The workflows are built under the assumptions that a stringent storage regulation will be in force in all countries. This stringent regulation model is based on the European concept developed in the EU directive21. A license for exploration is supposed to perform all works necessary to confirm the suitability of a preselected area. An authorization for injection test of CO2 is also supposed: we assume that the start-up of facilities construction for industrial injection cannot be granted by relevant authorities without a proper CO2 injection test in the case of DSF project.
Storage exploration is an uncertain and iterative process that depends on many parameters (location and type of target). In this bottom-up approach, we have developed these workflows from first desk assessment of a potential storage to final bankability status, taking into account the possible failures. One of the key issues that these workflows must handle is how such iteration follows a failure (reservoir not found or not suitable in the area, cap rock not found or not suitable in the area). A maximum number of “loops” (re-performance of some works like seismic survey, or well drilling essentially) have been authorized.
The maximum number of loops depends on the suitability of the area (see Figure 17): the lesser the knowledge, the larger the number of loops. This leads ultimately to higher exploration cost.
Whatever the case for DSF, the number of wells required to reach bankability is assumed between two and six. This assumption does not give the number of wells needed for the commercial injection but only the number of wells needed to ensure a storage site is bankable.
The minimum of two wells considers that at least two wells may be necessary to conduct interference tests and to monitor the injection tests. These tests are aimed at gaining sufficient knowledge on the characteristics of the reservoir, cap rock, and upper aquifers22.
The maximum of six wells drilled implies that different “loops” occurred within the workflow. Each loop considers various data acquisitions and re-interpretations. As explained in the following sections, it also implies that a large area is assessed for storage bankability. If the storage bankability has not been reached after all these steps, and considering the significant amount of time and money spent at this stage, we consider the project has failed.
We based our assumptions on similar industries, given the small number of active storage projects worldwide. We extrapolated statistics based onand its shareholders experiences in O&G exploration, underground hydrocarbon storage and geothermal development.
Finally, we supposed that storage projects when deployed after having successfully reached bankability, would inject between 1 and 3 Million tonnes of CO2 per year (Mtpa) for 30 years: each project can be considered as a “100 Mt project”. Bigger projects are considered as a multiplication of such “elementary” projects. The number of workflows necessary to develop a given global storage capacity is considered to stay the same: 100 projects of 100Mt require 100 workflows, and 50 projects of 200Mt also require 100 projects workflows: the workflow must be run on two different locations.
The following list summarizes the main assumptions of these workflows:
- Storage characterization is an iterative process that could be modelled through an iterative workflow.
- Level of knowledge on a geological province has an impact on the time and costs needed to develop a storage project and, therefore, on the development workflows.
- The development workflows depend widely on regulation stringency. A stringent regulation similar to the European one has been supposed for every country. This has an impact on the licensing process and requirements on data collection before getting approval.
- A minimum of two wells and a maximum of six wells will be drilled to determine the bankability of a storage site.
- The success rates refer to technical success ratios in similar industries.
- The workflows were designed for storage sites with a capacity of 100Mt.
The following sections describe the storage development workflows to reach bankability, for the case of deep saline formations (DSF) and depleted oil and gas fields (DOGF), both for onshore and offshore locations.
21 Directive EC31/2009
22 After the characterization phase the monitoring well could be transformed in injection well if the injection strategy requires it.