As depth increases, so do reservoir pressure and temperature and the mole fraction of carbon dioxide and hydrogen sulfide in the reservoir gas. Furthermore, it is becoming more and more desirable for the operators to produce gas at high flow rates. These factors result in an increase in the corrosiveness of produced fluids and the percentage of wells with corrosion problems. Today, it is estimated that over 50% of the producing gas wells in the U.S. are produced under conditions conducive to corrosion (corrosive wells).
Corrosion costs the petroleum industry more than $900 million annually. This includes production down-time, chemical treatment costs, material replacement costs, and increased workover costs caused by additional fishing time needed to retrieve parted tubing and repair damaged casing. Severe downhole corrosion problems may even force the abandonment of a well and the drilling of a new well.
The objective of this paper is to show that the economic development and production of these wells dictates consideration of three separate but related subjects:
Total optimization of the production system
Limitation of pressure drop through the gravel pack
Consideration of erosional velocity
This study will show that the maximum production rates possible from these wells are usually restricted by the following limiting design parameters (1) pressure drop through the gravel pack (for a gravel packed well) and (2) the erosional velocity. Proper evaluation of these critical areas can extend the life of the production tubing in a corrosive well six to seven-fold.
Although this paper is addressed specifically to corrosive wells, the production optimization techniques shown can be applied to almost any other gas production system.