The effects of calcium carbonate precipitation on high-velocity flow behavior in 3D printed fracture models

Abstract

A large amount of water is produced in oil and geothermal fields. Produced water is used in water injection for oil displacement and pressure maintenance in oil fields. However, there is a possibility of forming different precipitations when the injected water and formation water combine, which can cause serious problems in the reservoirs. In the world, more than 60% of oil and more than 40% of gas reservoirs are fractured carbonate rocks, and the mineral precipitation observed in these formations is mostly CaCO3 due to temperature and incompatibility between the injected and formation water. There are few techniques available for CaCO3 scaling removal due to their relative hardness and low solubility. In most cases, the scaled-up wells are caused by the formation of carbonate. In the well tests, it is seen that the flow from the matrix to the fracture is quite low, and the flow in the fracture dominates the whole flow. Therefore, it is essential to properly understand the kinetics of CaCO3 scale formation and its detrimental effect on fracture.It is known from studies that kinetic models can give better results in determining precipitation behavior. However, there are not enough experimental studies on the effects of flow on mineral precipitation in fractured media. Therefore, the kinetic and thermodynamic models are used in this study to reliably predict the amount of mineral precipitation. This work investigates the behavior of precipitation in different temperature conditions, laminar or turbulent flow conditions, and fracture properties like high roughness, length, and aperture. The amounts of precipitation in fracture under different conditions that have not been determined in the literature are given. After flow experiments, the amount of CaCO3 precipitation and pressure differences were measured. When the temperature is 80 °C, the flow rate is 4.16 × 10−5 m³/s, and the roughness is high, precipitation is 47.5% higher than when the temperature is 50 °C. Repeating the same fracture characteristics for different flow conditions in fracture flow tests is essential. By using 3D fracture models, the same fracture properties were obtained under different flow conditions.In addition to precipitation amounts, this article presents decreasing crack permeability due to precipitation. Precipitation of minerals can drastically influence the reservoir's permeability and ability to transmit mass and energy. With the pressure differences measured in the experiments, permeability decreases due to precipitation were calculated using Poiseuille's law (cubic law) for laminar flow and Forchheimer's equation for turbulent flow. After 3.5 days of flow, the study's permeability at high roughness and high flow decreased by 23% at 50 °C and 44% at 80 °C. This study's findings can help better understand that the permeability reduction of fracture is greater in turbulent flow conditions compared to laminar flow. In addition, temperature and high roughness are very effective parameters in precipitation and permeability change. At high temperatures and high roughness, more minerals precipitate, and permeability values decrease considerably. In the later injection periods, the decrease in permeability caused by the precipitation can make the fracture impermeable and increase the pressure losses during the injection.