Drilling and Completion Challenges for Deep, Tight Gas Exploration Wells Onshore Northern Oman

Abstract

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.