Research On Water-based Drilling Fluid Technology Of Shale Gas Well

Shale gas reservoirs are unconventional gas reservoirs with large reserves,low permeability and high clay mineral content.The total shale gas reserves within 3500meters of the Zhongmu block in Henan Province are 21,449 million cubic meters,and the technical recoverable reserves are 12.75 billion cubic meters,which has good commercial development potential.In the process of drilling on shale gas formations,it is easy to cause instability of the borehole wall.At the same time,the friction of the horizontal well section is relatively large,and the performance of the drilling fluid is restricted,plugging,and lubricating.It is difficult to meet the requirements of conventional water-based drilling fluids.The need for drilling safety in shale gas formations.Oil-based drilling fluids are widely used in the drilling of shale gas formations,but they have problems such as environmental pollution,poor cementing quality,and high cost.Therefore,this paper conducts research on shale gas water-based drilling fluid technology in the Zhongmu block.Based on the analysis of the complex situation of drilling in the Zhongmu block and the physical and chemical properties of mud shale,this paper studies the instability mechanism of the borehole in the Zhongmu block.The instability mechanism of borehole is mainly:(1)Mud sheet in the Zhongmu block.There are crisscross micro-cracks on the rock surface,and the drilling fluid filtrate can easily penetrate the shale shale along the micro-cracks,causing the mud shale to collapse and fall off.(2)The mud shale clay mineral content in the Zhongmu block is relatively high,and the clay mineral water,the expansion of mud shale caused by chemical expansion causes uneven opening of micro-fractures and invasion of filtrate;(3)the formation of coal seams in Shanxi Formation-Taiyuan Formation in Zhongmu Block,with large Young's modulus of coal rocks,low fracture pressure,and cleavage as well as micro-fractures develop,while clay minerals are trapped in the fractures of coal rocks,the hydration and expansion of clay minerals caused by the infiltration of drilling fluid filtrate results in uneven stress on the coal rocks,causing coal rocks to collapse and collapse.Based on the analysis of the instability mechanism of the borehole wall in the Zhongmu block,the corresponding drilling fluid technical countermeasures are proposed.The countermeasures are:(1)It has good inhibitory property;(2)It has good plugging property;(3)It has good fluid loss property;(4)Reasonable drilling fluid density.The inhibitor amine silanol HAS and its addition amount were optimized through the hot roll recovery and high temperature and high pressure expansion experiments.The nanometer micelle plugging agent ASM,micron-level wall-fixing agent AGM,warm-pressing film-forming plugging agent ACM,and other blocking agents and their additions.The free water complexing agent LKY and its additions are optimized by the free water content measurement experiment.The lubricant LUBE and its dosage were optimized through the friction coefficient determination experiment.On this basis,a water-based drilling fluid system capable of meeting the safety requirements of shale gas formation drilling in the Zhongmu block was constructed.Its formula is:3%bentonite slurry+0.2%Na OH+0.3%LV-PAC+1%LKY+1.5%filtrate reducer+1%HAS+2%ASM+3%AGW+2%ACM+2%LUBE+3%KCl,aggravated by barite.Based on the evaluation of the performance of the shale gas water-based drilling fluid system in the Zhongmu block at different densities,the performance of inhibition,plugging performance,lubrication performance,anti-pollution performance,free water restraint performance and reservoir protection effect were evaluated.The research results show that the constructed shale gas water-based drilling fluid system in the Zhongmu block has good performance when the density is 1.05 to 1.25 g/cm~3,and the temperature resistance can reach 120?.The system has good suppression performance,lubrication performance,plugging performance,anti-pollution performance,free water restraint performance and reservoir protection effect.