EOR Pilot Tests With Modified Enzyme in China Qing-xian Feng, Xian-ping Ma, Li-hong Zhou, Ding-bo Shao, Xiao-lin Wang, and Bao-yan Qin, Dagang Oil Field Co. Abstract: Micro and macro evaluations were conducted to understand modified enzyme EOR mechanisms using various fluids. Huff n puff tests and flooding tests were carried out with variable modified enzymes concentrations in several reservoirs. Resulted production performances were considerably improved. At reservoir temperature 50-80°C, lab experiment indicated that the modified enzyme solution was adaptable to both light and heavy oil and was not sensitive to minerals water with bivalent cation (1000mg/l) and high salinity (10%). The enzyme working performances were further enhanced with microorganism occurrence in the solution. Micro modeling experiment revealed that spontaneous emulsification and solubilization could take place between the modified enzyme and crude with emulsion particle 2-6μm in diameter, which is produced through striping as a result of solubilization. Core desorption and flooding experiments presented that desorbed crude volume and displacement efficiency were related to modified enzyme concentrations which usually ranged 5 to 10% with the optimum being 8%. In optimal conditions, recovery can be averagely increased by 16.9%. Experiments also proved that the modified enzyme and crude oil could form emulsion but the emulsion was not stable. One specific pilot test with modified enzyme had achieved additional oil production 22,869 bbl. Introduction With time in oil development, some oil components precipitate and composites of organic and inorganic scales are deposited. Formation fine grains migrate and clays wells. These are barriers to fluid flow and productivity, causing much underground oil tobe unrecoverable. Modified enzymes were applied to improve biological activity of normal enzymes and to protect pay by opening pore paths and, thus, to introduce, stimulate, and merge Remaining oil into flows. Huff ’n’ puff and flooding tests that have been implemented in Dagang, Shengli, Daqing, and others both in China and elsewhere all show improved performance (Ying-li and Shu-lan 2000;Wang et al. 2002; Deng et al.2006; Wang et al. 2005; Kong et al. 2005; Harris and McKay 1998; Stanley et al. 1999; Al-Otaibi et al. 2005). It is not quite clear why and to what extent it works, so a collection of experiments were performed to evaluate the modified-enzyme EOR mechanism. A field test was made and is presented here. At the end of last century, Apollo Separation Technology Company began to successfully use enzyme for huff'n'puff operation in producers to overcome pore plugs from organic material deposition. This was introduced to China early this century. In March2004, such an agent was applied on Well Yong 8-52 in Shengli Oilfield, Shangdong, China. Improved production was sustained for 180 days with 10,961bbl of additional oil. Similar performance was observed in Baise oilfield, Guangxi, China, and in other fields. With development for 2 years in China, more than 100 wells saw enzyme application and success ratio greater than 88%. Enzyme-flooding tests in Daqing even recorded more than 1:3 in investment-to-output value. Revised: SPE Reservoir Evaluation & Engineering v. 12 - no.1 - p. 79-87 (February 2009)