A Risk Based Management Approach to the Problem of Gas Migration

Abstract

Gas migration, i.e. the leakage of gas outside the wellbores of oil and gas wells has been recognized for many years as a problem but is still not clearly understood. It can exhibit itself as gas pressure on the surface casing, gas migrating through the soil around the wellbore, or both. While it is probable that it occurs in other regions, the phenomenon is particularly visible in the Lloydminster area of Alberta and Saskatchewan, in part because of the high well density, as well as the fact that much of the land is under cultivation, which makes the effects on vegetation more evident. There are, as of yet, no technologies which can consistently demonstrate success in meeting the existing regulatory standards, which dictate zero tolerance. Based on the available data it is estimated that it could cost hundreds of millions of dollars to eliminate the problem. Research and development work is underway to assess the risks and impacts of gas migration on soil, the atmosphere and groundwater, as well as to improve technologies to eliminate, reduce or mitigate the problem with the ultimate goal of developing a risk-based management approach. While the problem is technically complex and the costs of meeting zero tolerance standards may be extremely high, initial research results indicate that the risks and impacts associated with gas migration, generally speaking, appear to be low. This paper will give an overview of the problem and an update of the work which has been done, with particular emphasis on on-going work to assess gas migration through groundwater aquifers. The results of measurements of methane around leaking wellbores and the conclusions which may be drawn from the data will be described.