Method and apparatus for testing wells using dual coiled tubing

Abstract

A new drill stem test apparatus and corresponding method includes a dual coaxial coiled tubing adapted to be disposed in the wellbore. The dual coaxial coiled tubing includes an inner coiled tubing, and an outer coiled tubing surrounding and enclosing the inner coiled tubing and forming an annular space which is located between the inner coiled tubing and the outer coiled tubing. The annular space is adapted to contain a pressurized kill fluid. A first end of the outer coiled tubing is sealed by a sealing element to a first end of the inner coiled tubing, the end of the inner coiled tubing extending beyond the sealing element and adapted to receive a formation fluid. The first ends of the inner and outer coiled tubing are disposed in a wellbore. A second end of the inner and outer coiled tubing is wound onto a coiled tubing reel and is connected to a kill fluid valve and a formation fluid valve. When the kill fluid valve opens while the formation fluid valve is closed, a pressurized kill fluid fills and pressurizes the annular space between the inner and outer coiled tubing. While the kill fluid valve is still open, the formation fluid valve is opened. A formation fluid begins to flow from the formation through the inner coiled tubing and through the formation fluid valve. If the inner coiled tubing forms a hole and begins to leak formation fluid, the pressurized kill fluid in the annular space will prevent the formation fluid in the inner coiled tubing from leaking out of the interior of the inner coiled tubing and into the annular space.