That is, for small strains, the elements of the stress and strain tensors are related through where Furthermore, the strain response occurs instantaneously as soon as the stress is applied, and it is reversible—that is, after removal of a load, the material will be in the same state as it was before the load was applied. A plot of stress vs. However, in real rocks, the moduli increase as a function of effective stress, particularly at low stress.

Permeability determination Applying petrophysical techniques The pages linked above will acquaint the reader with the various aspects of the quantitative petrophysical determination of lithology, net pay, porosity, fluid contacts, water saturation, and permeability.

To make these calculations as accurately as possible, core and log data need to be integrated.

The routine-core-analysis data adjusted to reservoir conditions should be used to calibrate the logs for more-accurate calculations at the various wells. In applying petrophysical techniques it is valuable to remember: Lithology is determined by geologists working with cores and rock cuttings.

This information can be combined with log characteristics to identify depositional environments and characterize how these change vertically and areally throughout the reservoir.

The clay minerals present in the shales and the sandstone intervals, both as detrital and authigenic components, must be identified and quantified so that their effects on the logs and routine-core-analysis data can be adequately understood. Radioactive components present in the reservoir rocks must be identified and quantified so that the clay-mineral volumes derived from the GR log are not overstated.

Net pay calculations determine how much of the reservoir interval contributes to the technical calculations of in-place hydrocarbon volumes and fluid flow. If some portion of the reservoir interval is to be excluded as nonpay, the choice of cutoff should be based on flow considerations with a systematic and consistent approach.

Whatever nonpay cutoff is used, that cutoff will be somewhat arbitrary. Porosity can be computed from a variety of well logs density, sonic, or neutron in combination with routine-core data adjusted to reservoir conditions.

In sandstones in which the mineralogy and the hole conditions permit, foot-by-foot porosity calculations from the density log, calibrated to core, are likely to be the most accurate.

Correct fluid values are an integral part of the log evaluation. Porosity needs to be calculated accurately because, as well as its primary use, these values are also required for Sw and permeability estimates used directly in the volumetrics and flow calculations.

Minerals that affect the porosity calculations, such as clay and heavy minerals, need to be identified as part of the lithology determination. Water saturation can be computed by a number of independent methods using routine-core-analysis oil-based mud OBM -core Dean-Stark Sw data, special-core-analysis SCAL capillary pressure data, resistivity logs used in combination with SCAL rock electrical-property measurements, or some combination of these three datasets.

Integrated use of these various technical approaches will result in the most accurate Sw solution overall. In the water-saturation calculation using resistivity logs, the connate-brine salinity and its resistivity, Rw, can vary within the hydrocarbon column, but the extent of this variation is often not measured.

Also, the rock electrical properties may be a function of Sw. In most conventional Sw calculations using well logs, these are both assumed to be constant, and those assumptions can lead to significant errors in the calculated Sw values.

In the Sw calculation using Pc measurements, the laboratory tests are measurements of fluid volumes associated with cleaned and restored core plugs.

For application, the reservoir values of the interfacial-tension IFTcontact angle, and the wetting state of the reservoir generally must be estimated, along with several other factors.

Pc laboratory tests do not always achieve the equilibrium water saturation, or the same water distribution within the pore network as is present in the real reservoir.

Permeability values need to be adjusted to reservoir conditions. This adjustment is nonlinear, with poor-quality rocks having larger adjustments compared with those applied to high-quality rocks. Also, the calculated permeabilities at the wells should be compared with those obtained from pressure-buildup PBU analysis of flow tests.

The statistical correlation and calibration of core and log data requires that these data are properly depth aligned, have outliers deleted, and, if required, are mathematically transformed.

A variety of line-fitting techniques are available, but the "y-on-x" approach generally results in the most accurate predictor, except in highly variable, heterogeneous rocks. In any reservoir with a thick hydrocarbon column and large areal extent, more accurate-petrophysical calculations are made if the reservoir is vertically zoned or layered.

Different parameters for different areas of the reservoir may also be required for the most accurate solution. The Log Analyst May—June Essentials of Modern Openhole Log Interpretation. Baker Atlas, originally published by Western Atlas.

Log Data Acquisition and Quality Control, second edition. Core Laboratories UK Ltd.

Section 3: Hydraulic Grade Line Analysis |
An accurate determination of effective porosity is derived using a proprietary multi-mineral based system which integrates a multi-source clay volume logic and a series of algorithms which yield a pores size distribution. The pore size distribution is based on Nuclear Magnetic Resonance NMR data as well as an extensive core analysis database which gives an understanding of the texture of the reservoir rock. |

Petrophysical Analysis |
Maturation Migration In general, all these elements must be assessed via a limited 'window' into the subsurface world, provided by one or possibly more exploration wells. These wells present only a 1-dimensional segment through the Earth and the skill of inferring 3-dimensional characteristics from them is one of the most fundamental in petroleum geology. |

Rock physics reservoir characterisation software | Ikon Science |
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Information |
The fraction of the pore space occupied by water. The quantity of fluid usually hydrocarbon that can flow through a rock as a function of time and pressure, related to how interconnected the pores are. |

Geared for finding pay zones |
Various light minerals impact the density, neutron, and sonic logs, like: Coal Various radioactive minerals impact the GR log, such as: |

Noteworthy papers in OnePetro Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read External links Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro See also.Petroleum geology is the study of origin, occurrence, movement, accumulation, and exploration of hydrocarbon fuels.

It refers to the specific set of geological disciplines that are applied to the search for hydrocarbons (oil exploration. The addition of the RokDoc Reservoir Characterisation modules to your tool kit, brings a range of sophisticated tools; convert existing inversion volumes into meaningful and accurate geological rock properties for prospect evaluation.

One starting point is to determine rock types (petrofacies) wherein we identify: evaluation program choices and can be used as a reference during subsequent discussions on determination of various reservoir properties Log analysis is used universally and is generally successful in the identification of oil and gas reservoirs and .

Petrophysicists are employed to help reservoir engineers and geoscientists understand the rock properties of the reservoir, A key aspect of petrophysics is measuring and evaluating these rock properties by acquiring well log measurements Converted-wave analysis is also used to determine subsurface lithology and porosity.

Determining Reservoir Properties and Flood Performance From Tracer Test Analysis Authors G. Michael Shook Using the distribution of residence times extends the power of moment analysis by allowing for the determination of reservoir properties and flood performance as a function of time.

detailed reservoir simulation, production log. Understanding rock properties and how they react under various types of stress is important to development of a geomechanical model before drilling.

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A log analysis to determine reservoir rock properties