Abstract

Carbon dioxide is commonly injected during secondary or tertiary recovery to enhanced oil recovery. While CO2 can also cause some precipitation damage. Usually scale ions (Ca2+, Mg2+) in water react with CO2 to form solid precipitation that can plug the pores. In this report, CO2 is injected into the high salinity formation water, which makes the problem of inorganic precipitation by reaction with scale ions. A number of static experiments have been conducted about various reservoir pressures and temperatures when the pH and scale ions content changes in a high temperature high pressure Reactor. Thus, the aim of this report is to determine how the presence of inorganic precipitation during CO2 injections and the factors affecting the amount of CO2 with high salinity water generating inorganic precipitation. Results from XPS and SEM images of precipitation are also provided. The results indicate that there are three stages in the reaction between carbon dioxide and high salinity formation water, and the third stage with high temperature or low pressure produced precipitation is the most important. PH less than 7 can still produce precipitation. The larger the PH and the scale of the ion content, the more precipitation; at first with low temperature or high pressure, and then with the high temperature or low pressure produced the largest amount of precipitation.

1. Introduction

CO2 flooding technology is an important technology developed in the 1980s, which has been widely paid attention to by all countries in the world [1]. However, compared with oil, gas and other geologic fluids, CO2 is an active gas, and when it was injected into the ground, it is very easy to react with the formation of fouling ions in stratum water to produce precipitation and eventually change the physical and chemical properties of the reservoir [2]. Especially, the change of reservoir permeability will seriously affect the underground storage capacity of CO2 [3], so it is necessary to study and discuss the CO2 and formation water interaction.

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