Halite Scale Formation in Gas-Producing Wells

Abstract

In Northern German gas reservoirs, the precipitation of salt from the reservoir water is observed to an increasing extent as recovery progresses. The resulting halite scale causes a significant decrease in production rate, all the way to complete blockage of the flow paths and ultimately the abandonment of wells. In order to remove salt deposits as well as prevent the precipitation of salt in the zone immediately surrounding the well, fresh water treatments are performed at regular intervals during production operations. This paper addresses the entrainment of reservoir water from gas reservoirs, even in reservoirs without active edge-water drive, and the halite precipitation in depleted gas wells on the basis of theoretical considerations. The discussion includes a description of chemical parameters determined from analysis of reservoir water for the early detection of salt precipitates in the reservoir rock. Besides the implementation of the fresh water treatment in practice, special attention is paid to the dissolution behaviour of halite scale. The ionic distribution in the back-produced treatment fluid is evaluated with reference to the prevailing reservoir conditions. During the past 17 years, a large number of fresh water stimulations have been conducted in Northern German gas reservoirs. The results of these operations are explained in detail. The success of the stimulation based on the change in productivity index is evaluated and interpreted for parameters such as treatment volume and shut-in time.