The development of unconventional resources has seen a boom over past few years. Unconventional reservoir management & development is driving several new geoscience techniques, and novel ways of employing existing ones. Besides the organic geochemical evaluation, the approach from formation evaluation using electrical logs has started to play paramount role in the development of unconventional hydrocarbon exploration and exploitation. Conventional electrical log such as Gamma Ray, Density, Neutron has been utilized to aid geoscientist in quantifying properties such as kergogen volume and TOC, using various method such as Passey and Schmoker methods. Besides conventional electric log, advanced log such as Image log can also be utilized to optimize interpretation in unconventional resources.
Electrical image logs have an established place in structural analysis, sedimentology, and petrophysical propertie's calibration purpose for conventional reservoirs. The application of image log in structural analysis, including fracture analysis, can aid geoscientist in understanding their unconventional reservoirs better.
Image log is an oriented map of a property (resistivity, density or even radius) in the borehole wall. Image log is the inexpensive option, compared to coring, to acquire the map of borehole property. Acquired by both wireline and LWD, image log can reveal many borehole features and is very versatile in its application, from structure study, sedimentology study to petrophysic.
Now, image logs are turning out to be an increasingly attractive data source for planning effective hydraulic fracturing jobs and maximising the reservoirs producibility - a critical issue in shale gas development. Some of the main features to analyze for shale gas reservoirs are open fractures, drilling induced fractures, and breakouts-and all of these properties can be observed through image log.
Open fractures have a significant impact on system permeability and open fractures identified through wireline image logs help to estimate qualitative producibility. Permeability is a key factor in stimulation design.
Matrix permeability can be acquired and accurately measured with core analysis, or estimated with log evaluation. While system permeability can be more complex since it's not only taking the matrix permeability into account but also the contribution of open fractures.