Page 50 - Well Control for Completions and Interventions

Introduction and Well Control Fundamentals 41

Figure 1.17 Hydrate stability curve—Example.

During some interventions, there are circumstances where the co-
mingling of water and gas occurs. These include:
• Integrity testing of pressure control equipment using water.When
performing interventions on a live well, it is standard practice to
pressure test any surface pressure control equipment, such as a wire-
line lubricator or coiled tubing stripper. These tests are normally
conducted using water. On completion of the test, the valves in the
Christmas tree are opened to give access to the well. In most wells,
including those producing liquids, there will be a gas cap at the sur-
face. Water falling from the surface as the tree valves are opened
will mixwiththe gas. Ahydrate canformifthe pressure and
temperature are in the hydrate zone.
• Production start-up of cold wells. Wells that produce water are particularly
vulnerable. Consider a situation where a well has been closed-in and
water remains in the low-lying sections of the flowline. During the
shut-in, gas accumulates below the closed tree valves. When the well
is opened, gas comes into immediate contact with water in the flow-
line. Similarly, a newly perforated well can be vulnerable if it was filled
with water when perforated. As production starts, gas migrating up
through the water can lead to the formation of hydrates at the surface.