SDBS-Induced Dispersion Effect of High-Rank Coal Fines to Inhibit the Conductivity of Propping Fractures

Coal fines are commonly produced in the form of aggregatesduringthe development of coalbed methane (CBM), which significantly restrictsthe well productivity. Specifically, the reunion state of coal finesplays a key role in impacting the conductivity of propping fracturesafter fracturing. In this work, the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) was selected to control the reunion stateof coal fines. Visualized simulations of coal fines' transportbehavior in proppants with different particle sizes were carried outunder low constant pressure based on sand pack experiments. Moreover,the characteristics of coal fine filling and production in proppingfractures were obtained. The results indicate that SDBS has a dispersioneffect on coal fine aggregates in the KCl fracturing fluid, with anaverage reduction of 36% in particle size. There is a positive correlationbetween the proppant size and the permeability coefficient of proppingfractures. Coal fines reduce the permeability coefficients obviously,which first rapidly decrease and then slowly reach a stable stage.In the first stage, the changes of permeability coefficients are affectedby the relative particle sizes of the proppant and the coal fine,which is consistent with the classic 1/3 sealing mechanism. In thesecond stage, SDBS increases the amount of coal fines between theproppant pore throats, and the thickness of the filter cake formedfrom coal fines at the entrance of the propping fracture increases,resulting in the inhibition of fracture conductivity. Additionally,the output of coal fines is increased dramatically induced by SDBS.Finally, the inhibitory effect of SDBS on fluid production was verifiedby comparing the water production and coal fine content of two fieldwells CW # 1 and CW # 2. This study has guiding significance for theoutput and control of coal fines in low-pressure production of CBMwells.