Exploration and Production companies operating in Coal Seam Gas (CSG) consistently face challenges in regards to efficient well monitoring and operations. CSG wells are completed with artificial lift and have fluid flow in both tubing and annulus. The water is being produced with the help of artificial lift through tubing and gas is produced through annulus. Well production depends on artificial lift performance and flow profile within the tubing and fluid level in annulus. The well modelling technique requires a common nodal solution from tubing and annulus which requires an iterative procedure to suggest optimum operating parameters and predicts rates for various scenarios.
CSG wells have low gas rates which induce slugging in the annulus and hence adversely affect the well performance. The unwanted down hole pressure variation leads to reduction in lift efficiency both in tubing and annulus. The operating condition of artificial lift requires optimisation to operate the well at maximum production potential. The fluctuation in liquid rates from wells needs to be minimised for process stabilisation and hence reduction in back pressure effects on other wells in surface network.
The main objective of the exercise presented in this paper is to model the flow path inside tubing and annulus for an artificially lifted CSG well. There is currently a gap in the industry on how such wells should be modelled since the water & gas are separated down hole and they follow different flow paths. A flowing well has a common down hole pressure at different surface flowing tubing head pressure and flowing casing pressure. This project involves development of a software tool on the basis of industry research which can execute performance analysis in CSG wells. In addition, the scope of the project includes identifying basic guidelines for operating a CSG well.
To achieve this objective all issues related with CSG well operation were collectively analysed and scope of work was drawn. The requirement of performance analysis tool for unconventional wells was acknowledged and the workflow for optimum well operation was proposed with available software applications. An Excel based application running on visual basic code was created which can communicate with a multiphase pressure calculator and perform system analysis for CSG wells. The proposed tool was developed and validated on real field data from BG Group.
This paper covers the operating issues, proposed workflow for performance analysis for CSG wells, development stages of the tool, its application on real field data, validation with field measurements and limitation associated with developed workflow. This thesis also covers the main aspects considered to monitor performance of CSG wells; the effect of surface and downhole parameters on well performance and how these concepts and diagnosis can help to achieve production targets in CSG field.