Controlling Coal-Fines Production in Massively Cavitated Openhole Coalbed-Methane Wells

Abstract

In the San Juan basin Fairway, cavitated Fruitland coalbed-methane (CBM) wells have been successfully producing for the past 30 years. However, over the years, coal-fines migration into these cavitated wellbores has resulted in pump issues and coal-fines production, leading to a significant decline in production. To clean out the coal fines and replace the pumps on a continuous basis is a costly workover issue. Hence, a foamed remedial treatment was designed to displace the conductivity-plugging coal fines away from the wellbore and immobilize them with the foam also serving as a diverting agent. This has allowed the production and dewatering process to continue without any interruption. The remedial treatment was chosen because the aqueous tackifier in it can control the fines and help prevent them from plugging the flow path. Also, it dissolves any calcium-carbonate scale in the wellbore and near-wellbore region. In this study, 15 cavitated wells with coal-fine issues were selected for the foamed remedial treatment. In all of these 15 wells, the coal-fines issues were resolved. This allowed production to be uninterrupted and reduced the cost of workover rigs and pumps. As a secondary benefit, production stabilized in 10 wells and increased in 5 of these wells. This study shows the production results from these two groups of wells that were treated. It also discusses the design options for the treatments and lessons learned from the process. This technology can be applied to openhole as well as cased multilayered CBM wells.

Experimental investigation on the impact of coal fines generation and migration on coal permeability

“…single-phase flow and two-phase flow) (Bai et al, 2017;Wang et al, 2017), coal fines may plug coal cleats and/or deposit in cleats during the migration process, deteriorating coal permeability. This results in significant drop in the gas productivity (Magill et al, 2010;Palmer et al, 2005). In addition, coal fines can migrate towards a CSG well, burying the downhole pumps, after which workovers will be required to resume the production process (Black, 2011;Okotie and Moore, 2010).…”

Integrated geomechanical, geohydraulic and geological (3G) study of coal fines generation and migration

“…Other coal fines may deposit inside coal cleats during the migration process, narrowing or even totally plugging these natural fractures. This gives rise to significant reduction in permeability ( Figure 1-1(c)) (Harpalani and Schraufnagel, 1990;Magill et al, 2010;Moore, 2012;Palmer et al, 2005). Both phenomena detrimentally affect CSG production efficiency (Black, 2011).…”

“…The common finding is that the birth of coal fines is partially due to the existence of inherent fine coal particles, which are free in flow conduits (Liu et al, 2012;Magill et al, 2010). This kind of coal fines is formed by tectonic deformation, and only takes a small portion of the total fines (Yao et al, 2016;Yao et al, 2015).…”

“…Coal fines are small particles frequently found in coal seams (Magill et al, 2010;Marcinew and Hinkel, 1990), and their sizes are usually between tens of nanometres and tens of microns (Fan et al, 2015;Wei et al, 2015;Zou et al, 2014). With respect to the components of coal fines, Massarotto et al (2013) employed comparative quantitative X-ray diffraction (CQ-XRD) to elucidate that coal material is still the major substance, but with higher fraction of clay minerals than coal seams.…”

“…This may result in a remarkable reduction of coal reservoir permeability, and even blockage in coalbed methane wells or gas drainage boreholes. This can be considered as one of the reasons for significant reduction of coalbed methane production or gas drainage efficiency that in turn causes delays in the subsequent mining operations (Black, 2011;Li et al, 2010;Magill et al, 2010;Narah, 2007;Okotie and Moore, 2010;Palmer et al, 2005;Zhang et al, 2011;Zou et al, 2014).…”