The name "Sui" has become synonymous with natural gas in Pakistan. Located at a distance of about 650 kilometers (km) from Karachi in Balochistan Province, Sui is Pakistan Petroleum Limited’s (PPL) flagship gas field. The gas field was discovered in the late 1952 and the commercial exploitation of the field began in 1955.

Two major reservoirs of this field are Sui Main Limestone (SML) & Sui Upper Limestone (SUL); both have become highly depleted over the time. Conventional drilling technologies in these formations result in complete loss of drilling fluid, stuck pipe & severe formation damage.

Pakistan Petroleum Limited (PPL) planned drilling Sui93(M) as a horizontal well in Sui Main Limestone (SML) Formation. Drilling a horizontal well with conventional drilling technology in a depleted formation having 500 psi pore pressure at a depth of ~1400 m (TVD) was a real challenge. Underbalanced Drilling Technology (with DDV & ER-EM-MWD tools) was selected as an alternative drilling method. The main objectives of Underbalance Drilling Operation were to drill to target depth while eliminating fluid losses with associated problems and improve drilling performance.

A multidisciplinary team of Drilling Operations experts planned and executed this challenging project. Considering the reservoir pressure of formation, stable foam was selected as drilling fluid for UBD operations. Extended Range Electromagnetic MWD tool was used for directional control along with APWD (Annular Pressure while drilling) sensor for real time Bottom Hole Pressure monitoring. Open hole section (~600 meter) was drilled successfully in Sui Main Limestone (SML) Formation.

Integrated efforts of Pakistan Petroleum Limited (PPL) and associated service companies of various disciplines during planning and operation phases of the well led to this successful project.

This paper highlights key factors in the underbalanced drilling design phase, operational challenges faced during execution and results of the first well drilled in Middle East region using above mentioned integrated group of technologies. These applications have opened new ventures and opportunities for depleted field developments in the region and particularly in Sui Field of Pakistan.

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