Moving CBM Reservoirs into Production – Developing a New Workflow

Abstract

Abstract There have recently been extensive attempts to better model and simulate coal bed methane (CBM) reservoirs - something which is particularly pertinent to Australia which has an estimated 198 billion cubic meters (Bcm) of CBM resources and Queensland where AUS$50 billion worth of CBM projects are currently in progress. Yet, while most reservoir simulators are equipped to simulate fluid flow in CBM reservoirs, there is a need for a workflow that is better able to locate the sweet spots in CBM. To this end, this paper will examine recent technical developments in reservoir modelling and how modelling tools can be better utilised to optimise production in CBM reservoirs through simulation. The paper will look at the challenges in collecting the right amount of data to compile an accurate characterisation of a preexisting fracture network (cleats) and its structural complexities. The current low gas prices sometimes prevent the acquisition of such data – data that is an essential input to drilling strategies, fracture programme design and well spacing. The paper will also examine how the transport along a wellbore is not only controlled by the fractures around the well but also by the drained volume. In such cases, the pre-existing fractures and their reactivation during the fracturing stage are not always sufficient to determine the amount of gas that can be recovered during production. With this in mind, the paper will also look at the challenge of generating a good estimation of the size of the gas-in-place within CBM reservoirs and the role of reservoir modelling and simulation within this area.