The annular space shall be sealed to protect it against contamination or pollution by entrance of surface and/or shallow subsurface waters. Annular seals shall be installed to provide protection for the casing against corrosion, to ensure structural integrity of the casing, and to stabilize the upper formation.
(a) Minimum depths of seal below ground surface for various uses of wells will be:
| Type Well | Minimum Depth of Seal |
| Commercial, municipal and industrial waste | 30 feet |
| Special process discharge | 30 feet |
| Artificial recharge and miscellaneous discharge | 30 feet |
| Geothermal wells | 30 feet |
| Observation and monitoring | 20 feet |
| Test wells | 30 feet |
(b) Sealing conditions. Following are requirements to be observed in sealing the annular space. - (i) Wells situated in unconsolidated, caving material shall have an oversized hole, at least four inches greater in diameter than the production casing, drilled. A conductor casing shall be installed. The space between the conductor casing and the production casing shall be filled with sealing material. The conductor casing may be withdrawn as the sealing material is placed.
- (ii) Wells situated in unconsolidated material stratified with significant clay layers shall have an oversized hole of at least four inches greater in diameter than the production casing drilled, with the annular space filled with sealing material. If a clay formation is encountered within five (5) feet of the bottom of the seal, the seal should be extended five (5) feet into the clay formation.
- (iii) Wells situated in soft consolidated formations shall have an oversized hole of at least four inches greater in diameter than the production casing. The annular space between the production casing and the drilled hole shall be filled with sealing material.
- (iv) Wells situated in "hard" consolidated formations (crystalline or metamorphic rock) shall have an oversized hole drilled with the annular space filled with sealing material.
(c) Sealing material. The sealing material shall consist of neat cement grout, sand cement grout, bentonite clay or concrete. - (i) Cement used for sealing mixtures shall meet the requirements of ASTM C150 "Standard Specifications for Portland Cement" or API 10B "Recommended Practices for Testing Oil-Well Cements and Cement Additives". Materials used as additives for Portland Cement mixtures in the field shall meet the requirements of ASTM C494 "Standard Specifications for Chemical Admixtures for Concrete" or API RP 10B.
- (ii) Neat cement shall be composed of one sack of Portland Cement (94 pounds) to 4½ to 6½ gallons of clean water.
- (iii) Sand-cement grout shall be composed of not more than two parts by weight of sand and one part of Portland cement to 4½ to 6½ gallons of clean water per sack of cement.
- (iv) Concrete used shall be "Class A" or "Class B". Aggregates shall meet the requirements of ASTM C33 "Standard Specifications for Concrete Aggregates".
- (v) Special quick-setting cement, retardants to setting, and other additives, including hydrated lime to make the mix more fluid or bentonite to make the mix more fluid and reduce shrinkage, may be used.
- (vi) Bentonite clay mixtures shall be composed of bentonite clay and clean water thoroughly mixed before placement so that there are no balls, clods, etc.
- (vii) Used drillers mud or cuttings or chips from drilling the borehole shall not be used as sealing material.
- (viii) The minimum time that must be allowed for materials containing cement to "set" shall be in accordance with ASTM C150 or API RP10B. When necessary these times may be reduced by use of accelerators as determined by the well contractor.
(d) Thickness of seal. The thickness of the seal shall be at least two (2) inches and not less than three (3) times the size of the largest coarse aggregate used in the sealing material
(e) Placement of seal. Before placing the seal, all loose cuttings, chips, or other obstructions shall be removed from the annular space by flushing with water or fluid drilling mud. The sealing material shall be placed when possible, in one continuous operation from the bottom up. The fluid used to force the final sealing material through the casing shall remain under pressure, to prevent back flow, until the sealing material is set.
020-26 Wyo. Code R. § 26-6