Design and Life Cycle Considerations for Unconventional Reservoir Wells

Abstract

Abstract This paper provides an overview of design and life cycle considerations for certain unconventional reservoir wells. An overview of unconventional reservoir definitions is provided. Well design and life cycle considerations are addressed from three aspects including up-front reservoir development, initial well completion, and well life and long-term considerations. Up-front reservoir development issues discussed include well spacing, well orientation, reservoir stress orientations, and tubular metallurgy. Initial well completion issues include maximum treatment pressures and rates, treatment diversion, treatment staging, flowback and clean-up, and dewatering needs. Well life and long-term discussions include liquid loading, corrosion, refracturing and associated fracture reorientation, and the cost of abandonment. These design considerations are evaluated using case studies for five unconventional reservoir types including shale gas (Barnett shale), tight gas (Jonah Field), tight oil (Bakken play), coalbed methane (San Juan basin), and tight heavy oil (Lost Hills Field). In evaluating the life cycle and design of unconventional reservoir wells, "one size" definitely does not fit all and valuable knowledge and a shortening of the learning curve can be achieved for new developments by studying similar, more mature fields. Introduction The emergence of unconventional reservoirs as critical sources of oil and natural gas production has forced engineers and geoscientists to view field development in new ways. One of these areas is the life cycle and design of the individual wells and the upfront considerations that must be taken into account for long-term development. Unconventional reservoirs bring unique problems to such design topics, from well spacing considerations to wellbore orientation, most of which need to be considered before the well is drilled and should be addressed as part of an overall reservoir management plan. When considering the choice of a well type for an unconventional reservoir, one type definitely does not fit all. For instance, the need for a single, small diameter wellbore in a tight gas field is completely opposite of the need for a horizontal wellbore in a shale gas or naturally fractured oil system. Additionally, not only do the constraints of the initial completion need to be considered, but so does the length of the life of the well, which can be considerable in unconventional reservoirs. This paper discusses the design and life cycle considerations for certain unconventional reservoirs. It defines the types of unconventional reservoirs that are addressed and discusses the specific situations that should be considered for such reservoirs. Certain case studies, that demonstrate the need for such considerations, are presented.