Study on Screening and Evaluation of Foam Drainage Agents for Gas Wells with High Temperature and High Pressure

Abstract

Foam drainage gas recovery technology is a chemical method to solve the serious bottom-hole liquid loading in the middle and late stages of gas well production, and the optimization of foam drainage agents (referred to as FDAs) is the key to the technology. According to the actual reservoir conditions, a high-temperature and high-pressure (HTHP) evaluation device for FDAs was set up in this study. The six key properties of FDAs, such as HTHP resistance, dynamic liquid carrying capacity, oil resistance, and salinity resistance, were evaluated systematically. Taking initial foaming volume, half-life, comprehensive index, and liquid carrying rate as evaluation indexes, the FDA with the best performance was selected and the concentration was optimized. In addition, the experimental results were verified by surface tension measurement and electron microscopy observation. The results showed that the sulfonate compound surfactant (UT-6) had good foamability, excellent foam stability, and better oil resistance at high temperature and high pressure. In addition, UT-6 had stronger liquid carrying capacity at a lower concentration, which could meet the production requirement when the salinity was 80 000 mg/L. Therefore, compared with the other five FDAs, UT-6 was more suitable for HTHP gas wells in block X of the Bohai Bay Basin, whose optimal concentration was 0.25 wt %. Interestingly, the UT-6 solution had the lowest surface tension at the same concentration, with the generated bubbles being closely arranged and uniform in size. Moreover, in the UT-6 foam system, the drainage speed at the plateau boundary was relatively slower with the smallest bubble. It is expected that UT-6 will become a promising candidate for foam drainage gas recovery technology in HTHP gas wells.

Mitigating Liquid Loading in Gas Wells Using Thermochemical Fluid Injection: An Experimental and Simulation Study

“…Gas wells suffering from liquid loading issues are incapable of removing the liquid associated with produced gas from the wellbore. 1 − 3 Natural gas wells can experience liquid loading, particularly as they age. 4 − 6 An annular or mist flow occurs in a vertical well when the gas velocity is high enough to carry the liquids to the surface without any buildup.…”

“…Gas wells suffering from liquid loading issues are incapable of removing the liquid associated with produced gas from the wellbore. − Natural gas wells can experience liquid loading, particularly as they age. − An annular or mist flow occurs in a vertical well when the gas velocity is high enough to carry the liquids to the surface without any buildup. , The inability of produced liquids to be removed from the wellbore by produced gas is known as liquid loading of a gas well . The well’s upward gas velocity must fall below a threshold level for this phenomenon to occur, at which time the liquid that was initially flowing upward starts to sink back. , This liquid builds up at the bottom of the well, where it reduces the production rate, destabilizes multiphase flow in the well (after changes in flow regime), increases hydrostatic back pressure on the reservoir, and, in extreme situations, kills the well…”

Assessment of forecasting hydrate blockage in foam drainage gas recovery wellbore

“…After the water at the well's bottom contacts the foaming agent, a large amount of low-density water containing foam is generated by stirring the natural gas flow, which is carried from the well's bottom to the wellhead with gas flow, to discharge accumulated liquid at well's bottom. 3,4 Natural gas hydrates, also known as "combustible ice," are cage-shaped compounds formed by natural gas and water. 5,6 Natural gas hydrates are characterized by a vast resource volume, with a global total reserve of 7.6 × 10 18 m 3 , which is twice the combined known reserves of carbon-containing compounds, including coal, petroleum, and conventional natural gas.…”

“…As shown in Figure 1, the foam drainage process refers to injecting a certain surfactant (foaming agent) that can foam in water from the wellhead to the well's bottom. After the water at the well's bottom contacts the foaming agent, a large amount of low‐density water containing foam is generated by stirring the natural gas flow, which is carried from the well's bottom to the wellhead with gas flow, to discharge accumulated liquid at well's bottom 3,4 …”

Study on Dynamic Liquid-Carrying Process of Foaming Agent and Establishment of Mathematical Model

“…There are many methods to study the properties of foaming agents, the traditional methods are mainly Ross–Miles method and the Bikerman method, In recent years, many new methods have been used to study foam properties, such as electrical conductivity, − near-infrared and optical properties, as well as high-energy particles, scanning electron microscopy and sound velocity methods, to achieve the expansion of foam properties at the microscopic level. For foaming agents, the existing detection methods mainly focus on static and short-term indicators under different conditions, including foaming capacity, foaming stability, liquid-carrying capacity of foaming agents, etc., ,, as well as the study of the foam instability mechanism extended from the study of foam stability. − However, in the process of gas well foam drainage and gas recovery, foaming agents are used as a liquid-carrying agent . Most attention is paid to the relationship between the dosage of the agent and the amount of liquid carried and the duration of action, the relationship between the dosing cycle and formation water production, and how long the fluid can be keep carrying out of the wellhead after dosage.…”