Canadian Unconventional Resources and International Petroleum Conference,
19-21 October 2010,
Calgary, Alberta, Canada
To find suitable locations to permanently sequester CO2 is crucially important
for carbon storage. Deep saline formations are thought to be good candidates
for CO2 sequestration due to their large capacity potential. On the other hand,
cases have shown that saline formations can be naturally fractured to some
extent, from small individual fractures to large-scale fracture clusters. Based
on research from various scientific studies, pilot CCS programs and commercial
CCS projects, formations and/or cap rocks with fractures may have significant
Modeling of CO2 flow in fractured systems remains a challenge. In this work,
Discrete Fracture Modeling (DFM) that represents fractures individually and
explicitly is applied to simulate CO2 transport 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 a connection list based simulator.
Several examples, including injection to a formation with or without fractures
and with different hydraulic fracture length, have been simulated based on data
from an actual CCS project.
Results have shown that the existence of mudstone layers could prevent injected
CO2 from leaking outside the reservoir when no fractures are present. While
vertical fractures intersecting with mudstone layers will cause significant
leakage increase as the fractures forms extremely preferential pathways for CO2
transport. On the other hand, if fractures are far enough away from the CO2
plume, it could alleviate dramatic pressure buildup caused by CO2 injection in
the formation and thus help expedite CO2 propagation.
This work presents a systematic way of modeling CO2 sequestration in saline
formations with natural or hydraulic fractures. The main application is to help
improve evaluation and planning of possible CO2 storage location selection to
identify and quantify possible leakage risks through existing or induced
fractures in the injection process.
One of the main concerns for CO2 geological storage is the potential leakage
from the target saline aquifer into other places including the caprock, buffer
aquifers, potable water sources or worstly the atmosphere. Quantification on
each of the above consequences is important to risk evaluation and for decision
makers to propose critical remedies in case of leakage.