Critical Conditions for Massive Fines Detachment Induced by Single-Phase Flow in Coalbed Methane Reservoirs: Modeling and Experiments

Abstract

Fines migration has posed a great challenge to gas and water production in CBM reservoirs, resulting not only in dramatic permeability reduction but also in excessive wear on equipment. The objective of this study was to investigate critical flow conditions for massive fines detachment in the dewatering phase, for the purpose of yielding an improved understanding of fines detachment mechanisms and their effective control in the field. First, fines migration experiments under saturated conditions, including effluent concentration and permeability measurements, were conducted at elevated pressure gradients on fractured coal samples with various apertures. Experimental results indicate the existence of a critical pressure gradient (CPG) for massive fines detachment. Second, a mathematical model was developed to describe single particle detachment in the fracture, accounting for the coupling effects of hydrodynamic and extended-DLVO forces. Effects of fines size and fracture aperture on fines detachment were analyzed, and CPGs were determined from the proposed model. Modeling results revealed that the pressure gradient required for fines detachment first decreased with increasing fines size, reached a minimum value, and then increased; these minimum values are defined as CPGs, which exhibit a strong negative correlation with fracture aperture. CPGs obtained from modeling were slightly smaller than those determined from experiments, due to the assumptions of homogeneous surfaces and spherical particles in the model. Finally, the implications of this research on field-scale fines control in coal were thoroughly discussed.

Effects of Proppant Wettability and Size on Transport and Retention of Coal Fines in Saturated Proppant Packs: Experimental and Theoretical Studies

“…3−8 During the process of CBM recovery, hydrodynamic and/or capillary forces are exerted on in situ coal fines. 9,10 When the incipient motion condition of coal fines is satisfied, coal fines get detached from the channel surface and are entrained by the fluid. 10−13 The transport channels in CBM reservoirs can be divided into the following three types: natural cleats/fractures, propped fractures, and boreholes.…”

“…However, in the natural environments, coal fines and proppants are highly irregular and exhibit various shapes. 9,84 Moreover, the surfaces of coal fines and proppants are physically (roughness) and chemically (wettability and zeta potential) heterogeneous. 85 The irregular shape and surface heterogeneity affect not only the fines− proppant interaction energy (adhesive fore), but also the flow field (hydrodynamic forces) in the vicinity of the proppant, consequently influencing the retention of coal fines.…”

“…Theoretically, Mitchell and Leonardi 30 carried out a numerical simulation of detachment and mobilization of coal fines in cleats/fractures during single-phase water flow by using the combination of the lattice Boltzmann method (LBM) and the discrete element method (DEM). Huang et al 9 also proposed an analytical model for fines detachment based on the analysis of hydrodynamic and adhesive forces/torques acting on fines, to elucidate the mechanisms for fines release induced by single-phase water flow in fractures. Furthermore, the transport and retention behaviors of suspended coal fines in fractures were also investigated by Han et al 15 They found that the deposited amount of coal fines decreased with the increase in the fracture width, while increased first and then decreased with the increasing flow rate and fines concentration.…”

Permeability Damage and Supercritical Fluid Storage in the Cauvery Basin Neyveli Lignite Bed Containing Kaolinite Deposits during Alternative Injection of Brine and CO2

“…This section presents the variation of coal nes velocity and kaolinite nes concentration with respect to increasing pore volume injection (PVI). Massive coal nes are produced due to external uid invasion, usually, water through the coal formation excessive wear under critical ow conditions (Huang et al 2017). It can be seen from the Fig.…”

Numerical Simulation Study of Fines Migration Impacts on an Early Water Drainage Period in Undersaturated Coal Seam Gas Reservoirs

“…In the undersat-urated CSG reservoirs, not only the fluids but also the transport of solid particles occurs in the coal cleats during the early water drainage period. Because of the high fragility, coal rock often generates large numbers of fines in drilling, stimulation, and water drainage processes [7][8][9].…”