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Geothermal Zonal Isolation

 

Gels for Zonal Isolation While Drilling

DOE’s Energy Efficiency and Renewable Energy (EERE) objectives are to advance technologies to make it more cost effective to develop, produce, and monitor geothermal reservoirs and produce geothermal energy. More specifically this includes the Geothermal Technologies Program (GTP) goals for geothermal zonal isolation which include: 

    • Operating with differential pressures of up to 6000 psi in wellbore diameters of 6 5/8” to 10 5/8”, retrievable hardware operation period of greater than 14 days, and
    • Temporary sealing fracture openings from 2” to less than 1/16” wide, under up to 500 psi Δ P and up to 300C, for an operation period of up to 60 days.

This translates into this project’s goal to determine if SPI gel products can be generated for High Temperature High Pressure (HTHP) operations that form hard, solid gels with some level of elasticity, as in other applications. Such strong gels that are tolerant of high temperatures were demonstrated in this project to date.

High temperature oven.

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High pressure testing device.

 

Zonal isolation is critical to well drilling success and cost, as well as ensuring long term optimal reservoir performance.  Traditional cementing of lost circulation or thief zones during drilling is often done to stem the drilling mud losses and allow drilling to progress.  This is an expensive and generally unsuccessful technique losing the potential of the remaining fracture system. Alternative mechanical methods are very expensive and the HTHP elastic seals used often fail at these EGS conditions. Selective placement of strong SPI gels into only the offending fractures can allow continued drilling to the total depth desired as well as maintain and even improve operational efficiency of the resource and extend its economic life.  Also realize that this technology could solve lost circulation (zonal isolation) drilling problems in oil and gas wells at lower temperatures using hard gels similar to what one would use for casing leak applications.

Fortunately, the formulations used for CO2 flooding were tested to 180 oF and found to be tolerant for that application.  When these same formulations were modified, they were found to be extremely tolerant to the 350F temperatures encountered in the initial oven testing.  These results were reproduced at 450F and again at 600F.  Dynamic testing resisted a Δ P over 1,000 psi with the top of the sand pack open at a temperature of 200F. This Δ P phenomena was verified at 300F space velocities. These are the type of results we hope to build upon in Phase II effort.  This system will primarily become an inorganic system that can tolerate the 600F temperatures. This is “Proof of Concept” successes necessary to justify a DOE Go Decision to progress into Phase II.