Interburden Isolation & Slotted Liner Placement as Solids Control Measure to Improve Well Performance by Reducing Operating Costs and Maximising Gas Production

Abstract

Solids production in coal seam gas wells have been a large contributor to down-hole completion failure in the Surat Basin, Australia. Since 2016, solids production has become an important focal point for well quality improvement for the Surat Basin operator and has focused its efforts on trying to a) understand the mechanism of pump failure related to solids, b) quantifying the origin of the solids, c) understanding where they come from geologically and d) developing best practices to optimise well designs and operating practices. This study has focused on improving drilling, completion and post-completion activities to reduce operating costs and maximise gas production. The implementation of formal procedural workflows and management of key performance indicators have formed the fundamentals for managing the delivery of quality wells through metrics such as interburden isolation, and thus reducing the risk of well impairment. Sourcing of additional equipment such as shorter slotted casing joints has increased the material limits for interburden isolation. The development of casing tally software has drastically reduced the risk of manual calculation errors and improved completions accuracy and efficiency. Solid samples have been taken from production water, completion tubing and well sumps. The samples from production water indicate that the average particle size is reduced with a reduction in fluid velocities. This inefficiency to remove the larger particles sizes coincides with a reduction in pump run-life due to settling of these solids in the tubing. An increase in periodic pump shut downs has also resulted in increased pump failure related to solids accumulation. Therefore, the optimisation of pump sizes and tubing designs plays a very important role in effective solids removal and increasing pump run-life. The average mineral composition of the solids samples may suggest that the majority of samples originate from the lower Juandah and upper Taroom formations. Further testing will be required to refine any hypothesis of solid origins and related strategies for more targeted isolation. A higher solids production correlates well with an increase in interburden exposure. The variable trends may indicate that some areas are more prone to solids production due to geological differences. Solids quantities do not demonstrate any noticeable trends over time for vertical wells but do increase over time for deviated wells. In some cases, solids quantities increase at ascending rates; this may suggest that the swellable packers are not creating effective seals and the well is washing away behind the packers and subsequently increasing the surface area of the wellbore. Through the reduction of exposed interburden, the potential risk of well impairment has been significantly reduced. Further work will be required to understand the effective use of swellable packers in deviated wells and possible strategies to overcome their shortcomings. Drilling bottom hole assembly design and changes to drilling parameters and practices have shown to improve borehole gauge to maximise the effectiveness of swellable packers. It is expected that, with a continual solids sampling program in place, a refined interpretation of solids production will be established over time, and an improved execution and operations strategy will be optimised to suit.