Best Practices for High-Temperature Gas Well Abandonment Plugs

Abstract

Abstract Wellbore abandonment in high-pressure, high-temperature (HPHT) wells is an exceptionally challenging operation in the drilling phase because it must satisfy the abandonment criteria but also must ensure that the placement and pullout of the cement plug occurs without obstructions. In this paper we aim to detail the best practices acquired for placing cement plugs under such well conditions. Our methods cover both slurry design and placement practices. Instead of having multiple diameter shifts, the placement pipe was selected to minimize contamination. Best practices for plug pull out of hole (POOH) included calibrating the openhole diameter to ensure the displacement was accurate. For the fluid designs, not only were density and fraction hierarchies followed, but the important step was ensuring fluid compatibility in downhole conditions. Being a gas well and with exposed flow zones in the open hole, the plug had to be designed as gas tight. HPHT gas-tight cement must present stability at HPHT downhole conditions to prevent any potential settling or free fluid that can compromise its performance. Fluid loss and thickening time properties are tailored accordingly, with tight fluid loss control below 50 mL/30 min API and enough safety margin for a challenging environment. The cement spacer also is a crucial fluid in the cement plug placement to prevent contamination of the cement slurry and provide the proper density and rheology hierarchy for mud displacement but is easy to be displaced by the cement slurry. Many of the design inputs were verified with execution. First, the POOH fluid levels indicated the caliper assumptions were correct. This was further verified with the returns data post-job circulation. The cement tag after wait on cement (WOC) assured us of the contamination simulation outputs, as the cement was tagged on the desired depth and the well was stable. We will cover the details of additives and simulations that aided in ensuring the HPHT cement plug design met objectives. By applying the entailed best practices, this execution was the first successful abandonment for a deep gas well for the Amin Formation in Block 60.