Technical Paper: Formation Testing, Completion Integrity Evaluation and Geomechanical Applications using a Wireline Cased-Hole Formation Tester

Society: SPE
Paper Number: 125106
Presentation Date: 2009
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Wireline formation testing is traditionally carried out in open-hole wells. Advances in formation tester technology have provided the industry with a new modular cased-hole formation tester (CHFT). In this new design a hole is drilled through the casing and cement, communication with the formation is then established enabling formation testing and sampling. The drilled hole is subsequently plugged.

This paper describes several case-studies from the North Sea where a full range of formation testing applications (that would traditionally be performed in open-hole) were made in casing using a cased-hole formation tester. In addition to pressure testing and sampling, three recent case studies demonstrate advanced applications.

The first example demonstrates zonal isolation behind casing and identifies communication between layers under injection. The reservoir consisted of two layers with significant permeability contrast. The CHFT was set at the bottom of the higher permeability zone and a hole was drilled thought the casing and annulus. The pressure was monitored while seawater was injected at increasing pressure steps into the lower permeabily zone. By analyzing the pressure response the degree of zonal communication and the maximum injection-rate were obtained.

In the second example, the CHFT was used to determine whether production wells could be drilled safely, and to evaluate bypassed reservoir layers. A very deep and deviated injection well completed and perforated over a long interval was tested with a CHFT deployed by tractor. Formation testing results provided a formation pressure profile in un-developed zones and showed that the injected interval was over-pressured and above the maximum safe pressure for drilling operations.

The final case study described in this paper shows an application of the CHFT for shale integrity testing. A poor cementing operation potentially left a production well without zonal isolation. The overburden shales are weak and prone to collapse. If the quality of the seal provided by the collapsed shale is tested for integrity and can be qualified as a barrier providing zonal isolation, the operator could avoid the expense of drilling a side-track. Two effective-stress testing cycles were made with the CHFT, which confirmed the integrity of the shale barrier, and quantified the minimum horizontal stress.

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