Safety topic: mining development near wells

Across the country, thousands of oil and gas wells are penetrating coal seams that are being actively mined. An inadvertent intersection with one of these pits could pose a hazard to miners through the following types of interactions:

  • If a mine inadvertently crosses an active gas well, methane gas can flood the mining section.
  • Abandoned wells in depleted oil and gas reservoirs can pose similar risks because they can recharge with gas over time.
  • Flooded and abandoned shafts can cause injury by forcing material into the mine or flooding mining sections with water.

Over the past few decades, a lot has changed in the mining and gas industries. Today’s coal mines are deeper, and the proliferation of high-pressure Marcellus and Utica gas wells has increased the potential consequences of an incident. New scientific information is now available, including downhole gas well studies that show that depth has a large effect on the possible discrepancy between a well’s surface location and its downhole location. of coal. Click below to learn more about development mining best practices near gas wells.

Each year, the MSHA and state regulatory agencies evaluate approximately 1,000 extraction applications within 150 feet of oil and gas wells. Historically, the primary technical document addressing the interactions between gas wells and mining in the United States was the “Pennsylvania Joint Oil and Gas Well Gas Well Pillar Study” published in 1957. developed. Today’s coal mines are several hundred meters deeper than they were then, and the proliferation of high-pressure Marcellus and Utica gas wells has increased the potential consequences of a incident. New scientific information is now available, including downhole gas well studies that show that depth has a large effect on the possible discrepancy between a well’s surface location and its downhole location. of coal.

Shaft casing cut by a continuous miner in an active coal mine.

Key Security Practices:

The setback distance from a well must be large enough to mitigate the risks associated with the cumulative impact of the following four factors: 1) Well deviation; 2) survey error; 3) Mining error; and 4) Pillar rib weathering and maximum stress avoidance setback.

The shaft deviation is the horizontal distance between the surface location of the shaft and where it enters the coal seam. Technical support collected data from nearly 250 downhole well deviation readings. The data shows that as wells penetrate deeper, their potential for deviation increases. When the cover (H) is less than 1,000 feet, no well presented deviations greater than H times the tangent of 2°. When H is greater than 1000 feet, the maximum deviation was less than H multiplied by the tangent of 2.5°.

Survey error can be calculated to determine potential location error from the closure rate. Survey error is independent of canopy depth.

Mining error can occur due to out-of-sight mining due to inadequate face survey control, regardless of depth of cover. Frequently establishing aiming points and conducting control surveys mitigates the risks associated with off-site mining sites.

Recoil related to pillar rib alteration and peak stress avoidance addresses the risks associated with penetrating a shaft into the area of ​​the pillar where rib alteration or high deformations of the pillar occur. pillar (yield area). This recoil should also prevent the well from penetrating the pillar in the region where the maximum stress of the pillar occurs, and closer to the lower stress and more stable core.

Resources:

Best Practices – Mining Near Oil and Gas Wells

Overview – Mining near oil and gas wells

White Paper – Mining near oil and gas wells

Jessica C. Bell