f Using Site Survey Data to Monitor Shallow Subsurface Leakage

For many hydrocarbon fields under production there is a chance that operational problems related to<br>production and well completion might cause leakage of hydrocarbons into the subsurface. In some<br>cases a detailed monitoring of such events is desired, and in this paper I suggest to use site survey data<br>to monitor leakage of hydrocarbons into the subsurface formations. In most cases, old site survey data<br>are available, and such data might serve as a base data set. If a second data set is acquired after a<br>leakage event has occurred, it is suggested to use this data set as a conventional 4D monitor survey.<br>There are several limitations related to the proposed strategy, I will discuss some of them in this<br>paper, and then show results from a successful site survey monitoring campaign performed by Saga in<br>1989-1990.