Developments in Testing from Floating Vessels
Authors: Wray G.Q. , Petty G.E. , Jeffords C.M. 
Published: December 2007

New developments in formation testing equipment provide more safety and better performance in offshore floating vessel operations. A slip-joint safety valve, for example, will help close in a well in certain emergencies. Field tests on another device-the annulus pressure responsive safety valve-have shown that it, too, satisfies pressure responsive safety valve-have shown that it, too, satisfies the unique requirements of such testing operations.

Introduction

Benefits of formation testing were proved long before off-shore drilling operations were commonplace. This temporary completion service gives the owner valuable information for evaluating well potential. Years of research have been spent in developing tools for obtaining this information efficiently and safely. Stationary offshore rig operations utilized standard land testing procedures; however, this technology had to be expanded for testing from floating vessels under various sea conditions. The unique needs of testing from floating vessels have led to such developments as the balanced slip joint, the slip-joint safety valve, the subsea test tree and the annulus pressure responsive safety valve (APR safety valve).

Conventional land testing assemblies were used on the first tests from floating vessels. Since the vessel moved up and down at the will of tides and waves, it was difficult to maintain the drillpipe stationary to keep recommended weight on a packer. Little, if any, specialized safety equipment was available.

Introduction of volume-pressure balanced slip joints was a great improvement in the offshore testing string. It allowed testers to set and hold a desired amount of weight on the packer and yet safely manipuulate drillpipe to operate testing tools above the packer. Such slip joints help compensate for wave and tide actions, making safer the task of testing from floaters.

Normally, testing tools are opened by applying pipe weight. However, pipe can part up-hole when floating vessels break anchor and drift off location or when unusual wave action is encountered, and this leaves tools in an open position with no down-hole means for closing the well. Development of a slip-joint safety valve was an important interim step in helping prevent such situations. Downward movement of the string automatically closes the valve, thus offering valuable protection. protection. Additional protection in offshore testing became available with the development of the subsea test tree It incorporates ball valves that automatically, shut in a well when pipe above the test tree is removed or when it parts. With the tree, standard blowout protection is still retained. Sometimes it is protection is still retained. Sometimes it is desirable to run longer-than-normal production or drawdown tests in which wells are allowed to flow for as long as a week. Under such conditions seal wear in slip joints, rams, etc., can become a problem. With the subsea tree, which provides a positive hang-off point for all tubular goods, vertical movement of drillpipe is virtually eliminated except during manipulations needed to open and close the testing tools, and seal wear is reduced.

The recent introduction of an APR safety valve is a significant step in improving formation testing equipment. This tool offers all the benefits of conventional testing and sampling while providing more safety control during operation. It is unique among such tools in that annulus pressure is used to operated the valve.

JPT