Addressing the Challenges of Hydraulic Fracturing Vertical Wells in Differential Depleted Tight Gas Accumulations in Oman

Abstract

Hydraulic fracturing has been a key technology enabler for the development of tight gas formations in Oman. This tight gas accumulation has been developed with the supported of vertical wells, fractured at different depth covering up to 10 different hydrocarbons units. The intrinsic geomechanical, petrophysical and lithological heterogeneities of this tight units impact not only the fracture conductivity distribution but the drainage efficiency of the fractured zones, this is observed as mobility variations across this unit impact their contributions once all become commingle, with the areas of higher mobility dominating the total gas well production. It was anticipated that depletion of the higher mobility units will impact and change the contribution dynamics of the commingle production. However, this is only one dimension of the challenges to be considered as part of the hydraulic fracture strategy during the field development. This paper will be focus key operational challenges and the fundamental formation characterization requirements to assess in-situ stress dynamic variations during the life of the field; incorporating formation pressure points as integral part of the drilling program and in-situ stress measurements supported by wellbore stability evaluation and mini-fracture operations. It will be presented how variations on pressure and stress profiles, as the field developed, will impact the perforation and fracture strategies as well as pressure operating envelop to assure well integrity. It will be described the logging requirements as well as the lab characterization needed to determine key elastic properties to assess the hydraulic requirements for fracturing individual units or combination of them. It will be discussed how increase of pressure confinement potentially affects the in-situ elastic properties as depletion is experienced on specific gas units, inducing alterations on stress profiles that impact fracture propagation and final conductivity distribution. The use of radioactive tracers in combination with production logging were implemented to assess containment and fracture prediction, providing this an essential tool to determine fracture propagation behavior, deployment strategy and final conductivity distribution. Key operations covering plug milling, post fracture clean out and well lifting will be also discussed. Finally, it will presented key observation that can be implemented as part of methodologies used for fracture deployment on differential depletion formation, this leading to optimum field development while maximize investment.