Exploration and development of Heavy oil fields with high water cut and sand production in Muglad basin in Nothern Africa started with vertical wells and as time progressed matured into drilling Horizontal wells.

Typically drilling challenges in this area include drilling very reactive shales, shallow kick off depths and high build rates, unconsolidated sand stones interbedded with shales which are sensitive to mud weight and are prone to lost circulation.

First few horizontal wells were drilled with conventional technology of positive displacement motor with silicate mud. Many of these wells faced hole cleaning issues leading to pack off, excessive back reaming and stuck pipe incidences. Uneven build rates via sliding in interbedded formation leading to high borehole tortuosity. It is significant to note that due to these difficulties one of the planned horizontal wells was side tracked three times after stuck pipe incidences and finally completed as a 30 degree deviated well with a total cost over run of 300% above AFE.

Since then Rotary steerable system has been deployed to drill these challenging wells with significant improvement in drilling performance, saving days and cost and eliminating stuck pipe incidences. This paper compares the performances of drilling with PDM Vs RSS in the same reservoir and presents the lessons learnt. A cost benefit analysis has also been performed and it clearly shows that RSS is both technically and economically a sound approach to drilling horizontal wells in Muglad basin.

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