Offshore Large Scale Polymer Flood Implementation at Chengdao Field

Abstract

The number of polymer injection projects has greatly increased worldwide in the past decade, with more and more full-field implementations. More recently, the focus has shifted towards deploying such technologies offshore, which presents specific constraints regarding facilities, logistics, or even produced water treatment. Polymer flooding is an EOR technique that has been widely implemented in China. The oil & gas company SINOPEC has gained extensive experience with polymer while developing the Shengli oil fields. The implementation of polymer flooding in the Chengdao offshore oil field was sanctioned in 2019. This large-scale project has seen polymer injection in 43 wells since October 2020. Polymer flooding helps increase oil production and accelerate recovery by providing a better sweep efficiency as a tertiary oil recovery method. It also results in unique environmental benefits with a reduction in CO2 emissions by 52 to 64% per produced barrel of oil. This project consists in injecting polymer solution in 43 wells with an overall injection rate of 32, 000 bbls/d. Polymer concentration is 3, 000 ppm, and well head injection pressure ranges from 90 barg to 130 barg. Considering the significant polymer volumes, a development with powder form has been selected with f 12 tons/day of nominal consumption. While requiring a larger footprint and slightly more CAPEX, it helped significantly reduce OPEX and transportation costs. In addition, specific equipment and technologies have been selected and implemented to prepare a highly viscous polymer solution, reduce maturation time and prevent any form of chemical or mechanical degradation. This paper will also present recent developments with the use of non-shearing choke valves to avoid significant drop in polymer viscosity. This project is now in operation for 18 months (April 2022) with more than 2, 8 million m3 of polymer solution injection. High injection reliability has been achieved (>98%) for all logistics, operations, and topside equipments. The Chengdao 22F EOR polymer flood pilot project drains an oil-bearing area of 3.21 square kilometers with an estimated initial oil in place (STOIIP) of 80.7 million bbls (12.04 million tons) of which 28.8 million bbls (4.3 million tons) are located within the central producing area. A total of 22 injection and 57 production wells have been drilled. It is predicted that cumulative oil production will reach 28.2 million bbls (4.21 million tons) after 15 years, with an estimated incremental oil recovery factor of 11.6% from polymer injection. Following polymer injection, the water cut start to drop from 90.2% down to 85.0% at few production wells and should continue to drop down to 80%. This paper will provide guidelines to help implementing successfully large-scale chemical EOR projects in an offshore environment. It will also present recent developments in non-shearing choke valves and specific equipment to optimize the injection-facilities’ overall footprint.