Challenges in Designing the Optimum Mobility Ratio for Polymer Flooding in Reservoir with High Pour Point Oil: A Case Study from Sago Field Zone-M- Indonesia

Abstract

Sago Structure located in Pelawan District, Riau Province. Sago Structure found in 1940 and began production in August 1940. Sago Structure has active layers of the H, J, K, L layers lies in Tualang Formation and M, N, O, P layers of the Lakat Formation. Currently, the average production wells at Sago Field have an average air content of 98% - 99%, total gross fluid approximately 80,000 BFPD and net oil production between 1,100 - 1200 BOPD. Sago crude oil has the characteristics of HPPO (High Pour Point Oil) with high parrafin content (parrafin content reaches 80% of total weight).
Sago Structure will be applied polymer injection for increasing oil recovery. Polymer injection is one type of enhanced oil recovery (EOR) which is an improvement of the water injection method. It is required to decrease the mobility ratio so as to obtain better areal sweep efficiency and vertical sweep efficiency. One important step in the design of polymer injection is to determine the optimum value of mobility-ratio.
This paper will provide overview of the reservoir aspect before descriptions of mobility control determination and aspects of polymer compatibility with laboratory testing. Based on various criteria of stability of mobility (i.e. mobility ratio), the condition of mobility ratio at Field Sago Zone M indicates instability and there is potential for viscous fingering with mobility ratio value reaches 30. In order to achieve oil stability stability, the target viscosity of polymer solution is 15 cp.
Polymer compatibility tests with reservoir fluid consists of aqueous stability, rheology test by varying polymer concentration, filtration test, screen factor test, thermal stability test, and adsorption test. Polymer samples tested are polyacrylamide type FP3630S, FP5115VHM, Polyflood Max 165, Kypam 6S, Kypam 5SH. Based on the compatibility test, it was found that FP3630S 1000 ppm and Polyflood Max 165 1000 ppm can decrease mobility value and have better viscous stability against thermal and long time condition.