Research on dynamical overflow characteristics of a vertical H₂S‐containing natural gas well

Abstract

This work aims to explore the overflow characteristics of a vertical H2S‐containing natural gas well. A two‐phase flow model for H2S‐containing natural gas well combining with a transient temperature prediction model was established to simulate the overflow process of a vertical H2S‐containing natural gas well. The model was validated by reproducing the field data of Well Longhui #2. The effects of H2S content, mud displacement, drilling fluid density, geothermal gradient, and reservoir permeability on the overflow characteristics of a vertical H2S‐containing natural gas well were studied and analyzed in this work. Results indicate that bubble, slug, and churn flows constitute the main flow patterns in the whole overflow process. The higher the H2S content is, the more obviously the gas void fraction increases. The phase change position of H2S is closer to the wellhead at lower H2S content. An increase in mud displacement indicates the decreases in overflow time. As drilling fluid density increases, the release position of H2S moves up, and the overflow time and shut‐in casing pressure increase. The initial gas void fraction is higher and the gas invasion volume will be larger in gas reservoirs with higher permeability. As the reservoir permeability increases, the shut‐in casing pressure rises while the overflow time declines. With higher geothermal gradient, the wellbore temperature tends to be higher at the same depth, leading to an increase in the H2S solubility. The gasification starting position is further away from the wellhead at higher geothermal gradient. The results of this work could provide important theoretical basis and technical guidance for drilling engineers to reduce a blowout risk during drilling of H2S‐containing natural gas well.

Influence of Instantaneous Shut‐In on the Safety of Tubing String in Ultra‐Deep High‐Temperature and High‐Pressure Gas Well

“…[1][2][3][4][5] With the continuous development of these HTHP oil and gas wells, the difficulty of oil and gas production continues to increase, which puts forward higher requirements for the integrity of the gas wellbore. [6][7][8][9][10] During the production process of HTHP gas wells, the fluid flow rate in the tubing string is very fast, which not only applies to the start-up and shut-in conditions, [11][12][13] but also accounts for the continuous changes in production of gas well overtime. Under these conditions, the fluid flow rate in the tubing string will change greatly and cause momentum conversion, resulting in severe pressure fluctuation in the tubing string.…”

Simultaneous detection of hydrogen sulfide and carbon dioxide based on off‐axis integrated cavity output spectroscopy using a near‐infrared distributed feedback diode laser

“…These gases are usually useless or even harmful, causing difficulties in the extraction, transportation, processing and use of natural gas 1,2 . When H 2 S, CO 2 and other gases associated with the exploitation of sulfur‐containing natural gas encounter water in the process of natural gas pipeline transportation, they will form an acidic environment and cause erosion to natural gas pipelines and related facilities, which not only affects the natural gas transportation and storage, but also may cause natural gas pipeline leakage and lead to a series of safety accidents 3,4 . Hence the development of a real‐time and reliable sensor system for simultaneous monitoring H 2 S and CO 2 concentration level is of great significance in the field of natural gas pipeline transportation and safe production.…”