SPE Journal
Volume 14, Number 1, March 2009, pp. 54-66

Summary

Typical gelled-polymer treatments to treat fractured rock consist of injecting in-line-mixed gelant into the reservoir for times usually much longer than the bulk gel time of the gelant. Flow experiments were conducted to determine the effect of shear on the flow properties of the gelant for durations greater than the bulk gel time. In-line-mixed gelant was injected through a 1,031-ft-long tube to simulate a fracture treatment. Flow resistance increased down the tubing to steady values indicating gelation of the flowing system. Similar flow experiments were conducted by injecting preformed gel through the tubing. Flow resistances decreased down the tubing to steady values, indicating breakdown of the gel structure. Steady flow resistances of the downstream sections were higher during the injection of in-line-mixed gelant compared to injection of preformed gel, and both were much lower than literature values determined where preformed gel was injected through short fractured rocks and short lengths of tubing.
Gel samples underwent syneresis after they were formed during shear flow in the tubing and in a rheometer. Interpretations of flow-resistance data from the injection of in-line-mixed gelants and preformed gels in long tubing are presented.

Introduction

Gelled-polymer treatments are applied to injection and production wells to modify the permeability and alter the flow in the reservoir to reduce water production and enhance oil production. Approximately 1,400 treatments have been applied in the Arbuckle formation in Kansas where high water cuts (>95%) are thought to be the result of flow from the underlying aquifer through high-conductivity vuggy conduits or fractures. A typical treatment (Portwood 2005) consists of bullheading 4,000 bbl of a polyacrylamide/chromium acetate gelant in production wells that were completed in the top few feet of the formation. Polymer concentration in the gelant is increased through the treatment, with an average of approximately 5,000 ppm. Chromium (Cr) solution is mixed in-line with the polymer solution just before injection at rates that give a polymer/Cr weight ratio of approximately 40. Bulk gel times at reservoir temperature of approximately 40°C range from 2 to 12 hours, depending on the loading. Gelant is injected for approximately 4 days at a typical injection rate of 1,080 B/D. The in-line-mixed gelant is subjected to shear flow in the injection tubing for approximately 30 minutes and enters the formation at a temperature of approximately 20°C as a fluid gelant, not a gel. The temperature of the gelant approaches the formation temperature, and the gelant forms a gel as it flows in the reservoir for time periods that are many times greater than the bulk gel time. This work was focused on the effect that shear flow has on the flow properties of the gelant and on the gel properties after flow.

© 2009. Society of Petroleum Engineers

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History

• Original manuscript received: 10 January 2007
• Meeting paper published: 28 February 2007
• Revised manuscript received: 21 November 2007
• Manuscript approved: 24 June 2008
• Published online: 16 March 2009
• Version of record: 1 March 2009