Thermal recovery of offshore coalbed methane reservoirs: Flow characteristics of superheated steam in wellbores

Methane in coalbed methane (CBM) reservoirs is mainly in the adsorbed state, and has both free and dissolved states. The proportion of adsorbed methane can be as high as 90% or more. Field practice shows that low methane desorption efficiency is one of the keys affecting CBM development. The adsorption of methane is significantly affected by temperature, and the desorption efficiency increases with the increase of temperature. In this paper, the wellbore flow during the development of CBM reservoirs by injection of superheated steam is taken as the research object, and the superheated steam flow model is established considering the influence of seawater disturbance caused by the phase change of superheated steam. The study found: (a) In the formation section wellbore, the superheated steam has the highest temperature value. (b) The temperature of the super-heated steam is affected by both the Joule Thompson effect and the heat loss effect. (c) The longer the wellbore in the seawater section, the lower the temperature of the superheated steam in the wellbore. (d) Superheated steam is only suitable for shallow sea conditions.

Automated summary

Methane in coalbed methane (CBM) reservoirs is mainly adsorbed and can exist in both free and dissolved states. Low methane desorption efficiency is a key factor affecting CBM development. Temperature has a significant impact on methane adsorption, with desorption efficiency increasing with temperature. This study focuses on wellbore flow during CBM reservoir development using superheated steam injection and establishes a superheated steam flow model considering the influence of seawater disturbance caused by phase change. The study reveals that the temperature of superheated steam is highest in the formation section wellbore, affected by both the Joule Thompson effect and heat loss, and decreases as the wellbore extends through the seawater section. Superheated steam is only suitable for shallow sea conditions.