Implementation and Intermediate Monitoring Outcomes of the First Commingled Up-Dip SMART Water Injection Well in PA-B Platform Piltun-Astokhskoye Offshore Oil and Gas Field

Abstract

The objective of this article is to share an evaluation of the background, drilling outcomes and production and reservoir pressure impacts from two years of monitoring the first commingled up-dip SMART water injector drilled in the Piltun area of the Piltun-Astokhskoye offshore oil and gas field, located in Sakhalin, far east of Russia. The unique aspect of this water injector is that it was drilled into the up-dip gas caps of two separate reservoirs to provide pressure support to commingled oil producers, complementing the down-dip water injectors already in place. This article highlights some details of the well maturation decisions and expectations based on output of the dynamic modelling studies. Drilling outcomes and well performance is compared to expectations. Initial results of the surveillance programme and field data analysis based on a two-year monitoring period are discussed to show intermediate outcomes of up-dip water injection in the Piltun area. Finally, remaining questions and uncertainties are shared. Piltun-Astokhskoye is a complex multi-reservoir offshore oil and gas field with sizeable gas caps, significant heterogeneity both between and within reservoirs and a complex production history involving commingled oil producers and water injectors. Limited data is available to assess the impact of development decisions. Integrated analysis using multiple data sources and back-to-basics geology and reservoir engineering is required to understand how the reservoirs are responding to up-dip water injection, in order to predict future performance and make informed decisions to optimise the Piltun development over the long term. Surveillance data shows that up-dip water injection is effective in increasing reservoir pressure and oil recovery in one of the reservoirs, whilst having little impact on the other. Analysis shows that variable impact is due to the influence of gas cap size on up-dip water injection efficiency and the risk of trapped gas volumes due to water injection into the gas cap. The importance of integration between different sources of surveillance data and analytical tools to complete a comprehensive and reliable analysis is shown.