Since the late 1990ies Petroleum Development Oman L.L.C. (PDO) is actively exploring for tight gas onshore in the North of the Sultanate of Oman. Recent focus is on exploration targets in clastic formations in the Fahud and Ghaba basins with currently three drilling rigs dedicated to these activities. Most of the wells are deep (TD >5000 m TVDbdf [>16,000 ft TVDbdf]), in H P/HT (High Pressure/High Temperature) environments (even extreme HT >175 o C [350 o F] in some cases, Maldonado et a l. 2006) and need to be stimulated by hydraulic fracturing in several stages for evaluation (with fracture gradients up to 31 kPa/m [1.4 psi/ft]). This paper presents the associated challenges faced for well and completion designs including:  Exploration targets overview.  Uncertainties in reservoir properties.  Selected drilling aspects (well trajectory, casing scheme, cement bond, drill-in fluid, formation evaluation).  Completion design for deep, tight gas exploration wells (tubing sizing, material selection, cemented completions, tubular stress analyses [load case simulations], perforating, other).  Areas for potential future optimization and cost savings.Design experiences gained during the last two years and optimization steps implemented for these deep, tight gas exploration wells will be shared.

For a long time PDO has been suffering from high NPT in some of the Harweel cluster fields located in the south of the Sultanate of Oman, due to drilling through deep high pressure H/C bearings with a narrow heavy MW envelope. Most of these NPTs were due to kick/ loss events, differential sticking, and well control situations. This field is classified as high risk because it has deep HP sour reservoirs. Drilling problems arise in the 8.3/8'' section while drilling through a thick Salt formation that contains floating carbonate bodies. These floaters are normally tight, highly pressurized and small in size. The tolerance window between the pore pressure of the higher pressurized floaters & the formation strength of the relatively lower pressure reservoir is very narrow with respect to the high ECD generated by heavy mud used in these formations. In some cases dynamic losses occur in the lower pressure reservoir while trying to balance the pore pressures of the highly pressurized carbonate body floaters. Mud deterioration due to sour influxes in heavy mud environment sometimes makes the well control situation even more complicated. Managed Pressure Drilling (MPD) technology has been identified as a potential solution for these drilling problems. An MPD trial was conducted successfully in this field which brought huge learning's to PDO. The main achieved KPI in this trial was drilling the troublesome section with MPD system maintaining constant bottom hole pressure. This paper will address the following topics; description of problems encountered while drilling this section, demonstration of how MPD technology is believed to solve these problems and an in-depth description & analysis of the successful trial from the early planning phase to the end, capturing all the learning's for future implementations.