4 Va. Admin. Code § 25-101-200

Current through Register Vol. 41, No. 6, November 4, 2024

Section 4VAC25-101-200 - Plugging of vertical ventilation holes

A. Permit requirements; variances.

1. Plugging operations shall not commence until a detailed plugging plan has been submitted to and approved by the chief. A permit modification is required if the vertical ventilation hole was not previously permitted for plugging.

2. Any person may file an application with the chief to re-plug a previously plugged vertical ventilation hole in any manner permissible under provisions of this section to facilitate the safe mining-through of the vertical ventilation hole at a later date.

3. The chief may, upon application by the permittee, approve a variance to the prescribed plugging methods for the following reasons if it is determined that the alternate plan meets the requirements of §§ 45.2-707 and 45.2-939 of the Coal Mine Safety Act:

a. The coal owner, operator, or lessee of record requests a special plugging program to facilitate mine safety or to obtain approval from another governmental agency for the safe mining-through of a vertical ventilation hole. The application for a variance must include documentation of the request from the coal owner or operator.

b. The permittee has obtained written authorization from the coal owner or operator for alternate plugging of the coal-bearing section. The application for a variance must include documentation of approval by the coal owner or operator.

c. Downhole conditions such as junk in the hole, stuck or collapsed casing, caving or other adverse conditions which would prevent proper execution of the prescribed plugging methods.

d. A permittee presents an alternate plugging plan, which may differ in method from that prescribed herein, but which will achieve the desired result.

B. Plugging in open hole. When a vertical ventilation hole or section of a vertical ventilation hole without casing is to be plugged or plugged back, it shall be sealed and filled as prescribed in this section.

1. At each coal seam, a cement plug shall be placed from not less than 50 feet below the base of the coal to not less than 50 feet above the top of the coal. Whenever two or more coal seams are not widely separated, they may be treated as a single seam and plugged accordingly.

2. If a source of groundwater capable of having a beneficial use is exposed in open hole below surface (water-protection) casing, a cement plug at least 100 feet in length shall be placed below the base of the lowest such groundwater zone.

3. A cement plug of minimum length of 100 feet shall be placed across the bottom of the surface (water-protection) casing. The plug shall be placed so as to have approximately equal lengths in open hole and inside casing. If the vertical ventilation hole is without surface casing, a continuous cement plug shall be placed at least 50 feet below the base of the lowest known aquifer or 300 feet depth, whichever is deeper, to the surface.

4. All intervals below and between plugs shall be filled with drilling mud, bentonite gel, or other appropriately weighted materials approved by the chief.

C. Plugging in cased hole. When a cased hole or section of a cased hole is to be plugged or plugged back, it shall be sealed and filled as prescribed in this section.

1. All perforated intervals shall be either squeeze-cemented or otherwise isolated from the hole by suitable plugs placed across or immediately above the perforated interval. Cement plugs placed across perforations shall extend to at least 50 feet above the top perforations. A cement plug shall be placed to at least 50 feet above squeezed perforations. Cement plugs placed entirely above perforations shall be at least 100 feet in length. At least 20 feet of cement shall be placed on top of bridge plugs, cement retainers, or other tools left in the hole.

2. At each minable coal seam which is behind a properly installed and cemented coal-protection casing, a cement plug shall be placed from not less than 50 feet below the base of the coal to not less than 50 feet above the top of the coal. Whenever two or more coal seams are not widely separated, they may be treated as a single seam and plugged accordingly.

3. If casing is not to be pulled, and there is uncemented annulus behind the pipe, plugging shall be as follows:

a. Each gas or water-bearing stratum present behind the pipe in an uncemented annulus must be isolated by perforating the casing at each zone and squeezing cement up into the zone, or circulating cement up the annulus such that a cement fill up of not less than 100 feet is achieved. When squeezing or circulating the annulus, a cement plug of at least 50 feet shall be placed inside the casing above the perforations.

b. If there is uncemented annulus between an inner casing and the coal-protection string, the casing shall be perforated to allow cement to be circulated over the prescribed interval, and a plug of equal length shall be placed inside the inner casing.

c. If a fresh water aquifer is exposed to the hole in an uncemented annulus, it shall be isolated by perforating the casing at least 100 feet below the aquifer and squeezing cement into the annulus or circulating it up the annulus so that a fill-up of not less than 100 feet is achieved. When squeezing or circulating cement, a cement plug of at least 100 feet shall be placed inside the casing above the perforation.

d. At a point no less than 50 feet below the bottom of the surface (water-protection) string, the casing shall be perforated and cement circulated up the annulus to a minimum fill-up of 100 feet. A plug of equal length shall be placed inside the casing.

e. From a point not less than 50 feet below the surface, a cement plug shall be installed which reaches the surface. If any uncemented annuli are present at the surface, the voids should be filled and sealed to the greatest extent possible by introducing cement from the surface.

f. All intervals below and between plugs shall be filled with drilling mud, bentonite gel, or other appropriately weighted materials approved by the chief.

4. If casing is to be pulled, plugging shall be as follows:

a. All perforated intervals shall be isolated as described in subdivision 1 of this subsection.

b. Casing stubs shall be isolated by placing a plug across or above the cut-off point. Cement plugs shall be at least 100 feet in length and shall be placed so as to have approximately equal length inside and above the remnant casing. Permanent bridge plugs may be placed above the stub and shall be capped by at least 20 feet of cement.

D. Plugging operations involving uncemented water-protection casing or coal-protection casing.

1. If the annulus of the largest casing present across a minable coal-bearing section is not cemented across that section, then one of the two procedures listed below must be followed:

a. The casing must be perforated at least 50 feet below the lowest coal seam, and cement circulated in the annulus to the surface (if water-protection casing is absent or not properly placed and cemented to surface), or to at least 100 feet above the highest coal (if the casing is to be partially pulled to facilitate plugging operations in the fresh water zone). Plugging shall proceed according to cased hole requirements; or

b. The casing shall be pulled from the hole, and plugging shall proceed according to open hole requirements.

2. If the annulus of the largest casing present across the fresh-water-bearing section is not cemented across that section, then one of two procedures listed below must be followed:

a. The casing shall be perforated below the lowest known fresh-water zone or at a minimum depth of 300 feet. Cement shall be circulated in the annulus to the surface. Plugging shall proceed according to cased hole requirements; or

b. The casing shall be pulled from the hole, and a continuous cement plug shall be placed from below the base of the lowest known fresh-water aquifer exposed to the hole or 300-foot depth, whichever is deeper, to the surface.

E. Unfillable cavities. When an unfillable cavity, such as a cavern, mine void, blast stimulation zone, or gob completion is encountered, the section shall be plugged as follows:

1. If the stratum with the unfillable cavities is the lowest stratum in the hole, a plug shall be placed at the nearest suitable point not less than 20 feet above the stratum. Cement plugs shall be at least 100 feet long, and at least 20 feet of cement shall be placed on top of bridge plugs.

2. If the stratum with unfillable cavities is above the lowest stratum, a plug shall be placed below the stratum and shall extend to within 20 feet of its base. A plug shall also be placed above the stratum as described in subdivision 1 of this subsection.

4 Va. Admin. Code § 25-101-200

Derived from Virginia Register Volume 17, Issue 20, eff. July 18, 2001; Amended, Virginia Register Volume 38, Issue 13, eff. 3/31/2022.

Statutory Authority: § 45.2-103 of the Code of Virginia.