Table of Contents

Vol. 8, No.3
3rd Quarter 2002

Coiled Tubing Inflatable Straddle Acidizing Packer (ISAP)

Chemical placement techniques for live well interventions have evolved from basic through-tubing methods such as bullheading to through-tubing inflatable packers on coiled tubing. This enables precise placement of chemicals without having to pull the completion. Baker Oil Tools' ISAP Inflatable Straddle Acidizing Packer System (ISAP) consists of three major sub-assemblies: an injection control valve, a mechanical control or spotting valve, and a packer section. The system is controlled downhole by manipulating the injection and mechanical control valves. Inflation and deflation are controlled through hydraulic manipulation of the injection valve. The tension-operated mechanical control valve opens or closes an unloading flow path between the treatment interval and the annulus, above the packer section.

Several features make ISAP technology more positive and precise than previous methods of selective placement: (1) only a slight amount of tension and no required set-down weight helps in horizontal and highly deviated wellbore applications, (2) activation with only up-and-down movement and pressure is well suited for coiled tubing operations, and (3) re-settability allows it to be used to wash perfs, test tubing, and perform other jobs on coiled tubing. Although the tool has been used for as many as 22 settings in one run, 4-16 settings per run are most common.

For ISAP product information, visit Baker Hughes website (www.bakerhughes.com/bot/inflatable_packers/pdf/ISAP_brochure.pdf)

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Progress in Commercializing Compressed Sodium Bentonite P&A Process

Beginning in late 1999, Chevron Environmental Management Company initiated a program of using highly compressed sodium bentonite for plugging wells. Compressed sodium bentonite is self-healing, retaining latent swelling ability that allows it to maintain a seal over extremely long timeframes. The patented procedure relies on the bentonite, once placed and exposed to fresh (low chloride) water, hydrating and expanding to form a sealing plug. Unlike conventional cements, the bentonite can continue to hydrate, forming a "living plug" which adapts to its environment (i.e., if something shifts or moves, the plug adapts and retains the seal). Process simplicity provides a favorable economic and safety benefit. Methodology contemplates a surface pour operation, thus eliminating certain equipment requirements.

As earlier reported in Network News (March 2001), a pilot program was initiated, working with the California Division of Oil, Gas and Geothermal Resources, and the California regional BLM office. The pilot included approximately 110 wells. The pilot was an operational success and significant cost savings were realized, so Chevron decided to commercialize the technology forming a wholly-owned subsidiary, Benterra Corporation, in October 2000. Benterra implemented a multi-phase commercialization plan.

Phase 1 was the evaluation of the technology, Phase 2 was the introduction to industry and regulatory agencies, and Phase 3 is the transfer of the technology to other industry partners. In April, 2001, a Field Guidance Document for California was approved. Key regulatory criteria included the specific gravity of both raw material and the hydrated plug, volumetric calculation methods for determination of placed material, witnessing of tags, and well deviation and depth limitations. Since regulatory approval, over 600 wells have been abandoned using this methodology in California.

Pilot programs have now been successfully completed in 2001 and 2002 in the states of Oklahoma, New Mexico and Pennsylvania. A pilot program is currently in progress in Texas, with an expected completion by year end. At this time, the new process has regulatory approval, with some local restrictions, in California, Kentucky, New Mexico, Oklahoma, Pennsylvania and Utah. This has led to an IOGCC Environmental & Safety Subcommittee issuing a Bentonite Plugging Report, due by the end of the year.

To date, Benterra has plugged more than 1200 wells utilizing the compressed sodium bentonite technology. The deepest well where the procedure has been applied is 7,500 ft. Procedures are rapidly evolving, and the field database is expanding. Benterra is currently transitioning from Phase 2 to Phase 3 and expects to solicit industry interest in 2003.

Article courtesy of Barry Salsbury, Benterra Corporation, email BarrySalsbury@ChevronTexaco.com

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Through Casing Sampling with CHDT Tool

Conventional alternatives for testing and sampling through casing require perforating the casing, performing a test between packing elements, and then squeezing off the perforations. Although Schlumberger's modified Repeat Formation Tester made some progress, there were still serious limitations. A new Cased Hole Dynamics Tester (CHDT) tool developed by Schlumberger and the Gas Technology Institute is a definite step forward. 

The tool can drill up to six precise sampling tunnels per trip, acquire multiple formation pressures, retrieve formation-fluid samples and restore pressure integrity by plugging the holes it drills. The tool can be conveyed on wireline, on drillpipe or with a tractor. The tool first is run to the target depth, then anchor shoes push the tool packer against the casing to provide a seal. After the seal is verified, a hybrid bit on a flexible drill shaft starts to drill. The tool can drill up to 6 in from the internal surface of the casing. Reducing the pressure of the fluid surrounding the bit prior to drilling enhances the pressure response when communication is established with the formation. 

Once the bit encounters the formation, measured pressure stabilizes at reservoir conditions and drilling stops. For drawdown analysis, the tool can perform multiple pretests at various rates with volume up to 100 cm3. Samples can be collected once communication is established between the tool and the formation. After pressure testing and sampling, the tool inserts a Monel plug, rated to a differential pressure of 10,000 psi, to seal the casing. 

Devon Canada Corporation applied the CHDT tool in the Dunvegan Debolt reservoir, an 800 ft reservoir with up to 15 productive intervals. Developed in the 1970s, the field is about 50% depleted. In selecting infill drilling locations, knowing the pressure of different zones was critical. Devon measured pressure in eight zones in a well using the CHDT tool. All holes were successfully plugged. Pressure data indicated that six of eight zones in the infill well were of reservoir quality. Of these, drainage was detected in one with lower than expected pressure, while higher than expected pressure in another zone pointed towards undrained reserves. Results have been helpful in optimizing well placement as infill drilling proceeds. 

Summarized from "Formation Testing and Sampling Through Casing," GasTIPS, Summer 2002, p. 32-36. Visit SCNG's website (www.netl.doe.gov/scng/index.html) to see when Summer 2002 article of GasTIPS placed online.

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