CASE STUDY: Tubular Design

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High Pressure High Temperature Well Casing Design, Annular Pressure Buildup Study, and Wellhead Movement and Loading Analysis for Drill-Stem Test, Offshore Israel

CHALLENGE

The client needed to verify the high pressure high temperature well architec-ture according to their latest design guidelines. Further analysis was required to assess the wellhead movement during the hottest drill-stem test (DST) event to enable drill-stem space-out inside the blowout preventer (BOP) and, for the same event, to assess the way the annular pressure buildup effect would impact the adjacent casing strings and liners.

The well architecture was comprised of multiple casing strings and over-lapping liners hanging off at both the surface and the mudline. To perform a thorough single-string stress analysis on all casing strings and liners, all significant drilling operations needed to be modeled to obtain the most realistic casing and annuli initial thermal profiles. Next, according to the well test program, all relevant DST operations were simulated to obtain the final thermal profile needed for the loading conditions and annular pressure buildup calculations. A single-string stress analysis was performed according to the company’s specific casing design guidelines and based on the drilling and production test thermal analysis. The modeled load cases covered the entire casing’s operating envelope to account for all anticipated loads which, occurred during the life of the well. Then, the annular pressure buildup was calculated for all annuli, and the adjacent casing strings and liners were checked for integrity. During the high case, DST production operation (highest temperatures), the well system (comprising of all casing strings hung off at wellhead and at mudline) started to move in response to the strings’ thermal expansion, causing the space-out of the drill-stem inside the BOP to change. To quantify this movement, a wellhead movement analysis was carried out, so that it was compensated by moving the test string along with the BOP and wellhead.

SOLUTION

RESULTS

Performing these calculations enabled the operator to assess whether the casings and liners keep their structural integrity during drilling and DST operations, provided the safe operating envelope of all casing and liners, and helped to minimize and timely mitigate the risk of a failure, which could have led to a negative environmental and economic impact. The wellhead movement analysis enabled an accurate string space-out inside the BOP so that in the event of a well control situation, the BOP rams would close around the test string.