Abstract

Determined efforts are being exerted to shore up the integrity of high-pressure high temperature (HPHT) gas wells, which includes studying all observed integrity failures and adjusting practices to prevent potential failures from reoccurring. In high-pressure high-temperature gas wells, casing thermal expansion is a challenge that should be considered in order to maintain the integrity of the well and surface equipment. The objective of the paper is to describe observed growth in a HP gas wells in relation to the wellhead temperature and how it behaves after cycling the well and how it can affect the annuli pressures.

As methodology, two elements varying during shutdowns were studied thoroughly to determine the extent of the impact they may have on the integrity of HP gas wells. These elements are pressure and temperature. While the linear increase of the wellhead growth with increasing temperature was apparent, the subsequent actions of shutting in the well to cool down and then reopening it led to further deterioration of the cement and the wellhead growth increased even further. The engineering solutions and stress analysis at surface facilities is designed to overcome the growth allowance.

The main observation looks at the temperature element and its effect on well integrity in that it analyses the temperature impact on the well’s tubulars and links it to the stresses caused to casing cement and the resulting wellhead growth. Study will also provide recommendations on maintaining well integrity and avoiding any further deterioration. The temperature impact was also observed in one of the wells after it was shut in and wellhead sensors were left to record shut-in wellhead pressure and temperature for about 14 hours. This gave a reasonable indication of how fast it takes for the wellhead to cool down to ambient conditions. In the subject well, the wellhead temperature dropped by 50% in about 2 hours.

As result of the study, in detail reasons for increased wellhead growth in HPHT gas wells and how to avoid it. It also gives recommendations on maintaining well integrity and reducing the impact of full contraction of the well’s tubulars during cooling; such as maintaining wells on constant production, minimizing open and shut-in cycling, and reducing the shut-in time duration.

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