Study of borehole stability of Marcellus shale wells in longwall mining areas

Abstract

With the widespread drilling of gas wells in Marcellus shale, there are high potentials for wellbore instability problems when wells are located in longwall mining areas, which in many areas such as southwest Pennsylvania, West Virginia, and eastern Ohio are being used for extraction of the coal seam overlaying the gas reserves. The ground deformation, caused by coal mining, could generate large horizontal displacement and complex stress change in subsurface rock. This in turn triggers ground movement which can cause casing failure, and thus interruption in the operation of the well that raises safety and environmental concerns. This could result in shutting down the well for repair, or permanent abandonment. Thus, it is critical to characterize the parameters related to the longwall mining process and to propose a general casing design guideline in such areas. In this paper, numerical modeling was utilized to simulate the complex ground conditions and resulting stresses and strains in longwall mining areas. A casing design spreadsheet was then constructed for design of appropriate selection of casings, based on the results of the numerical modeling. Our results were validated with field practices of wellbore design in southwest Pennsylvania. This paper also provides a methodology for investigating potential ground deformations, resulting stress/strain changes, and wellbore stability issues for oil and gas wells drilled in longwall mining areas in Marcellus shale or similar formations worldwide with active coal mining activities.

Severe wellbore instability in a complex lithology formation necessitating casing while drilling and continuous circulation system

“…Other wellbore stability works focused on sandstones such as Kolawole et al (2018). There are several wellbore stability works on shales in recent years (Wang et al 2014).…”

Influence of Stratigraphic Conditions on the Deformation Characteristics of Oil/Gas Wells Piercing Longwall Pillars and Mining Optimization

“…To successfully maintain the yield of the wells that act as the conduits for the transmission of hydrocarbon resources from the underground reservoir to the surface, it is critical to ensuring the stability and security of these hydrocarbon wells during their service life. However, in some sedimentary basins where coal, gas and oil coexist, such as the Ordos basin, China, and the Appalachian Basin, in the United States, ensuring the stability of wells traversing coal seams is becoming a daunting challenge, adversely impeding the simultaneous recovery of coal and hydrocarbon resources [1][2][3][4][5][6][7][8]. The extensive and intense strata movement and deformation induced by longwall coal mining may result in large deformations and potential failure of the hydrocarbon wells.…”

Topographic influence on stability for gas wells penetrating longwall mining areas

“…Borehole failure mechanisms are also important in determining the integrity of the well (Aadnoy and Chenevert, 1987;Gough and Bell, 1981;Haimson and Song, 1993;Tan and Willoughby, 1993;Tan et al, 1998;Zheng et al, 1989;Zoback et al, 1985) and may also be used to determine the orientation of in situ stresses. One reason is that the importance of unconventional natural gas reservoirs underlying mineable coal seams has only become an important issue relatively recently (Wang et al, 2013). Despite a significant number of studies relating to well stability for hydrocarbon wells, relatively fewer results are available to define stability under the influence of strata movement and control, or of the effects of pillar crushing.…”