fluid system that can release internal pressure when the temperature rises.Around the idea,this thesis focuses on key contents regarding the design and preparation of compressible materials,the design and preparation of compressible spacer fluids,the optimization and evaluation of the compressible materials,and the application of compressible spacer fluid in practical engineering.The specific work includes:1.In this thesis,three technologies and material systems were designed,include high-temperature molten polymer wraps porous material to provide expansion space,release pressure from elastomer,and fixed-strength hollow particle material to limit pressure.When they were added into the trap spacer fluid,the pressure changes as temperature rises were investigated.The modified paraffin-coated porous material with a melting temperature of 63℃was selected as the pressure release material.Through the optimization of materials and coating process,the prepared polymer-coated porous material could significantly reduce the pressure in the closed casing after reaching the melting temperature,but the operating temperature range was narrow;the high-elastic mold tire powder was used as the pressure release material in the trial test,and the results show that the tire powder had a certain pressure-relieving effect,but the elasticity suffered significant reduction under the action of 20 MPa preload（actual working conditions）.Moreover,the release of pressure was limited as temperature rising;the use of a fixed strength hollow glass body could destroy the outer shell of the hollow closed-cell material at a certain temperature and pressure,which can provide new accommodation space.In this thesis,three systems including the modified paraffin-wrapped porous materials,the highly elastic tire powder and the hollow microbeads were used to optimize the combination.A high-temperature compressible material with adjustable temperature rise and pressure was developed,and the high-temperature compressible materials were added to the base spacer liquid.In the spacer fluid,when the temperature rose from 20 to 90℃,the trap pressure was lower than that of clean water by 34.38%and 27.5%lower than that of the commonly used spacer fluid;according to the calculation of volume change under equal temperature and pressure.The relief amount per unit volume of compressible spacer fluid was 0.33×10-3V,when the temperature of compressible spacer fluid rose from 20 to 90℃.The research results lay the theoretical foundation and material support for the temperature rise and pressure control of spacer fluid.2.In response to the requirements of deepwater cementing operations and production,the design performance requirements of spacer fluid were proposed;through research and selection of weighting agent,suspending agent and surfactant,combined with high-temperature compressible materials,the deepwater cementing spacer fluid technology be constructed.A comprehensive evaluation of their performance in the cementing pumping process temperature and pressure resistance,water loss,rheological properties,anti-pollution compatibility and heat-resistant casing pressure control and other properties was conducted,and then a compressible spacer fluid system suitable for deepwater cementing requirements was developed.The results show that:1)The compressible spacer fluid had good rheological compatibility with the water-based HEM drilling fluid for field operations,and the settlement stability was sound;2)The compressible spacer fluid had excellent rheological compatibility with cementing slurry,and the thickening and the compressive strength of composite material were virtually no affected;3)The density and basic properties of the compressible spacer fluid were almost unchanged after being cured by pumping high pressure of 42 MPa/50℃;4)The trap pressure of the compressible spacer liquid increased slowly and continuously with the increase in different heating rates of 0.5℃/min,1.5℃/min,2.5℃/min.The pressure increase value at 90℃was controlled below 20 MPa,which was lower than the maximum pressure value at which the casing was damaged;5)with the operation of different starting pressure from20 to 35 MPa,the trap pressure of the compressible spacer continuously increased to about 45to 51 MPa.When the temperature dropped down to room temperature,the pressure of the trap spacer also decreased.When the temperature dropped down to 20℃,the pressure was reduced to 19～27 MPa,only 1～8 MPa negative pressure,they also can ensure the integrity of the spacer fluid;6)The pressure rise curve and the pressure drop curve basically coincided after 8 cycles of heating and cooling,indicating that the compressible spacer exhibited excellent working performance of repeated temperature rise.The experimental results provided safeguard for the application of spacer fluid in actual engineering.3.Combining the working conditions of the cementing operation in Lingshui block at the South China Sea,the high-temperature compressible materials produced in the pilot production and the conventional spacer fluid materials on site were used to optimize the design.The compressible spacer fluid construction with a density of 1.65 g/cm3 Formula（100%Freshwater+1%Suspending agent+20%Surfactants+40%High temperature compressible material+190%Barite）was obtained.The field test results showed that:1)The viscosity of the spacer fluid funnel was 113 s,and the water loss was 125 m L in 30 min.It had sound compatibility with the pollution experiment of cementing slurry and drilling fluid,and met the requirements of construction operations.2)Under the actual working conditions starting at 4℃and 16 MPa pre-compression,the compressiblespacer fluid trapped was pressurized to 7.1 MPa at 52℃,pressurized to 13.8 MPa at 75℃,and pressurized to 22 MPa at 90℃,when the temperature dropped,it decreased by 3 MPa,4 MPa and 6 MPa respectively,effectively protecting the casing from damage or collapse.3)In situ application of the compressible spacer fluid in the Lingshui25-1E-1 well,there were no abnormal conditions such as pump jam or pump stop during the cementing process,remotely operated vehicle observation of subsea wellhead without casing pressure,and no casing expansion or collapse phenomenon in the later production.Phenomenon,this work laid a practical foundation for the popularization and application of the compressible spacer fluid system in deepwater cementing. |
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