Reservoir Characterisation Using Distributed Temperature Sensing in CSG Development: Application in the Surat Basin, Queensland, Australia

Abstract

This paper discusses the use of distributed temperature sensing (DTS) in QGC's Surat Basin wells, and how this new technology has been used to improve reservoir characterisation through enhanced resolution of zonal productivity and flowing contributions.In stacked reservoirs with zones of varying quality, it is vitally important to allocate production volumes to flowing zones in order to adequately characterise the reservoir and create a representative dynamic simulation model that can accurately match reservoir productivity and depletion.For conventional oil and gas production, subsurface allocation of flowing contributions can be achieved through the use of production logging tools, which provide a measurement of volumetric flow rate and fluid density along the completed well length. The nature of Coal Seam Gas (CSG) well completions reduces the options available for allocation of flow to zones. Also, the producing characteristics of a CSG well can make this zonal allocation more complicated. Firstly, the lower zones of QGC's Surat wells are subject to higher back-pressure due to the column of water sat in the annulus, rising above the pump location. Secondly, the de-watering and subsequent de-sorption periods complicate matters, where initially 100% water flows from a zone followed by a gradually increasing gas-water-ratio: the rate of transition from water to gas production is expected to be different for each producing zone. Additionally, due to the stress dependency of coal fracture permeability during the de-watering phase, and later the impact of gas de-sorption on fracture permeability, different zones might be expected to show larger or smaller changes in productivity with time: to understand this would require repeatable measurements through the production life of wells.In this work, DTS technology has been proven, for the first time in QGC's Surat CSG wells, as a means of achieving subsurface allocation of well test kh. This is important for the justification of permanent installations that will allow ongoing zonal allocation of produced volumes. The impact of this methodology on history match quality and reservoir characterisation accuracy is discussed. It is suggested that these new workflows could prove very beneficial in the characterisation of CSG reservoirs.

Novel Well Test Design for the Evaluation of Complete Well Permeability and Productivity for CSG Wells in the Surat Basin

“…A trial to get zonal allocation during an AAFT using a Distributed Temperature Sensing (DTS) installation was performed (Furniss et al 2014). But the temporary installation removed the cost advantage of the AAFT and therefore DTS-based zonal allocation is only applicable for a selected number of long-term installations.…”