Key strata characteristics controlling the integrity of deep wells in longwall mining areas

Shun Liang, Derek Elsworth, Xuehua Li, Xuehai Fu, Boyang Sun, Qiangling Yao

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The damage of vertical oil/gas wells in longwall mining areas is mainly a result of strata movement induced by coal extraction. Strata with contrasting lithology vary dramatically in their movement and potential for well damage, with some special combinations of strata in particular having the greatest potential for damage. This study investigates the effects of specific combinations of strata transition structures ((i) topsoil-bedrock, (ii) a thin weak interlayer sandwiched above and below by two stiff beds, and (iii) the key-stratum sandwiched above and below by two soft beds) on the magnitude, severity and distribution of various anticipated well deformations, and explores the optimal drilling path for wells to maximize well integrity. Results indicate that: (1) Effects of various combinations of strata on well deformation lie essentially in the mismatch in the mechanical properties of the strata and weak interfaces, with the stratum thickness and vertical distance from the coal seam to the stratum/interface also exerting a significant influence. (2) Wells in the upper part of the topsoil are subject to horizontal tension, while the lower part is laterally compressed following the extraction of either one panel or both panels. Large lateral tensile strains normally arise at the upper part of the hard strata which directly underlie the soft strata. Large lateral compressive strains are concentrated in the strata within ~ 5 m above and below the coal seam and peak in the seam. Longitudinal well deformation is dominated by compression in soft strata, especially in the upper part of the layer, and is dominated by tension in stiff strata, within the lower portion in particular. Vertical compression at the interface is larger below the key-stratum, and peaks at the interface between the coal seam and its immediate roof. Well distortions in soft strata are 3 to 5 times those of ones in stiff strata. (3) Well deformations developing both at interfaces and within layers significantly intensify in the vicinity of the seam. An integrated consideration of various deformations of five candidate well paths indicates that the optimal position for well stability is the one that deviates from the pillar centerline and is close to the second mined panel.

Original languageEnglish (US)
Pages (from-to)31-42
Number of pages12
JournalInternational Journal of Coal Geology
Volume172
DOIs
StatePublished - Mar 1 2017

Fingerprint

Longwall mining
longwall mining
well
Coal
coal seam
damage
topsoil
compression
Lithology
Tensile strain
oil well
gas well
Gas oils
pillar
Roofs
roof
mechanical property
Drilling
bedrock
lithology

All Science Journal Classification (ASJC) codes

  • Fuel Technology
  • Geology
  • Economic Geology
  • Stratigraphy

Cite this

Liang, Shun ; Elsworth, Derek ; Li, Xuehua ; Fu, Xuehai ; Sun, Boyang ; Yao, Qiangling. / Key strata characteristics controlling the integrity of deep wells in longwall mining areas. In: International Journal of Coal Geology. 2017 ; Vol. 172. pp. 31-42.
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Key strata characteristics controlling the integrity of deep wells in longwall mining areas. / Liang, Shun; Elsworth, Derek; Li, Xuehua; Fu, Xuehai; Sun, Boyang; Yao, Qiangling.

In: International Journal of Coal Geology, Vol. 172, 01.03.2017, p. 31-42.

Research output: Contribution to journalArticle

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