Underbalanced Drilling (UBD) is becoming more widely used and accepted because of the many benefits it provides such as:

  • Limitations to the formation damage common in regular overbalanced drilling.

  • Increased rates of penetration.

  • Increased production rates and in some cases production while drilling which can provide early cash flow and enhance economics.

However with these advantages come some drawbacks, the chief among which is the safety of the operation while tripping the drill pipe into and out of the well.

Since the well is allowed to flow in traditional UBD operations a flowing or shut in pressure results in the well. Any significant pressure at surface requires that special precautions be taken during tripping operations to control formation pressure. Several techniques can be used among which are:

  • Killing the well, this provides for safe tripping but can obviate the very reason for using UBD - formation damage can result.

  • Flowing the well, this can lead to a dangerous situation if a sloughing formation forms a temporary bridge in the annulus.

  • A Snubbing unit can be employed, this enhances safety but can add considerably to the operational cost.

It is clear that a better and safer method is needed, since all the above carry disadvantages, and to this end a new method involving a downhole valve was conceived. In this approach a full opening valve which can be closed below the drill string while tripping, is deployed downhole below the "pipe light" depth and operated from surface by way of a hydraulic control bundle.

This paper will review the concept of the Downhole Deployment Valve (DDV), its design and operation. The authors will go on to provide details of the first field trial of the a 7" 26lbs/ft full opening valve in a multilateral well which was drilled underbalanced in the James Lime play in East Texas/Northwest Louisiana. They will conclude that this device can provide major enhancement to a UBD operation without in any way compromising its advantages.

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