Well construction reliability is always of great importance especially when it is about drilling in an arid region that contains strategic groundwater reserves. This is the case of Hassi Messaoud and satellite oilfields (HMDs) in Algeria where aquifers of the Northern Sahara System (NSAS) Spread out. Problems closely related to well construction such as casing corrosion, cementing lack and also those of post- abandonment are encountered by Sonatrach and partners there.

The main environmental concern becomes, then, how to ensure a reliable and highly safe well design and structure by improving drilling practices and introducing innovative architecture technologies aiming at significantly reducing aquifers contamination risks.

This paper describes how Sonatrach has been able to deal with such problems. Besides, it points out how risks are assessed according to an appropriate method that was fitted for purpose. On the other hand, field data are used to analyze the occurring phenomena and lessons learned from what is considered as the most tragic disaster related to well construction in Algeria - that occurred in Berkaoui satellite field in 1986 -are stressed.

Furthermore, the paper summarizes the steps and the approach taken along the way in stating new drilling performance objectives for HMDs to meet world-class standards and fulfil NSAS protection commitment.

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