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Abstract
The first carbon dioxide (CO2) huff ‘n’ puff experimental project was conducted in 1997 in Jiangsu oilfield, China. This paper reviews design and performance data on 70 CO2 huff ‘n’ puff projects conducted in different wells in Jiangsu oilfield from 1997 to 2004. For the Jiangsu reservoirs with light crude oils, reversal of production damage and enhancement of oil swelling aided by gravity drainage are believed to be the most significant mechanisms contributing to increases in oil recovery. The objective of this paper is to examine important parameters, best practices and lessons learned that contributed to the success of CO2 huff ‘n’ puff operations and their use in further improvement in CO2 huff ‘n’ puff projects.

Introduction
Although most of today’s CO2 EOR projects involve large-scale continuous injection of CO2 solvent, there is increasing interest in cyclic CO2 injection into single wells. Typically, rapid injection of CO2 (or CO2/hydrocarbon blends) is followed by a shut-in period. The well is then returned to production and the response monitored. In reservoirs with poor interwell communication, this single-well approach may afford the only means of recovering tertiary oil by a CO2 process. In reservoirs where interwell communication has not been established, CO2 huff ‘n’ puff offers a fast, inexpensive alternative to traditional EOR methods.

Since 1984, the applicability of cyclic CO2 injection to the enhanced recovery of light oil has been examined with encouraging results. Reported coreflood data1,2 demonstrate that multiple cycles of CO2 injection can recover waterflood residual oil and that operating at miscible displacement conditions is disadvantageous. Many additional papers have since appeared in the literature3-8. All of these studies laid a solid theoretical foundation for the CO2 huff ‘n’ puff operation in field scale practices. However, field scale practice of cyclic CO2 injection is a technically sophisticated process. For this reason, a thorough knowledge of the reservoir and some important parameters of the cyclic CO2 process are essential to the success of the project.  The first huff ‘n’ puff experimental project was conducted in 1997 in Jiangsu oilfield. We review design and performance data on 70 CO2 huff ‘n’ puff projects conducted in different wells in the Jiangsu oilfield from 1997 to 2004. To improve design and continue to achieve a high-performance CO2 huff ‘n’ puff project, this paper presents lessons learnt and best practices on the 70 testes. The effects of reservoir parameters and design variables are discussed.