Abstract

The paper presents findings of a case history based on the first application of specialized organic fibre lost circulation materials (LCM) in Europe. It lists technical challenges encountered during the recent drilling of HPHT exploration well Stripfing T1 to 6022 mMD and describes how new fibrous organic LCM have proven their value in a range of lost-circulation applications in the Vienna basin. The paper will also elaborate on the narrow mud window available and the main drivers for well design along with contingency concepts.

The operator identified an innovative LCM which had the characteristics that it is plastic, deformable and can be squeezed into a loss zone resulting in an effective seal being formed across the loss zone with an internal filtercake rather than a high loss filtercake forming on the exterior of the wellbore. Several pills containing this product were used achieving excellent results when applied according to a specific procedure. The paper will look in detail at this procedure and highlight the input from detailed decision-tree charts, and the characteristics and wettability of fibres.

The Vienna Basin has a history of mud losses ranging from continuous seepage to severe losses. The main concerns while planning the Stripfing T1 well were the magnitude of overpressure in combination with the expected losses. The above had been the root cause of previous failures.

Several attempts to cure the losses with standard LCM had proven unsuccessful, as a consequence the operator decided to adopt a new approach using a specialized LCM product in order to avoid running casing earlier. Successful implementation of this advanced technique allowed the operator to drill the well using only 3 casing strings and a final hole size of 8 ½ in. without reducing the mud weight.

The level of success achieved by using these materials suggests it should be considered as the preferred standard practice for curing any type and volume of losses.

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