Experimental research on the generation of solid fines from muddy intercalation in water-rock reaction

Under the dual control of coal reservoir geological conditions and CBM development engineering,the genera- tion and migration of solid fines,which mainly are coal fines,has a particularly severe restriction on the continuous and stable production of CBM wells. To identify the impact of complex coal bed texture on the gener-ative rule of solid fines in CBM development,taking the core sample with superimposed coal seam and muddy intercalation as a research ob- ject,the physical simulation experiment of water-rock reaction (WRR) was carried out by using single-phase water flow core flooding rig. The amount,types and migration features of solid fines and their damage on glass beads layer (GBL) conductive ability were contrastively analyzed,which were generated separately from muddy intercalation and coal seam with KCl solution of different concentrations. The results show that under the same conditions of physical simulation experiment,muddy intercalation can easily generate more clay mineral solid fines with smaller particle size in WRR compared to coal seam. The concentration of KCl solution affects the rule of solid fines generation from muddy intercalation,high intensity WRR between the KCl solution of low concentration and muddy intercalation can be pro- duced,which causes the increase in the generative amount and migration rate of solid fines. The damage on the con- ductive ability of GBL can be caused by the cementation and retention of solid fines,with the increase of solution con- centration,the generative amount and migration distance of solid fines declines,which reduces the duration of the de- crease extent of permeabil-ity fluctuation accordingly. Combined with the research on CBM development practice at Hancheng mining area in Weibei Carboniferous-Permian coal-field,it is concluded that the CBM production in coal seam with complex texture can increase the layers and thickness of parting,diversify its lithology and complicate its mineral compo-nents,which will weaken the stability of mineral composition and rock structure of muddy intercalation and other sensitive rock formations in the combined influence of stress rupture and WRR,lead to the generative types of solid fines in coal reservoir becoming complex and diverse,increase the generative intensity and migration distance of solid fines,and then result in more serious reservoir damage and frequent equipment failures,which directly affects the production of CBM wells. By ascertaining the spatial development characteristics,types and contents of sensitive minerals of parting in CBM development layers,anti-swelling agent and stabilizer can be used properly in drilling,frac- turing and workover to reduce the degree of clay mineral expansion and dispersion,increase the surface hydrophobicity of coal and improve the adhesion force of coal fines in the fracture surface,which could reduce the generative amount and migration rate of solid fines and then the issue of solid fines production in coal reservoir can be effectively con- trolled.