Abstract
Detailed information is provided for the design and construction of nitrogen drilling in a coal seam. Two prototype wells are considered. The Guo model is used to calculate the required minimum gas injection rate, while the Finnie, Sommerfeld, and Tulsa models are exploited to estimate the ensuing erosion occurring in pipe strings. The calculated minimum gas injection rates are 67.4 m3/min (with water) and 49.4 m3/min (without water), and the actual field of use is 90–120 m3/min. The difference between the calculated injection pressure and the field value is 6.5%–15.2% (formation with water) and 0.65%–7.32% (formation without water). The results show that the Guo model can more precisely represent the situation of the no water formation in the nitrogen drilling of a coal seam. The Finnie, Sommerfeld, and Tulsa models have different sensitivities to cutting densities, particle size, impact velocity and angle, and pipe string hardness.
Highlights
Two prototype wells in a coalbed methane exploration area are studied, which should be regarded as the first directional (Well D) and horizontal (Well H) wells in the world to implement nitrogen drilling technology in coal seams
The amount of gas injection is too small to meet the requirements of carrying rock and liquid, and excessive gas injection will lead to the erosion of the pipe string and the expansion of the wellbore
For Wells D and H that implement nitrogen drilling technology in coal seams in areas with abundant rainfall, this paper uses the Guo model to calculate the gas injection volume and gas injection pressure of the two wells, and uses the Finnie model, Sommerfeld model, and Tulsa model to analyze the erosion of string
Summary
Two prototype wells in a coalbed methane exploration area are studied, which should be regarded as the first directional (Well D) and horizontal (Well H) wells in the world to implement nitrogen drilling technology in coal seams. The actual temperature is used to replace the average temperature, and the inclination angle is introduced into the model to calculate the minimum gas injection rate in the straight, inclined, and horizontal sections [5–8]. International University proposed the erosion wear model [11], which includes target properties, particle shape, as well as the particle impact velocity and angle. The erosion wear model proposed by Tulsa University includes target properties, particle shape, particle impact velocity, and angle, among others [12]. For Wells D and H that implement nitrogen drilling technology in coal seams in areas with abundant rainfall, this paper uses the Guo model to calculate the gas injection volume and gas injection pressure of the two wells, and uses the Finnie model, Sommerfeld model, and Tulsa model to analyze the erosion of string
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