Coal-Seam-Gas-Field Management: Forecasting During Shutdown and Recovery

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 167088, ’Coal-Seam-Gas-Field Management: Well-Performance and Production Forecasting During Shutdown and Recovery Operations,’ by S. Magee, T. Ogilvie, and C. White, Origin Energy, prepared for the 2013 SPE Unconventional Resources Conference and Exhibition - Asia Pacific, Brisbane, Australia, 11-13.November. The paper has not been peer reviewed. Queensland, Australia, is currently host to a number of coal-seam-gas (CSG) to liquefied-natural-gas (LNG) projects under development. However, the need to build field deliverability before the availability of export gas markets presents a significant challenge. CSG wells must be dewatered; during this process, gas production may need to be constrained. The ability to manage and forecast production performance in a field-turndown scenario is therefore critical. A study of production data from CSG-production-interruption events was conducted to determine how wells reacted to turndown of gas-production rates. Introduction There are currently three major CSG-to-LNG projects under construction in Queensland. A number of other projects are also proposed and are currently in various stages of planning and approval. The transition from a domestic gas market to an export LNG market presents many opportunities and challenges for gas producers. When the LNG-export facilities are commissioned, the gas demand markedly increases over a short period of time. To ensure the best return on capital investment and to satisfy export contracts, the use of these export facilities needs to be maximized as soon as possible after commissioning. To optimize field output at the time that downstream facilities become operational, the CSG reservoirs must be de watered in advance, resulting in an increase of produced-gas volumes along with the early water production. One challenge for upstream producers is how to manage field deliverability during a period (the ramp period) when there is little ability for existing markets to absorb significant increases in gas supply. Possible solutions include gas storage, flaring, and the constraining of gas production while continuing to dewater the reservoir (turndown), or some combination of these and other strategies. The optimum strategy is likely to be a function not only of reservoir performance but also of the various commercial, operational, and project-execution constraints faced by each operator. Review of Historical Production Data Historically, field turndown in the areas of study has been achieved through the selective choking or shut-in of individual producing wells. The primary factors in well selection have been gas and water production, completion status, and liquid-lift calculations.