Lean HC gas injection pilots analysis and IPR back calculation to examine the impact of asphaltene deposition on flow performance

Abstract

Gas injection is one of the most economical and effective approach to improve oil recovery. However, outcome of such approach is contingent to reservoir heterogeneities impacting gas override and fingering. Furthermore, injected fluid composition and its compatibility with the reservoir fluid potentially impact flow assurance issues such as asphaltene precipitation into the wellbore and surface facilities.The objective of this paper is to examine the lesson learnt from a couple of field scale 5 spot patterned lean hydrocarbon gas injection pilots which were deployed in a heterogeneous carbonate formation of a giant field located offshore Abu Dhabi under secondary and tertiary drive mechanisms. Said pilots provides a valuable insight on production performance, pressure support, gravity override, fluid composition and evidence of asphaltene deposition that resulted in heavy production loss prior to the solvent treatment.This paper presents the overall pilot performance including pattern recovery, fluid front movement, potential role of heterogeneity in gas breakthrough timings and the operational events to witness asphaltene deposition affecting the flow performance. The deposited asphaltene cake thickness was measured mechanically during routine tubing clearance check operation that was helpful in estimating production loss due to altered production tubing flow opening. Also an integrated approach is applied to confirm the AOP laboratory measurements with the actual deposits of asphaltene that were found in to the production tubing.In order to confirm the effect of asphaltene deposition on inflow from near wellbore formation to the wellbore, a straightforward yet innovative nodal analysis approach was applied to study well performance using the calibrated and history matched well model. It was noticed that not only the outflow was altered because of asphaltene deposition into wellbore but also the inflow (productivity index) was seriously impacted potentially due to asphaltene deposition in near wellbore formation.