Research On Synthetic Drilling Fluid Technology For Offshore Complicated Strata In West Africa

With the increasing demands for oil and gas,oil exploration and development has expanded to the ocean,and 70%oil and gas resources have been discovered in deep water in recent years.West Africa is rich in offshore oil and gas resources and has become a major region for oil and gas exploration and development.Taking the geological conditions of Nigeria and Cameroon as typical research objects,it is found that due to the complex geological conditions,the formation is loose,prone to hydration,the pressure system is complex,and the safe density window is very narrow,and the downhole is prone to leakage and serious reservoir damageproblem.There is an urgent need for a drilling fluid with strong inhibition,good lubricity and environmental protection to reduce wellhole complexity,so the environmentally friendly synthetic-based drilling fluid is the first choice.Four treatments for synthetic-based drilling fluids were synthesized in this paper.Aiming to solve the sedimentation of the synthetic-based drilling fluid system under high temperature,a high-temperature-resistant rheology modifier was synthesized by fatty acid and polyol amine,forming a space network structure which has the gel properties by interacting with the emulsifier in the interface.The performance evaluation results show that the dynamic shear force of the drilling fluid can be effectively improved without affecting the apparent viscosity and plastic viscosity,thereby improving the settlement stability under high temperature.The main emulsifier is synthesized with fatty acid and modified polyamine,and the auxiliary emulsifier is synthesized with tall oil rosin and polyol.The emulsification efficiency and thermal stability are greatly improved by adding more hydrophilic groups of a single emulsifier molecule.The performance evaluation found that 4%main emulsifier and 4%auxiliary emulsifier could maintain the demulsification voltage over 581V after aging at 220℃for 16h,and meant excellent high temperature resistance.A high temperature resistance fluid loss reducer with good dispersibility was synthesized by aminocarbonylation on lignite,and the filtration loss was less than 3.0m L under high temperature and high pressure.A leakage prevention and plugging technology was formed by using polyester fiber plugging material,100-mesh superfine calcium carbonate and LTECH plugging material,which effectively improves the pressure bearing capacity of the formation on the basis of effectively plugging pore.A synthetic-based drilling fluid suitable for offshore West Africa has been constructed by the synthesized agents as the core,which has adjustable density of1.5-2.0g/cm³,excellent sedimentation stability and reservoir protection,and Low toxicity.A high-temperature and high-pressure sedimentation stability evaluation instrument that can simulate downhole temperature and pressure was fabricated.Through the analysis of high-temperature and high-pressure rheology and sedimentation stability.The coefficient between the dynamic shear force of the drilling fluid and the sedimentation coefficient SF is high,and the sedimentation stability of the drilling fluid is improved by increasing the dynamic shear force under high temperature.The permeability recovery values of the cores before and after aging reached 88.66%and91.07%,respectively.The EC₅₀ is 42817 mg/kg,seed germination rate increased from8.67%to 44.7%.The synthetic-based drilling fluid in this paper was successfully applied in the field of Fox Z Well,which solved the problems of weighting sedimentation on-site,high viscosity and shear force of drilling fluid and poor leakage prevention and plugging effect.Finally,the drilling was successfully completed.The application of drilling fluid in West African offshore laid the foundation and broaden the prospects for promotion and application.