Green Canyon development wells are perforated and tested using the IMPULSE* testing method before completion or recompletion. This method allows a controlled underbalance stimulation of unconsolidated formations so that an initial reservoir pressure and reservoir data can be obtained. A pressure pulse controlled drill stem test (DST) system is used to carry out these well testing operations.
This new DST control concept overcomes some of the limitations of conventional DST tools; equipment reliability is increased in difficult well conditions. This new system has improved the efficiency and safety of well testing in this area.
Conventional DST strings require mechanical pipe manipulations and/or increasing levels of pipe manipulations and/or increasing levels of annulus or pipe pressure to actuate sequentially the tools in the DST string during the different test phases. These operations can become difficult, time consuming or limited under certain conditions for the following reasons:
The control of DST tools through pipe manipulation is difficult to monitor indeviated wells because of pipe drag inside the casing and on offshore floaters because of rig movement with the heave; this difficulty in controlling the string may jeopardize the operation with unwanted situations such as an unseated packer.
Pipe manipulations are dangerous when operating with differential pressure between the pipe and the annulus; this is the case during underbalanced perforating.
Conventional DST tools operated by pressure can only be actuated in the sequence planned during the design of the test, no deviation from this preset sequence is allowed once the tool string is in the hole. Excessive pressure may jeopardize well safety with, for example, a burst casing or a collapsed tool; the number of increasing sequential pressure levels to be applied to the annulus to operate the different tools in the string is therefore limited. The problem is worse when perforating a deviated well since a pressure actuated tubing conveyed perforating (TCP) firing system is normally preferred to a drop bar system. In a workover situation, where an inplace casing must be protected because of questionable integrity, the maximum pressure that can be applied to the annulus can be quickly reached.
Finally, severe sand production during the flow period of a test affects the correct mechanical operation of conventional DST tools.