Study On Coalbed Methane Micro-foam Drilling Fluid Based On Nanomaterials

There are many coalbed methane basins in eastern Yunnan province.The Enhong block is an important coalbed methane resource area in eastern Yunnan.The proved reserves of coalbed methane are sufficient,which has good development prospects.The mineral composition,microstructural characteristics and physicochemical properties of the coal seams and the roof and floor of the coal seam in Enhong block are analyzed by experiments.The experimental results show that the micro-fractures in the coal seam of Enhong block are developed,and the content of clay minerals in the roof and floor of the coal seam is relatively high,and it is easy to occur complex accidents such as hydration expansion and borehole instability,which is not conducive to the efficient development of coalbed methane.In view of the above problems,through analyzing the characteristics of coalbed methane drilling fluids,the nanomaterials are introduced into the micro-foam drilling fluid to improve the performance of the micro-foam.According to the Box-Behnken Design principle,using the foam comprehensive index as the evaluation standard,the three-factor three-level response surface method is used to optimize the concentration of foaming agent BS-12,hydrophilic nano-Si O₂,and biopolymer XC.The effect of interaction between three treatment agents on the foam comprehensive index was studied.And the mechanism of nanomaterials stabilizing the micro-foam,the factors affecting the particle size distribution of the micro-foam are analyzed.At the same time,a large number of experiments are carried out to optimize filtrate reducer and inhibitor,and to evaluate the performance of drilling fluids.Eventually,a micro-foam drilling fluid suitable for coalbed methane drilling was formed.The drilling fluid composition is0.6%BS-12+4%hydrophilic nano-Si O₂+0.3%XC+3%CMS+0.2%KPAM.The experimental results of drilling fluid performance evaluation show that the micro-foam drilling fluid based on nanomaterials has good rheological property,moderate viscosity and long half-life period.The drilling fluid can effectively inhibit the hydration and dispersion expansion of shale.The linear expansion rate of shale is reduced by 65%compared with that of water,and the rolling recovery rate is increased by 53%.Drilling fluid has good anti-pollution ability,and it can resist 10%salt invasion and 8%coal dust intrusion.The reservoir protection experiments show that after the coal core is contaminated with microfoam drilling fluid,the permeability recovery rate is above 90%.The micro-foam drilling fluid has good carrying cutting capacity.The settling velocity of the coal dust in drilling fluid is 98.3%lower than that of the water,and the rock cuttings settling velocity is 92.8%lower than that of the water.The performance of the micro-foam drilling fluid can meet the requirements of the coalbed methane drilling.