High-pressure injection of liquids can be challenging in Class I wells where depths exceed 10,000 feet and extreme temperature variations occur between injection and shut-in conditions. Elevated downhole temperatures at these depths create a high-temperature differential between the injectate and annular fluid resulting in significant swings of annulus pressure and surface seal pot volumes. One-way micro tubing leaks at joints have also occurred due to these conditions.
The injectate cools the annular fluid resulting in contraction of the annular liquid and lowering of the seal pot volume, which requires the addition of fluid into the annulus. Once the wells are shut in, annular pressures rise as the annulus fluid is warmed by the native formation fluid, creating an increased pressure differential on the downhole components and increasing the seal pot volume and potentially creating high-pressure situations in the annulus. In addition to the labor-intensive operation of having to add and remove liquid from the annular space, greater downhole pressure differentials may affect long-term integrity of the injection tubing and protective casing.
Maintenance of an annulus pressure that is less than the injection pressure, similar to the operation of more shallow Class I wells, is impractical under the operating scenario for deeper wells. It also creates the potential for fluid migration from the tubing into the annular space in the event of a leak.
Monte Markley, P.G., and Stephanie Hill will present this and more at the 2018 Underground Injection Control (UIC) Conference. The presentation will focus on the design and implementation of an innovative high-pressure annulus monitoring system that mitigates the presence of micro tubing leaks in joints, and pressure and temperature swings of the annulus.
