Numerical Simulation on CO₂ Leakage through Fractures along Wells Using Discrete Fracture Modeling

The first and foremost task for carbon storage is to find proper locations to permanently store CO₂ which are injected into deep saline aquifers. However, fractures in the reservoir as well as channels along the wells form preferential pathways for CO₂ transport to make it easily escapes from the reservoir. Various scientific studies, pilot CCS programs and commercial CCS projects have shown that leakage problems will be detrimental to the environment and safety to human race.

Modeling CO₂ flow in fractures along the well remains a challenge. In this work, several CO₂ pathways are characterized, including fractures in cement, casing and the rock. Discrete Fracture Modeling (DFM), which represents fractures individually and explicitly, is applied to simulate CO₂ movement in a saline aquifer. This requires unstructured gridding of the saline formation using Delaunay triangulation and transmissibility evaluation between each pair of adjacent cells. Simulations have been done using General Purpose Reservoir Simulator with a non-neighbor connection list.

Several examples including flows through wellbore failures, sloped layers as well as Hydraulic fractures are presented. Through the simulation results, it is found that near well fractures act as extremely preferential flow paths for CO₂ transport. Fracturing would help CO₂ retained in the target aquifer.

The main application of the framework presented in this paper is to help those involved in evaluation and planning of possible CO₂ storage location selection to identify and quantify possible leakage risks through drilling and completion induced fractures.