As rig time and completion costs continue to rise, it is increasingly important that reliable reservoir data be gathered rapidly, economically, and safely. A properly conducted Formation Test or Drill Stem Test will provide the reliable reservoir data. Todays technology has made available safe and dependable equipment for testing offshore both from platforms and floating vessels. Equipment such as quick closing remotely operated surface valves, down-hole safety valves, and down-hole pressure responsive tools are now available for safely obtaining adequate reservoir data. Criteria for the equipment was established to promote safety, dependability, and compatibility with existing equipment. The criteria for testing from floating vessels was that the equipment must provide:
A safe system for testing incorporating multiple back-up equipment.
Minimum amount of ‘rig-up’ time, on the well. Properly run Formation and equipment.
Remotely controlled surface equipment.
Down-hole safety valves that would close automatically, or intentionally, when required.
Minimum amount of rotation during the test.
"Hang-off" points at ocean floor to prevent down-hole drill pipe movement during the test.
An optional means to trap a sample at final flow pressure and bring it to the surface for analysis.
Obtaining meaningful reservoir data safely by Formation Testing is an economical necessity today. The time to evaluate a reservoir is when a minimum amount of permanent expenditures has been made on the well. Properly run Formation Tests, i.e., two equal flow periods of sufficient duration to clean up the well and to establish a flow rate, each followed by a closed-in-pressure period long enough to provide a minimum of 65% closure of the closed-in-pressure curve, should provide adequate reservoir data, including reservoir extent. Character of each individual well should dictate the times allocated the flaw and closed-in-pressure periods. Experienced personnel on location are in the best position to evaluate formation behavior patterns, and thus adjust the time periods for the test. A big savings in rig time is possible when time periods are properly chosen. Unnecessarily long closed-in-periods, for example, could be eliminated by an experienced well-site judgment. Conversely, proper well-site judgment can assure you that adequate flows and closed-in-pressure times are obtained.
Safety of personnel equipment, and the ecology must also enter into theeconomical realm. Technology has moved safe offshore testing into the era of practically. Tools to help protect man, equipment, and ecology', are available and wilI be discussed in the following paragraphs.
In mid-1968, increased deep water orilling from floating vessels coupled with ecologicaI concern, fostered development of a new technique of Formation Testing. Criteria for this technique envisioned a progressive development of equipment starting simply and continuing today with a completely new concept in Formation Testing tool operation.
A review of the criteria used in developing the equipment for testing offshore can best point out the technological advancements made in the last three years. Criteria for testing from floating vessels was that the equipment must provide:
A safe system for testing, incorpc, rating multiple back-up equipment.