The North Field is a major gas field in the Khuff formation, offshore Qatar. Traditionally, this reservoir has been drilled with reduced solids drilling fluids and completed by heavily acidising the payzone in order to maximize production.

The purpose of appraisal well NFS 1-1 was to obtain high-quality representative formation fluid samples from each of the identified producing zones in the Khuff. The detailed gas analysis was required to determine the specifications of the Gas-To-Liquid (GTL) Plant to be constructed to process production from the field.

In order to achieve this, a new testing technique was developed using a ported liner, a high density, low solids reservoir drilling fluid, and a combination enzyme/chelating agent breaker to remove the filter cake prior to testing the individual zones. In order to ensure the success of this challenging operation, a high degree of collaboration between the operator and the supplier of drilling, completion and stimulation fluids was imperative.

The design and engineering of the fluids used during coring, logging, completion and well testing of NFS 1-1 is examined in this paper.

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