Impairment of Gas Well Productivity by Salt Plugging: A Review of Mechanisms, Modeling, Monitoring Methods, and Remediation Techniques

Abstract

Abstract Well productivity decline in mature gas fields, often attributed to liquid loading, may actually be due to salt deposition, which can produce identical symptoms. Salt plugging in gas wells has been well documented in Germany and the USA and is increasingly becoming an issue in the North Sea. There is an increasing awareness amongst North Sea operators of the issue of salt precipitation in gas wells, however, a recent literature search on the subject revealed a limited body of work suitable for use as an introduction to the subject. This paper reviews the mechanisms of salt precipitation, and looks at some modelling and monitoring methods and reviews the available remediation techniques Salt problems occur over a very limited range of producing conditions and are generally seen in mature, depleted gas fields, explaining perhaps the recent increasing interest in the issue amongst North Sea operators (UK and Netherlands). Salt solubility in water decreases with both reducing pressure and temperature, such as in a producing gas well, so that salt can precipitates as saturated produced water flows up the wellbore. The solubility effects are small but are exacerbated, or exceeded, by dehydration effects as produced water enters the wellbore. Salt may precipitate and adhere to the completion walls and produce a salt bridge. Salt can plug perforation tunnels and even form within the reservoir itself. It is not solely a downhole problem, salt precipitation can occur inside surface equipment such as compressors. For production operations, early detection or prediction of salt precipitation is vital, yet it has proved difficult as the issue depends on individual well conditions. The paper discusses how diagnostic modelling may help if certain data are available: produced water salinity, operating conditions along the wellbore and reliable WGR history. Finally, the paper describes current remediation techniques to restore gas well productivity.