An advanced system of drill stem testing equipment makes testing from floating vessels a more efficient operation. Introduction of a pressure responsive circulation valve completes the system where all normal testing functions can be completed by controlling annulus pump pressure and without pipe manipulation. This includes repeated operation of the testing valve, isolating a sample, and reverse circulation. Depth range of equipment has been extended and high flow-rate provisions included. All of this has been done without sacrificing fail-safe features or basic principles which characterize original pressure-operated equipment.
Tools and techniques used on land have been replaced by new concepts and equipment fortesting wells from floating vessels. Realization that this service often evaluates the need for a $5- to $25-million development-well platform1 is adequate incentive for use of the very best testing equipment and procedures. Simplifying operations and at the same time providing maximum safety have always been primary considerations. Vessel movement during necessary operation of tools before, during, and after a test has been a source of difficulty.
Some of these problems were dealt with satisfactorily with the addition of the volume balanced slip joint, slip joint safety valve, subsea test tree, and the annulus pressure operated safety sampler.2.
Although these tools represented significant progress in making drillstem testing from floating vessels a safer operation, some had limitations inherent in their use. The limitations of these tools prevented their operation from being completely practical for all well conditions.
For example, continued reliance on rotating the drill pipe, dropping a bar, or using a pump out device to initiate reverse circulation, retained problems that had not been satisfactorily solved. Field experience with these original tools and recognition of such problems resulted in new designs and techniques that promise more complete and practical solutions. The result is a new generation of drill stem test assemblies that will be discussed in this paper.
In 1964, the volume-balanced slip joint became the first tool introduced specifically to aid in formation testing from floating vessels. It provided a way to maintain constant weight on the packer and hydraulic tester while the vessel and suspended drill pipe moved. The slip joint is placed a specified distance above the — testing tools to insure sufficient weight below it to seat the packer and open the tester. Pipe or drill collars below this telescoping joint remain stationary (except during necessary tester positioning) despite vessel movement caused by waves, swells, etc.
Introduction of the slip joint safety valve, which was attached to the bottom of the slip joint, provided the first down-hole device intended to automatically keep a well under control when unexpected or disastrous events occurred. Characteristically, the oil industry has always tried to foresee the worst thing that could happen and be prepared for it.