Abstract

Halite precipitation from gas reservoir brines can cause significant decreases in hydrocarbon production or even complete blockage of the well. This has led to many gas wells either producing at diminished rates or being abandoned. Production decline related to halite scale is routinely treated with water washes either in a continuous system or with "mini squeezes" where water is batched in and held for few hours before production resumes usually with increased pressure. Introduction of halite inhibitors as part of the water wash or squeeze treatment has contributed to increased production by reducing the frequency and quantity of water used for treatment.

This paper summarizes the work performed to deliver to the industry a high-temperature, high-performance halite scale inhibitor. The product chemistry offers a true step-change in performance from existing technologies because of its high-temperature stability and halite inhibition efficiency at 420°F (bottom-hole temperature). An industry best-in-class rapid screening technique (kinetic turbidity test) was used to systematically evaluate all current technologies in the market place and to develop a detailed understanding on structure-performance relationships of functional groups. The resulting correlations led to synthesis of novel high-temperature stable chemistries with significantly superior inhibition on halite.

This paper also presents field cases of halite squeeze treatments from two different fields; an ultra hot (420°F) deep (17,460ft) dolomite gas well with severe halite deposition that required water washing every 48-72 hours and a shallow (6,000ft) hot (250°F) shale with erratic production where several water washes, work-overs and varied shut in periods did little to improve production. The ultra hot, deep well case history comes from a field in Texas where a detailed program of work was undertaken that led to squeezing in the halite inhibitor. Halite deposition had forced the operator to reduce production rates, with frequent workover to treat the well mainly with fresh water washes every 48 to 72 hours. After the introduction of the halite inhibitor, the gas well had been continuously producing for 40 days at the first instance and 60 days when the halite inhibitor dosage was increased. This is a marked improvement for the well and saves significant operating cost from well entries and deferred/lost production.

The paper describes a detailed methodology of halite inhibitor selection and the influence that temperature, pressure and salinity has upon application. Field application case histories share important lesson learned with regards to water washing volumes (small and large water washes) as well as the impact of extended shut in period on squeeze lifetime. These squeeze treatments provide valuable field insights to salt formation and prevention in gas wells and the use of the novel high-temperature inhibitor shows a new industry capability of inhibiting halite formation in hot gas well up to 450°F. This was proven by the successful field trials which showed an increase in the gas production at a higher draw-down rate without reducing the tubing/production pressure.

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