Casing wear due to pipe body and tool-joint of Range 2 and Range 3 DP is compared using a stiff-string torque & drag & buckling model coupled to a 3D meshed casing wear calculation. Results are compared for multiple well profiles, either smooth or tortuous, in addition to differing pipe-body and tool-joint wear factors.

The Culzean field combines both UHPHT reservoir conditions and an unusually narrow drilling window, at the top of the main reservoir, where reservoir pressure lies on a regional ‘broken seal’ rock strength line. This drove a need to find an improved well architecture, to allow production wells to be drilled close enough to the reservoir crest to maximize gas production volumes. The solution: to develop heavy, ultra-high strength, sour service tubulars and use these in a well layout more typical of Deep Water designs than North Sea HPHT wells. Instead of setting a full production casing string, before drilling the target reservoir, a short production casing liner is hung from the fully rated sour service intermediate string, and tied back after the reservoir section has been drilled and a production liner run. This greatly reduces drilling circulating pressure losses in the reservoir section, allowing crestal targets, whilst providing very robust intermediate and production casing strings for long term well integrity. The reduction in ECD combined with the use of MPD technology, enables the drilling of this complex reservoir, in a safe and efficient manner.

Objectives/Scope This paper will present predicted vs. measured wear for six wells that were analysed in the Culzean field, which is a high-pressure, high-temperature (HPHT) gas condensate field located in the central North Sea. The focus rests on the casing wear prediction, monitoring and analysing process and within that, especially on how to make use of offset data to improve the accuracy of casing wear predictions. Methods The three major inputs to successfully predict casing wear are: Trajectory & Tortuosity, Wear Factor and required rotating operations. All those were calibrated based on field measurements (High-resolution gyro, MFCL (Multi-Finger-Caliper-Log) and automatically recorded rig mechanics data), to improve the prediction quality for the next section and/or well. The simulations were done using an advanced stiff-string model featuring a 3D mesh that distinguishes the influence of different contact type and geometry on the wear groove shape. The "single MFCL interpretation method", in which the wear is measured against the most probable elliptical casing shape and herby allowing wear interpretation with only one MFCL log and avoiding bias error, was applied. (Aichinger, 2016) Results, Observations, Conclusions For the six wells that were analysed the prediction of the largest wear peak per well section was compared to the measurement. In the planning phase (before any survey data was available) the mean error on the wear groove depth was +/− 0.025 [in] (+/− 0.6 [mm]), the maximum error was +/− 0.045 [in] (1.1 [mm]). The average error of the results is summarized in Figure 10 and laid out in detail in Figure 9. Generally, the predictions are accurate enough to be able to manage casing wear effectively. In this particular case, the maximum allowable wear on the intermediate casing was extremely limited to ensure proper well integrity in case of a well full of gas event while drilling an HTHP reservoir. Novel/Additive Information This paper should provide help to Engineers who seek to improve the accuracy of casing wear prediction and hence improve casing wear management. It presents a new way of anticipating tortuosity based on offset well data and it offers a suggestion on how to deal with MFCL measurement error during Wear Factor calibration and Wear prediction.