Study On Cementing Slurry Properties With Persistent Sealing Ability In Long Open Hole

As the scale of oil and gas exploitation increases and the difficulty of drilling and production technology increases,the number of ultra-deep wells and complex wells increases continuously,the development of cementing technology in marine wells in Western Sichuan faces a technical problem-how to improve the cementing quality of 193.7 mm production tailpipe and 139.7 mm reservoir tailpipe,ensure wellbore integrity and reduce safety accidents.In 193.7mm tailpipe production,the length of cementing casing is long,and the length of open hole is over 3000m.There are great differences between upper and lower formation performance.In the process of drilling,high drilling fluid density is needed for balanced well pressure in marine formation.Because of complex reservoir conditions and active formation fluids,wellbore fluids are always in dynamic state:either overflow or leakage,or gas-liquid interaction replacement to achieve dynamic equilibrium.The poor borehole geometry and drilling fluid performance of 139.7mm oil reservoir tailpipe during drilling result in low displacement efficiency and poor cementing quality of cement slurry,and gas channeling due to poor performance of cement slurry such as water loss and stability during cementing.The uneven density of cement slurry and insufficient mixing energy result in poor strength development of cement paste.The change of temperature and pressure caused by fresh water replacing slurry and fracturing in later stage causes the failure of annular hydraulic seal.The above points have become the main factors affecting the long-term sealing ability of long-open-hole cement slurry.This requires adjusting the performance of the pre-fluid-cement slurry,ensuring the formation stabilization,improving the displacement performance of the pre-fluid-cement slurry,enhancing the long-term sealing capacity of cement paste,in order to ensure the cementing quality.Therefore,it is necessary to establish a comprehensive evaluation method of isolation fluid performance,cement slurry performance and long-term sealing capacity of cement sheath,and to optimize the formulation of isolation fluid and cement slurry system with the above evaluation methods,so as to select efficient isolation fluid system,large temperature difference cement slurry system and cement slurry with long-term sealing capacity System.Aiming at the drilling situation in Longmen mountain area of Western Sichuan and the technical difficulties of cementing in Sankai and Sikai reservoirs,this paper designs the pre-cementing fluid and cement slurry system.In the aspect of pre-cementing fluid,this paper uses different dosage of flushing agent to evaluate the difference of wetting effect and uses six-speed rotary viscometer to carry out the pre-flushing efficiency.In the experiment,the formula of the pre-flushing liquid is optimized after the data are obtained,and the flushing time and the construction displacement are calculated to provide the data support for the field construction.The flushing efficiency evaluation experiment is conducted to explore the best way to scour this type of oil-based drilling fluid.In the aspect of cement slurry system,starting from low density,conventional density and high density cement slurry,aiming at the problem of super retardation and high bottom hole temperature in the middle and long sealing section of deep and ultra-deep wells due to the low upper temperature of the sealing section,the material type and dosage are optimized,and the suitable Longmen is selected.Cement slurry formulation required for cementing in mountainous areas is systematically evaluated to meet the requirements of cementing design.At the same time,the cement slurry system of tail pipe in oil reservoir is further studied,and a set of cement slurry system suitable for narrow gap and long-term sealing ability of tail pipe in oil reservoir is selected.The sealing effect of cement ring is evaluated.The nano-liquid silicon elastic anti-gas channeling agent is selected to make full use of thixotropy and retardation of liquid silicon to prevent gas erosion.The advantages of nano-liquid silicon anti-channeling agent and latex anti-channeling agent are integrated to form a high-temperature reinforced anti-channeling cement slurry system.Field application shows that the cement slurry can not only play a good role in preventing gas channeling in the process of cementing and completion,but also greatly improve the long-term sealing capacity of the later cement ring.