Migration And Control Of Pulverized Coal In Gas Production Channel For CBM Well

In the process of CBM development,the output of pulverized coal is one of the key factors affecting the continuous and stable drainage of CBM wells.Therefore,formulating reasonable pulverized coal prevention and control measures plays an important role in the high and stable production of CBM wells.This paper takes a mining area in the south of the Junggar Basin as the research object,and takes the 42-43 and 45 coal seams of the Middle Jurassic Xishanyao Formation as the target coal seams.Using a combination of laboratory experiments and theoretical analysis,a systematic study was carried out on three aspects of the CBM wells in the study area,the characteristics of pulverized coal production,the migration law of pulverized coal in the gas production channel,and the prevention and control mechanism and measures of pulverized coal.,Concluded as follow:(1)The target coal seam contains a large amount of clay minerals,which increases the potential of the target coal seam to generate pulverized coal;the pore and fracture system of the target coal seam is well connected,creating favorable conditions for the migration of pulverized coal.(2)The pulverized coal particle size range of CBM wells in the study area is large,and the Zeta potential of pulverized coal particles in different fracturing fluids is different.(3)Agglomerated fracturing fluids(1.5% KCl + 0.05% KO)and dispersive fracturing fluids(1.5% KCl + 0.06% SA)were selected to realize the free control of pulverized coal agglomeration and dispersion behavior.(4)The accumulation form of pulverized coal in distilled water,active water fracturing fluid,agglomerated fracturing fluid and dispersed fracturing fluid is roughly the same,that is,in the fracture channel,pulverized coal gradually accumulates,forming point-like accumulation,Linear accumulation,block accumulation and blockage;In the natural fracture channel,the migration modes of pulverized coal mainly include horizontal migration,slow rise,slow fall,rolling,etc.;In the fracture channel supported by fracturing,when the pulverized coal is deposited along the streamline without causing blockage,the front-end sedimentary shape presents strip-like divergence,and then evolves into "massive deposition","flame-like accumulation","linear accumulation" and "scattered point accumulation";However,under the same conditions,there is a big difference in the amount of pulverized coal accumulated in the observation unit,showing a trend of dispersed fracturing fluid>distilled water>active water fracturing fluid>agglomerated fracturing fluid.(5)Compared with distilled water,active water fracturing fluid and dispersed fracturing fluid,agglomerated fracturing fluid can effectively alleviate the permeability damage caused by pulverized coal to fracturing propped fractures,and achieve effective prevention and control of pulverized coal.The mechanism of prevention and control is:the agglomeration fracturing fluid can change the wettability of the pulverized coal and increase its cohesion,so that the pulverized coal particles can aggregate and settle during the migration process.Thereby reducing the number of suspended pulverized coal particles,effectively reducing the output of pulverized coal and the damage rate of fracturing support fracture conductivity.(6)It is recommended to use low-damage agglomerated fracturing fluid for reservoir strengthening,which can prevent coal dust and prevent water sensitivity,water lock and speed sensitivity;It is suggested that a "continuous,slow and stable" drainage system should be formulated for CBM wells.Only under this premise can agglomer-ated fracturing fluids be able to effectively prevent and control pulverized coal.