The Situation

Bentonite was being used to drill the first injection well on a four-well project. From the point where surface casing was set, hole problems began. The surface casing had to be reset and cemented three times due to drilling fluid migrating up outside of the surface pipe. Following further drilling challenges, logging indicated that the hole had swollen to 24 in. because of highly reactive clays.

The Solution

M-I SWACO engineers were asked to prepare a mud program with additives that would prove effective in inhibiting clay swelling. The following additives were recommended for use on both injection and monitor wells: Max Gel*, Poly Plus*, Platinum Pac UL, Ringfree*, and Poly Plus* LV additives.

The Results

The client realized a $425,000 drilling time savings on injection Well No. 2 as compared to injection Well No. 1 and realized as much as $175,000 in rig time on monitor Well No. 1. The monitor well was drilled using the same mud program as injection Well No. 2 and no hole, fluid or gauge issues were encountered.

When M-I SWACO engineers arrived on the four-well project site, the client was preparing to drill out the cement from the 50-ft (15-m) surface hole on an injection well. The drilling fluid, heavily contaminated with calcium from the cement, was treated with Platinum Pac UL additive and soda ash and the cement was drilled out. The 46-in. hole was drilled to a depth of 500 ft ( 152 m) with no fluid issues, except the need to deviate from the fluid program slightly and increase the yield point to 30 cP and the fluid density to 9.0 lb/gal (4 kg/L) to prevent caving in the sugar sands found to be deeper than expected. The 46-in. hole was then logged and found to be of correct gauge, no swelling; the 34-in. casing was run and cemented with no fluid.

The cement was drilled out of the 34-in. casing and while maintaining a water loss less than 7. At about 950 ft (290 m) Poly Plus LV shale inhibitor/viscosifier was introduced into the fluid system. The well was logged and found to be at gauge, casing was run and cemented with no fluid issues.

The client drilled the final stage to 1,490 ft (454 m) in 32½-in. hole. The well was logged and found to be at gauge and the 24-in. casing was run. Additional drilling was done with reverse air.

The Details

In a comparison between injection Well No. 2 and No. 1 (drilled before M-I SWACO engineers arrived onsite), it was determined that the proposed drilling fluid system used on Well No. 2 saved 17 days, or 60% of time savings ($425,000). This savings less additive cost equals a savings in rig time of $367,000, not taking in consideration lower disposal cost and the cost of additives transferred to the monitor wells. The monitor Well No. 1 was drilled using the same mud program as injection Well No. 2 and had no hole, fluid or gauge issues. Five to seven days rig time was saved on this well. It is anticipated that when the final monitor well is drilled, savings in rig time alone will be in excess of $500.000.

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If you’d like to know more about the HDD Mining & Waterwell products and how they are performing for our other customers, please call the M-I SWACO office nearest you.