This paper reviews the recently concluded first near balanced nitrified stiff foam drilling application to drill Sui Main Limestone in Sui field Pakistan. The target Sui Main Limestone formation presented numerous drilling challenges in this field. While drilling conventionally total irrecoverable losses were encountered and the resulting loss in head caused the well to kick in. Simultaneously dealing with both these problems resulted in a great amount of NPT, sometimes which extended to a period of months. To address the said problems in an effective and efficient manner, an application of a highly innovative method was considered. Thus a near balanced stiff foam system was designed and found to be highly applicable to drill the Sui Main Limestone formation.

The design of a Near-Balanced Stiff Foam Drilling system (NBD) is first discussed in the paper, which is followed by an overview of the delivered results. While drilling the entire Sui Main Limestone formation no single event of circulation loss was recorded. Also throughout the entire drilling phase "near balanced" conditions were maintained successfully and no influx from the formation was allowed to enter the wellbore. In addition to completing these objectives, another remarkable achievement was that this section was drilled in a record time of 3 days with an average ROP of 14 m/hr while maintaining excellent hole cleaning and no other related drilling problems. In comparison of offset wells where drilling of the same formation would take sometimes up to 3 months, if drilled conventionally.

To sum up, an innovative near balanced stiff foam system was designed to drill the extremely challenging Sui Main Limestone formation. All of the set objectives were delivered to expectations. The operator was able to successfully pass through a cumbersome formation in a record time for this field. This paper elaborates the process used to design a successful near balanced nitrified stiff foam system with applicability for the Sui Main Limestone formation in Sui Field, Baluchistan, Pakistan. The objective of this paper is to highlight all delivered drilling objectives and present lessons learnt while drilling the Sui Main Limestone formation. This will allow for efficient designing of a near balanced stiff foam system for forthcoming wells with similar formations and similar problems.

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