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Types of logs
Over time, many different types of logs have been developed to collect data about wellbores and subsurface formations. This article provides an overview of how various log types correspond to reservoir characteristics. It also provides links to articles discussing the various types of logs and selected applications in depth.
Relating log types and reservoir characteristics
Fig. 1 summarizes a number of specialized logging methods and how they relate to reservoir characteristics and the techniques for measuring them.
Fig.1 – This chart is separated into three concentric areas: the middle annular area indicates the subsurface properties to be evaluated, the innermost area indicates the specialized logging tools discussed here, and the outermost area indicates the logging tools discussed in other subchapters of this Handbook. The corresponding innermost and outermost areas show how the different tools complement each other in the investigation of particular subsurface properties.
Types of logs
- Resistivity and spontaneous (SP) logging
- Acoustic logging
- Nuclear logging
- Nuclear magnetic resonance (NMR) logging
- Mud logging
- Sonic logging
- Specialty logs
- Production logging
Applications and special conditions
- Logging while drilling (LWD)
- Directional survey
- Formation resistivity determination
- Porosity determination
- Permeability determination
- Fluid identification and characterization
- Layer thickness evaluation
- Lithology and rock type determination
- Saturation evaluation
- Fractional flow evaluation
- Fracture identification with acoustic logging
- Overpressure prediction using acoustic logging
- Geological applications of acoustic logging
- Rock mechanical properties
- Anisotropy analysis
- NMR applications
- Cuttings analysis during mud logging
- Formation evaluation during mud logging
- Production logging throughout well life
- Log interpretation
There are two principal drivers for the further advancement of logging technologies.
The first is the need for improved reservoir characterization to help us deal with problematic reservoirs that have low-permeability characteristics, thin beds, laminations, low-resistivity-contrast pay, and fracture networks. Fracture networks lead us to the question of carbonates and their petrophysical differences from clastic rocks. One might ask why it is that with so much technology available, the industry still perceives a shortfall in its interpretative capability. The reason is that recent attention has been directed at data acquisition and management rather than methods of interpreting the data themselves. Thus, for example, we have not yet succeeded in reconciling petrophysical data measured at different scales. The gap between our ability to measure and our ability to interpret the measurements widened still further during the 1990s, the decade of the horizontal well. This drove the analysis of downhole measurements further into three dimensions and emphasized the need for us to get more out of our data if our reservoir models are to deliver the greatest benefit.
The second technology driver is the cost-effectiveness of multiwell platforms from which deviated, extended-reach, horizontal, and multilateral wells can be drilled to target hydrocarbon accumulations that have been identified in a reservoir model. This heralds a further thrust in the need to drill more difficult subsurface environments in a way that allows full control of the wellbore trajectory. This, in turn, will require a full casing- and cement-evaluation service, especially with regard to the monitoring of casing deformation. Only in this way can one be assured of an absence of flow constrictions or impediments to tool deployment.
Both reservoir characterization and the cost-effectiveness of multiwell platforms will continue to benefit from further developments in data recording, transmittal, processing, and visualization, which have underpinned the technical progress made to date.
Noteworthy papers in OnePetro
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