Opportunity vs Risk : Connected Volume Uncertainty in Highly-Faulted Reservoirs - Case Study and Lesson Learn

Abstract

Subsurface uncertainty will always be part of the field development. Moreover, the existence of multiple faults that divides reservoirs into segments create more challenges and risks in understanding the field performance. In the other hand, this compartmentalized reservoirs typically also offer promising opportunities for undrained or virgin pressure reservoir development which can provide significant added value especially for mature assets. This paper presents valuable case study and lesson learn from Premier Oil Indonesia in modelling and estimating optimization opportunities in highly faulted reservoirs at Garuda Field located in Natuna Sea offshore. Several integrated studies that involved seismic reprocessing, static modelling, fault seal analysis, P/Z Analysis and MatBal simulation were done and lead to identification of several promising opportunities to produce the suspected undrained / high pressure reservoir compartments. However, uncertainty and risk will remain lay underground unless the opportunity is accessed or drilled. Two initial opportunities were drilled and workovered in 2021 that unfortunately had depleted pressure outcome – not align with initial expectation. Case study presented in this paper provide valuable insights and lesson learns in developing compartmentalized reservoirs. Especially when having infill well optimization programs among severely depleted neighbor sands. Despite alignments of several analysis, huge uncertainties are always involved when dealing this type of reservoirs, unless the well is drilled to provide some answers.