Kaolinite flakes and coal fines production in lignite core under ambient conditions: A case study of Neyveli Lignite Field at Cauvery Basin, Southern India

Coal fines production and structural collapse during waterflooding process was widely observed and reported in several coalbed methane (CBM) fields. Besides, fines migration also plays a major role in the destruction of coal cleats and consequently, declining the gas recovery. This paper presents the coal fines production in lignite core as a function of kaolinite. Actually, it is a clay fine particle that rests on coal surface under the dominances of the four forces, namely, lift, drag, gravity, and electrostatics. Under hydrodynamic and thermodynamic forces these fines detach from the rock surface and migrate in the porous interspace, and at a certain point it is captured, and thereby deteriorating the well productivity and structural collapse as well. Many researchers have investigated these fines migration mechanisms in anthracite and bituminous coals, but to best of our knowledge fill date this research was not carried out in lignite coals. In order to successfully demonstrate this mechanism in lignite, three sets of coreflood experiments have been conducted under ambient conditions for analyzing the coal and kaolinite fines transport and their impact on gas recovery. Lignite samples are procured from Neyveli Mines at Cauvery Basin in Southern India and then the simulated version is used for the analysis. The coreflood results revealed that the gas recovery increases for increasing PVI and that there is an observation of pressure drop across the core for increasing PVI and this phenomenon is attributed to enhancing concentration of fines. Additionally, the water flow velocity elevates the velocity of coal fines and the microstructural analysis indicated the presence of kaolinite flakes among coal fines. The entire experimental model was tested against the statistical model in SPSS and showed good agreement. Overall, it is understood that even lignite reservoirs are prone to fines migration and permeability decline.