Formation-Evaluation Log-Off Results for Coalbed-Methane-Field Development
Authors: Carpenter Chris 
Published: January 2017

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 176823, “Formation-Evaluation Log-Off Results Comparing New- Generation Mining-Style Logging Tools With Conventional Oil-and-Gas Logging Tools for Application in Coalbed-Methane-Field Development,” by T. Gan, B. Balmain, A. Sibgatullin, M. Ward, and F. Liu, Arrow Energy, and E. Murphy and L. Cook, Shell, prepared for the 2015 SPE Asia Pacific Unconventional Resources Conference and Exhibition, Brisbane, Australia, 9–11 November. The paper has not been peer reviewed.

An operator’s coalbed-methane (CBM) -development projects in Queensland, Australia, are designed with a large volume of wells that will need to be drilled and evaluated over the next decade. At present, the cost of logging is forcing the operator to choose between early data coverage vs. restricted logging. To resolve this issue, the operator has embarked on a series of technology trials to investigate various cost-effective formation-evaluation solutions. This paper presents the results of a comparison of state-of-the-art mining logging technology and conventional oil-and- gas logging technology.

Introduction

The Surat basin is a broad intracratonic downward that covers an area of approximately 300 000 km2 in southeastern Queensland and northeastern New South Wales. The operator’s interests are solely in Queensland. The basin comprises a primarily nonmarine Jurassic succession overlain by a mixed nonmarine and marine Early Cretaceous succession. (For detailed geological information, please see the complete paper.) The operator’s proposed Surat CBM project is located in the eastern part of the basin, in Queensland only, with an area of 22 000 km2.

It is important to use geophysical logs as part of the data-acquisition program, especially during the early development phase. The geophysical logs are used for coal identification, derivation of coal properties, and coal ranking. Current mining logging technology consists of a basic logging suite such as gamma ray, density/photoelectric factor, and neutron and resistivity tools. For advanced logging operations in exploration and appraisal wells, these must be replaced by conventional oil-and-gas logging tools to ensure holistic subsurface characterizations and front-end engineering work for future project- development decision making.

Logging-Technology-Trial Results for CBM Data Acquisition

Trials proved the availability of a cost-saving proposal for logging vertical development wells, which can meet formation-evaluation objectives while minimizing the costs of openhole logging. This is primarily achieved by running a basic logging suite of density, gamma, caliper, and deviation. An important distinction to consider is that, in conventional oil and gas, density sensitivity is usually down to approximately 2.0 g/c m3 because of the use of weighted muds. In CBM, formation water or very lightweight muds are used and coal densities can be as low as 1.2 g/cm3, pushing the boundaries of density-tool measurements to obtain such low readings.

Mining-Drillpipe-Push (MDP) Logging Tools. This logging-conveyance method involves the addition of a composite collar within the drilling bottomhole assembly before the production section is drilled. Once total depth (TD) is reached, the drillpipe is broken open at surface and the logging tools are pumped down and latched into the composite collar. The pipe is then tripped out of the well, and the logging occurs through the composite collar in memory mode. The logging tools for this trial included density, gamma, dual-neutron, and resistivity.