Assessing the Value of Reservoir Surveillance Data from Gas Fields Producing to LNG Plants Using VoI (the Value of Information)

Abstract

A set of examples will be shared for calculating the value of reservoir surveillance conducted in gas fields tying into LNG plants. This includes such measurements as transient pressure, rate and temperature changes, fluid chemistry or diagnostic information related to well integrity. These data are typically gathered during production operations, but their value is rarely quantified. The objective of this paper is to use existing VoI methods to provide a means to justify this reservoir surveillance. The results will be useful for justifying routine surveillance activities to other departments in the upstream organisation, e.g. Operations and Facilities Engineering. Established VoI methods will be applied to common surveillance problems occurring in production operations. In operating fields, gauges and metering equipment are already installed so there is no additional cost. However, surveillance may incur either personnel labour costs (when wells are still flowing) or lost production caused by shutting in wells (e.g. pressure transient tests). This is compared against the calculated value of a more reliable production forecast incorporating the new surveillance data. This value is realised when the future supply to a gas plant is ensured – i.e. avoiding future ullage or penalties from missed cargo deliveries. Discussion is provided on the degree of uncertainty for which interpreted production data (pressure, rate flow and time) resolves reservoir parameters and forecasting metrics. This is known as imperfect information. It is concluded that VoI is a powerful method with application in two areas. Firstly, it can be used in daily reservoir management and to increase production forecast reliability. Secondly, the surveillance data are used to inform future decisions such as infill drilling or compression projects (gas plant ullage). It is observed that management of operating companies are more inclined to agree to reservoir surveillance when its value is clearly calculated. Several generic and non-specific case studies are given that could be applied to gas fields on the North West Shelf in Australia. Most commonly, the VoI method is used prior to field development during the appraisal stage. The main difference for operating fields is that there are usually minimal material/service costs for these tests, but the cost relates to foregone production when the well is offline or curtailed. Few papers, if any, discuss its application to producing wells. However, in the upstream organisation the question of the value of surveillance arises and should be addressed.