oa Trace Origin of Gas Leakage behind Casing Using Stable Isotope Geochemistry

The combination of carbon (δ13C) and hydrogen (δD) isotope analysis of natural gas is a very powerful tool to discriminate different origin of natural gases. The technique is based on the assertion that the isotope composition of a natural gas is not always the same. This paper is describing the first application of stable isotope geochemistry in Qatar Petroleum to determine the composition and source of gas found in the well annulus in which no gas should be present. Tracing the origin of gas leaking behind casing has a great impact on well integrity.

In the frame of this study three gas samples collected in duplicate from the production tubing, annulus 1 (A1) and annulus 2 (A2). The main objective of the study was to determine if the gas in the (A2) has a similar or different composition than the injected and produced gas in the (A1) and tubing.

The preliminary conclusionsare:

• Gas from A1 and tubing are of similar composition and therefore have a similar origin
• Gas from A2 id of different composition than A1 and tubing gas and therefore is of a different origin
• Presence of Hydrogen in A2 gas is most likely attributed to corroding metal from well casing