Effective Containment Pressure – A Concept for Casing Shoe Strength Assessment and a Method for Forecasting It

Abstract

The method of selecting casing shoe depths has historically been based on a number of concepts, including Fracture Gradient prediction, Overburden Pressure assessment and Kick Tolerance allowance. These methods do not take into account the fractured, permeable and faulted nature of geothermal reservoirs, and thus in some instances can be a poor model. The most recent iteration of the New Zealand Code for Deep Geothermal Wells (NZS2403:2015) introduced more geothermally-appropriate concept of Effective Containment Pressure (ECP) which can better account for a vagaries seen in geothermal reservoirs. In well operations and planning, Contact Energy adopted a method for assessing ECP to use as a forecasting and predictive tool for both well construction and setting operating limits on existing wells.