Matrix acidizing treatments was introduced to Hassi 'Rmel field as a mean of restoring and optimizing wells productivity after work-over operations.
If the principle of matrix acidizing appears straightforward, the practice is a mine field of complex decisions. Services companies offers a vast selection of acid systems and diverters. The question that should always be asked before any other is why is the well under producing and then will production increase with matrix acidizing Production may be constricted for a reason other then damage around the borehole.
In the latter half of 1998, a large campaign of matrix acidizing treatments began in the Hassi R'Mel gas field. Well testing results had indicated that many of the wells in the field showed extremely high damage skin factors. In some wells it's approached 200. Despite such severe near wellbore damage, the wells in the Hassi R'Mel field are still capable of producing at very high flow rates due to the extremely good reservoir characteristics. Matrix acidizing was evaluated to be the best option to remove this near wellbore formation damage. The acidizing treatments were performed a six month period by three services companies using different acid system. A unique feature of this series of treatments was that a production logging tool (PLT) was run before, immediately after, and 180 days after the acidizing treatments in every well treated. Somme wells shows good response and others not1 The aim of this work is to answer those questions by selecting the right acid system, in order to restore the production rate, without generating other problems. We tried to find correlation between wells history, pressure analysis and tests laboratory results (core flow tests, XR diffraction mineralogy, fluid-rock compatibility, fluid-fluid compatibility, scanning microscopy) in order to find the way to the right acid design.
Sandstone matrix acidizing long has been used as a means of improving production of oil and gas by removing formation damage and increasing permeability of the zone around the wellbore2.
Laboratory and field studies have demonstrated the effectiveness of this type of treatment In spite of widespread use, however many formations do not respond satisfactorily to conventional HCl/HF treatments. This normally is attributed to rapid spending of HF near the wellbore. Somme wells show good stimulation but later experience an unusually rapid decline in production rate. The decline usually are attributed to plugging by migratory clays and other fines3.
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