Abstract

Gas well Groet 1 (GRT1), located onshore in the Netherlands, has been experiencing unstable production for six months since Q1 2002. A down hole video survey identified salt (halite) deposition in the tubing which was subsequently removed by a gauge cutter. The problem reoccurred in Q4 2002 leading to an 8.3 MBOE loss in the quarter. A scale prediction study was conducted to analyse the problem arising with well GRT1 and to diagnose whether the scaling problem is transient or persistent. This study indicated that the scaling behaviour is persistent. Several remedial actions and control options were considered, based upon the diagnosis. All of the remedial actions and control options were compared on a risk / cost / benefit basis. The outcome of this study was that the most economical and lowest risk halite control option was bi-weekly fresh water soaks.

Introduction

GRT1 well was drilled in 1965 and discovered the Groet Rotliegend sandstone dry gas reservoir. Gas production from the field started in 1974 with 4 wells after flowline construction was finished. Initial reservoir pressure was 230 bara at 2100 m TVDss. Reservoir pressure dropped to 36 bara after a cumulative production of 6.1 Bnm3 (December 2003). The field is under volumetric depletion and has shown no indication of active aquifer drive, see the P/Z plot in Figure 1.

GRT1 is now the only active well in the gas field and produces the remaining gas reserves. The other three production wells in the field are shut in due to water coning.

Gas production from the GRT1 well has been stable since start of production in 1974. In April 2002 flow became erratic. A real time down hole video survey identified salt deposition in the tubing at two different levels, see Figure 2 and Figure 5. The liner could not be surveyed because of a salt plug in the tubing end. The salt was removed by a gauge cutter run on slickline and the well performed without any problems for another six months.

The problem reoccurred in Q4 2002 leading to an 8.3 MBOE loss in the quarter. GRT1 well is the only well that produces the remaining reserves of the Groet gas field.

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