Well integrity assessment under temperature and pressure stresses by a 1:1 scale wellbore experiment

Abstract

A new in situ experiment is proposed for observing and understanding well integrity evolution, potentially due to changes that could occur during a well lifetime. The focus is put on temperature and pressure stresses. A small section of a well is reproduced at scale 1:1 in the Opalinus Clay formation, representative of a low permeable caprock formation (in Mont Terri Underground Rock Laboratory, Switzerland). The well-system behavior is characterized over time both by performing hydro-tests to quantify the hydraulic properties of the well and their evolution, and sampling the fluids to monitor the chemical composition and its changes. This paper presents the well integrity assessment under different imposed temperature (17-528C) and pressure (10-28 bar) conditions. The results obtained in this study confirm the ability of the chosen design and observation scale to estimate the evolution of the well integrity over time, the characteristics of the flow along the well-system and the reasons of the observed evolution. In particular, the estimated effective well permeability is higher than cement or caprock intrinsic permeability, which suggest preferential flow pathways at interfaces especially at the very beginning of the experiment; the significant variations of the effective well permeability observed after setting pressure and temperature stresses indicate that operations could influence well integrity in similar proportions than the cementing process.

Well integrity assessment by a 1:1 scale wellbore experiment: Exposition to dissolved CO 2 and overcoring

“…In our case, the migration along the well seems to have occurred mainly along the clay/cement interface. The increase of temperature at the bottom of the well has closed that interface progressively but the interpretation made after the first year of experiment (see Manceau et al, 2015) and the observations made during and after the overcoring indicate that a micro-annulus was still present at the top of the well. It can be assumed that this micro-annulus was present at the very beginning of the experiment all along the well to explain the initial permeability of the well (20 mD), despite the care taken to perform the cementing.…”

“…In this section, we recap essential information for understanding stage B. For an extensive description of the experimental concept and of stage A, the reader is referred to Manceau et al (2015).…”

“…For stage B, the effective well permeability has been determined based on the same inverse modelling procedure than that used for stage A and presented in Manceau et al (2015). A 2Dradial numerical model has been developed using TOUGH2 code (Pruess et al, 1999).…”

“…This experiment has been designed to evaluate the sealing behaviour of a well after mechanical and chemical stresses due to pressure and temperature changes (stage A) and due to the exposure to carbonated brine (stage B). The stage A has been the subject of a first publication (Manceau et al, 2015) and the stage B is described in this paper. The paper also presents the outcomes of the overcoring procedure (similar procedures have already been carried out in other contexts, e.g.…”

Experimental Modelling of the Caprock/Cement Interface Behaviour under CO2 Storage Conditions: Effect of Water and Supercritical CO2 from a Cathodoluminescence Study

“…Samples of cement are aged under high CO 2 pressure and at different temperatures. Some studies focus on cement/rock interfaces, with the rock being sandstones (e.g., [9][10][11] Cao, Walsh, Mito), basalts (e.g., [12] Jung), shales (e.g., [4,13]), siltstones (e.g., [14] Newell), or claystones (e.g., [15] Manceau).…”