Improving ultimate recovery in the Granite Point field Tyonek C sands

Abstract

The objective of this research is to determine how the ultimate recovery of the Granite Point field can be improved. An understanding of the depositional setting, structure, stratigraphy, reservoir rock properties, reservoir fluids, aquifer, and development history of the Granite Point field was compiled. This was then leveraged to provide recommendations on how the ultimate recovery can be improved. The Granite Point field Tyonek C sands are located on an anticline structure at 8,000' to 11,000' SSTVD within the offshore Cook Inlet basin. These sands were deposited in a fluvial environment with the source material provided by the Alaska Range to the northwest. Due to uplifting, the Tyonek C sands are of relatively low porosity for their depth. The sands thin, become more numerous, and are of generally lower porosity from southwest to northeast. Oil quality is excellent and displacement efficiency of the reservoir rock with water flood exceeds 50% at breakthrough. Although displacement efficiency is high, the relative permeability to water is extremely low. The fracture gradient of the reservoir rock is on the order of magnitude of 1.0 psi/ft. Many initiatives were undertaken throughout the history of the Granite Point field to improve the rate and resource recovery, all of which were met with negligible success with the exception being the introduction of horizontal wells that were first drilled in the early 1990's. The underlying reason for the lack of success of these other initiatives is the low effective permeability to oil and the extremely low effective permeability to water. Secondary recovery with water injection was successful in the early stage of development, and can be in the future, but only when applied between wells that are connected by a sand of acceptable porosity. The results of this research indicate that to improve the ultimate recovery of the Granite Point field a thorough quantification of aquifer and injection water movement must first be understood, then horizontal wells can be placed in appropriate locations to improve the offtake and leverage the weak aquifer drive to provide pressure support.