AN ANALYTICAL MODEL TO ALLOCATE LAYERED HISTORICAL PRODUCTION DATA TO ENHANCE RESERVOIR MANAGEMENT IN A MATURE WATERFLOOD: THE MINAS FIELD CASE

摘要

Allocating production data among sand layers has always been a problem in managing a multi-layer asset with commingled production. Having a production profile by sand will enhance reservoir management. This study demonstrates that integrating petrophysical and production/completion data into an analytical model is an inexpensive and practical solution to obtain allocated production data by sand layer in Minas Field, Indonesia. The Minas Field has been waterflooded since early 1970's. As technology advancements were made in the area of integrating production and petrophysical data, the opportunity naturally lent itself to Minas. An analytical reservoir model was developed by combining the radial steady-state Darcy equation, material balance, fractional flow concept and Buckley-Leverett Frontal Advance Theory, adopting all associated assumptions. Reliable formation evaluation data are critical for the model. The model analytically simulates waterflooding conditions where reservoir pressure is kept relatively constant and assumes the oil relative permeability profile is responsible for declining oil production. A mechanical skin factor was calculated to represent partial-perforation effects using the Kuchuk-Kirwan formula. Buckley-Leverett was used to estimate post-breakthrough performance. The model runs through 50+ years of completion histories on over 1450 wells. The technique helps to obtain more reliable estimates of production data allocated by sand and also the approximate value of historical average oil saturation by sand. The calculation results were verified by comparing with 36 observed Production Logging Tool (PLT) data. This method has been widely used in Minas and, when combined with diagnostic maps, played a key role in screening and identifying dozens of new candidates. The technique identified the best layers for water injection in the northern area of Minas, which subsequently resulted in a reserves increase of 2.5 MMBO. We believe this technique offers improvements over conventional reservoir flow capacity, kh, techniques and wish to share it for review, comments and suggestions.