Integrating 4D Data Into Dynamic Model Improves Johan Sverdrup Field Development

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 209541, “Integration of Johan Sverdrup PRM 4D Data Into the Dynamic Model,” by Monica A. Calvert, Yuri Tsaplin, and Hans P. Hansen, TotalEnergies. The paper has not been peer reviewed. _ The Johan Sverdrup field permanent reservoir monitoring (PRM) system now has recorded two surveys documenting the progression of the waterflood since production and injection began in October 2019, revealing a clear 4D signal linked to the increase in water saturation. The 4D signals have been used to help guide updates within the reservoir model, providing a better understanding of how the field development is progressing. Field Background and PRM System The giant Johan Sverdrup oil field was discovered in 2010 in the North Sea approximately 150 km west of Stavanger. The field is laterally extensive, covering 200 km2 and consisting primarily of Upper Jurassic intra-Draupne sandstone and Upper Triassic-Lower Jurassic Statfjord sandstones in a low relief structure. The reservoir is characterized by excellent porosity and permeability, with drillstem tests showing permeabilities of up to 70 darcies with good communication over long distances and across faults. The oil is undersaturated with a low gas/oil ratio and is normally pressured, with slight depletion from a regional drawdown. Reservoir thickness varies across the field, with the intra-Draupne sandstone ranging from 5 to 40 m. The primary drainage strategy includes initial waterflooding to be supplemented by water-alternating-gas injection at the end of the oil-production plateau. The full field development consists of 64 wells, both platform and subsea. Producers are placed on the structural highs with water injectors placed on the flanks below the initial oil/water contact (OWC). Because of full voidage replacement by water injection, reservoir pressure is expected to stay fairly constant during field life. Johan Sverdrup is the first oil field to have a PRM system installed before production startup. The PRM system is a key component of the reservoir-monitoring and data-acquisition plan and was installed in two stages in 2019 and 2020 (Fig. 1). Yearly monitor surveys are planned to monitor waterflood development. The first seismic acquisition in 2019, referred to as PRM0, covered the initial first stage of installation on the northern part of the field. Stage two of the installation was completed in 2020, and two monitor surveys have since been acquired, covering the entire field, in 2020 (PRM1) and 2021 (PRM2). Feasibility studies show that a 4D response would be detectable within the reservoir. The increase in water saturation caused by water injection and upward movement of the OWC yields an increase in acoustic impedance, or hardening, in the reservoir. For the 4D analysis, the main seismic surfaces used were the Top Aasgard formation, the Top Viking group (which contains the Draupne formation), and the Intra Upper Triassic Unconformity (IUTU). The acoustic impedance increase measured in the 4D seismic data is compared with water-saturation changes within the reservoir model. Differences between the two can highlight areas within the reservoir model that require updating.