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Well Upgrade Technical Report
Section 3 - Field Activities
Field activities were conducted by several subcontractors with oversight from Parsons and CSSA. ECO2 Solutions was subcontracted for water well upgrade work, including carbon dioxide. Well Services of Texas was subcontracted by ECO2 to perform downhole camera surveys of the wells. Venture II, Inc. was subcontracted to remove the pump and piping from Well CS-11. The roof of the prefabricated metal shed was partially removed by Venture II to permit rig access.
3.1 - Carbon Dioxide Treatment Method
ECO2 Solutions, subcontracted to perform the water well upgrade work, uses a unique well treatment which consists of setting a packer (on the end of a schedule 80 steel pipe) at a predetermined depth based on existing well construction and formation information. A flexible hose is used to connect the steel pipe to the carbon dioxide (CO2) control unit and tank. Gaseous CO2 is then injected into the well to depress the water table and force water out of the well. The injection is intended to permit better formation penetration without freezing the water inside the well. When a good flow rate is achieved for gaseous CO2, liquid CO2 is added. A steady pressure increase is maintained. This process can be repeated until a predetermined amount of liquid CO2 product is in the well. The well remains pressurized for at least 8 hours, after which the well may be further pressurized with more CO2 or depressurized to aid formation development. Post-process debris and fines are removed from the formation as the frozen CO2 thaws and formation water re-enters the well. The well may also be further developed with a submersible pump.
Venture II, Inc. was subcontracted under an Armstrong Laboratory/OEB contract with Parsons to remove the pump and piping from Well CS-11 on December 14, 1995. The roof of the prefabricated metal shed was partially removed to permit rig access. The discharge pipe was removed in 21 foot sections. Several pipe sections were extremely pitted and rusted. A crack was noted on the fourth section from the top, running three quarters of the way around the pipe and draining water as the pipe was pulled for disconnection by the rig. The crack occurred at the threaded junction between pipe sections, negating the ability of the drill rig yoke to hold the pipe string in place. Due to the hazard of losing the pipe string, work ceased until CSSA personnel could weld a makeshift collar around the pipe for the drill rig yoke. Removal of the discharge pipe and pump commenced without incident. Removal of the pump and piping revealed the submersible pump was set at 483 feet below top of casing, not 507 feet as previously believed. Pipe sections were placed on wooden timbers and covered with plastic. Due to their poor condition, the pipe sections were scheduled for recycling by CSSA. The submersible pump was wrapped in plastic and placed upright inside the shed. The shed roof was re-attached and the open borehole was closed off temporarily with heavy plastic and duct tape.
The Well CS-11 camera survey performed on May 7, 1997, revealed the following:
| Total depth as measured was 529 feet. | |
| Surface casing was 8-5/8 inch OD and extended to a depth of 213 feet. | |
| All thread and collar casing joints were in sound condition. | |
| Airline pieces were noted from 444 to 513 feet. Discussion with CSSA and ECO2 regarding removal of the airline pieces ended with the conclusion that retrieval was impractical and the debris would not interfere with normal well operation. | |
| The open borehole was moderately tight with only a few small fissures and vugular openings. | |
| A small ledge was observed at 498 feet. |
3.2.3 Carbon Dioxide Treatment
The CO2 treatment was completed for Well CS-11 on May 8, 1997. CSSA purchased a new submersible Jacuzzi pump to replace the existing pump. The old pump was used for development to protect the new pump from debris damage following CO2 treatment. The old pump was then pulled and the new pump put in place. Well CS-11 was developed May 13, 1997 using the old pump and wiring hung from the new column pipe. Total depth was sounded at 535 feet during well development. The discrepancy between the sounding and camera survey total depths (535 feet versus 529 feet) may reflect sediment accumulation at the bottom of the well or the use of differing reference points used for measuring (e.g., ground level versus top of casing). The camera survey depth is considered in this report to be the more accurate measurement of the two. Well CS-11 was developed by pumping overnight. The new submersible pump was set at 510 feet, at the base of 505 feet of column pipe. The e-line access tube for Well CS-11 was set at 120 feet below top of casing.
The camera survey for Well CS-1 was performed on May 7, 1997, and provided the following information:
| The top of the concrete base to which the water supply piping is or was attached was the zero reference mark. | |
| Total depth as measured is 432 feet deep. | |
| The 16-inch surface casing extends for 17 feet. | |
| Static water level was at 96 feet and air bubbles were noted entering the borehole through the formation at 97 feet. | |
| The air bubbles were clearly audible at the surface and noted upon discharge piping and pump removal. | |
| Several zones exhibited good formation development and porosity, alternating with tight formation zones. | |
| Notable porosity was visible at 132, 179, 342, and 365 feet. | |
| Areas containing vugs and small fractures were noted at 211 and 295 feet. | |
| Significant fissures were observed at 331 feet, well developed fractures at 398, 405 and 414 feet, and holes at 427 feet. | |
| Water clarity was good for most of the well with increasing cloudiness at the bottom, suggesting low flow in this region. | |
| Water levels for the wells were higher than typical as central Texas was experiencing a �wet� spring season. |
3.3.2 Carbon Dioxide Treatment
On May 7, 1997 ECO2 subcontractors removed the pump and piping from Well CS-1. The CO2 treatment for Well CS-1 was completed on May 9, 1997. As with Well CS-11, the old pump was used for development of the well after CO2 treatment. The old pump was then replaced with a new submersible Jacuzzi pump.
Based on this observation and recent failures of water quality samples from this well for total coliform, CSSA opted to install new surface casing. On May 14, 1997 the casing upgrade was attempted for Well CS-1. The new casing consisted of 103/4-inch low carbon steel pipe placed as a sleeve within the existing 16-inch (inner diameter) steel casing. The 10�-inch casing was extended to 45 feet where it reached an obstruction, and could not be lowered any farther. Blockages at 35 and 40 feet were also encountered. However, by allowing the casing to free-fall for a short distance, the casing was driven past these initial obstructions. The blockages were determined to be calcium carbonate buildups (similar in genesis to stalactite and stalagmite cave formations) observed during the downhole camera survey. After attempting to drive the casing through the obstruction using a front end loader, it was decided to install smaller, 8-inch OD casing. The smaller casing was placed without complication the following day, on May 15, 1997. The new casing extended to 135 feet. This depth was selected after viewing the downhole camera survey to provide maximum protection from surface and shallow water contamination while preserving as much of the contributing formation as possible. A packer was placed at the end of the surface casing and was composed of several vertical steel bands designed to close the aperture around the pipe during grouting. Clean washed pea-gravel was placed above the basket to ensure its closure. On May 16, 1997, the annulus between the pipe and the borehole (between the old casing and new for the upper 17 feet) was then pressure grouted with a 1:1 mix of clean portland Type II cement.
The discharge pipe was also in poor condition and CSSA chose to replace the existing column pipe. The new pump was placed in Well CS-11 and development of Well CS-1 began and continued overnight on May 17. The well was flushed for 24 hours on May 19. The new pump was placed in Well CS-1 on May 20 followed by a 24-hour run to flush the system. A water level measurement tube consisting of 1-inch schedule 80 PVC pipe was set at a depth of 100 feet.
The Well CS-9 upgrade began November 17, 1997. Pump and piping were removed on the first day. CSSA chose not to replace the existing submersible pump as it had reasonable remaining operational life. The downhole camera survey was run November 18. The Well CS-9 camera survey revealed the following:
| Total depth as measured was 534 feet. | |
| Surface casing was 8-5/8 inch OD and extended to a depth of 23 feet. | |
| All thread and collar casing joints were in sound condition. | |
| Static water level was recorded at 291 feet. | |
| The open borehole was moderately tight above water level with only a few small fissures and vugular openings. | |
| A fracture was noted at 149 feet and a moderate size opening, or hole, at 164 feet. | |
| The formation was fractured with vugs at 350 and 386 feet. | |
| Extensive fracturing and porosity from 390, 444, and 517 feet. | |
| Two large caverns were observed at 490 and 499 feet. | |
| Based on water clarity and porosity, the optimum producing areas of the well appear to be between 390 and 517 feet. |
3.4.1 Carbon Dioxide Treatment
Carbon dioxide treatment of the borehole was performed on November 19. CSSA selected to use new column pipe due to the condition of the old pipe. Based on the camera survey, the pump would be placed at the original depth (532 feet) to accommodate drawdown and low water levels with a PVC shroud above it to channel water flow across the pump body to aid cooling and extend pump life. The open borehole was chlorinated with pool grade chlorine tablets to aid disinfection prior to reinstallation of pump and discharge pipe. Two check valves were placed in the column pipe string, one at 49 feet above the pump intake and the second at 301 feet above the intake. During installation of the column pipe and pump, it was discovered that insufficient wiring remained to set the well at 532 feet. It was concluded by CSSA, Parsons, and ECO2 that the well would not pump dry at this height during extended pumping or drought. Therefore, the pump was set at 504 feet after removing one column pipe segment (21 feet). Well CS-9 was developed and flushed for 24 hours on November 20. The e-line access tube for Well CS-9 was set at 120 feet below top of casing.
Wells CS-1, CS-9, and CS-11 were disinfected in accordance with TNRCC�s guidelines 290.41.3 (f) following well upgrade and development. All standard bacterial testing to meet the state�s safe drinking water requirements was performed by CSSA following well disinfection.