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The determination of a reservoir's mechanical properties is critical to reducing drilling risk and maximizing well and reservoir productivity. Acoustic logging can provide information helpful to determining the mechanical properties of reservoir rock. Mechanical properties include: * Elastic properties (Young's modulus, shear modulus, bulk modulus, and Poisson's ratio) [SeeStress strain relationships in rocks for calculations of these properties] * Inelastic properties (fracture gradient and formation strength) Elasticity is the property of matter that causes it to resist deformation in volume or shape. Hooke's law describes the behavior of elastic materials and states that for small deformations, the resulting strain is proportional to the applied stress. Depending on the mode of the acting geological force and type of geological media the force is acting upon, three types ofdeformation can result as well as three elastic moduli that correspond to each type of deformation.

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Materials (1.00)
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Oilfield Places: North America > United States > Kansas > Panoma Field (0.94)

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Well Drilling > Wellbore Design > Rock properties (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)

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Building geomechanical models

PetrowikiJanuary, 2018

This section outlines methods for determination of the stress magnitudes and the pore pressure. Overburden pressure, or Sv, is almost always equal to the weight of overlying fluids and rock. Thus, it can be calculated by integrating the density of the materials overlying the depth of interest (seeFigure 1). Figure 1--(a) Density logs for a subsea well beneath 1,000 ft of water, extrapolated to the mud line using an exponential curve. Density within the water column is 1.04 gm/cm[1]. Here, G is the gravitational coefficient.

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North America > United States > California > San Joaquin Basin > San Joaquin Valley > Belridge Field > Diatomite Formation (0.99)

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Well Drilling > Wellbore Design (1.00)
Well Completion (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
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PEH:Rock Properties

PetrowikiApril, 2017

Rock and fluid properties provide the common denominator around which we build the models, interpretations, and predictions of petroleum engineering, as well as geology and geophysics. We consider here the properties of sedimentary rocks, particularly those that make up hydrocarbon reservoirs. Usually, these consist of sandstones, limestones, and dolomites. We must be more inclusive, and consider rocks such as shales, evaporates, and diatomites because these provide the seals, bounding materials, or source rocks to our reservoirs. It is important to note that shales and claystones make up the most abundant rock type in the typical sedimentary column.

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Geophysics > Seismic Surveying > Seismic Processing (1.00)
Geophysics > Seismic Surveying > Seismic Interpretation > Seismic Reservoir Characterization (1.00)
Geophysics > Seismic Surveying > Borehole Seismic Surveying (0.92)
Geophysics > Seismic Surveying > Seismic Modeling > Velocity Modeling (0.68)

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Well Drilling > Wellbore Design > Rock properties (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
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Predicting wellbore stability

PetrowikiJanuary, 2016

Once a geomechanical model has been developed that quantifies the principal stress magnitudes and orientations, thepore pressure, and the rock properties, it is possible to predict the amount of wellbore instability as a function of mud weight and properties. This makes it possible to reduce drilling costs by keeping lost time low and by designing wells just carefully enough to minimize problems without excessive cost. A further benefit of considering geomechanical risk is that when problems are encountered, their causes can be recognized and plans can be in place to mitigate their effects with minimal disruption of the drilling schedule. Figure 1 shows the time-depth plot of an offshore well that was designed and drilled without the use of geomechanical modeling. After setting the first string to isolate a shallow hazard, the remaining casing depth points were selected based on drilling experience in an offset block, supplemented by pore pressures predicted using seismic data.

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Well Drilling > Wellbore Design > Wellbore integrity (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

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Elastic wellbore stress concentration

PetrowikiJanuary, 2016

Stress concentration around the wellbore can create breakouts, fractures, or failures. Understanding the stresses on rocks around wellbores is important to well design. For a vertical well drilled in a homogeneous and isotropic elastic rock in which one principal stress (the overburden stress,Sv) is parallel to the wellbore axis, the effective hoop stress,σθθ, at the wall of a cylindrical wellbore is given byEq. Here, θ is measured from the azimuth of the maximum horizontal stress, SHmax SH min is the minimum horizontal stress; Pp is the pore pressure; ΔP is the difference between the wellbore pressure (mud weight) and the pore pressure, and σΔT is the thermal stress induced by cooling of the wellbore by ΔT. At the point of minimum compression around the wellbore (i.e., atθ 0, parallel to SHmax), Eq. 1 reduces to The equations for σθθ; and σzz are illustrated in Figure 1 for a strike-slip/normal faulting stress regime (SHmax Sv SHmin) at a depth of 5 km, where the pore pressure is hydrostatic and both ΔP and σΔT are assumed to be zero for simplicity.

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Well Drilling > Wellbore Design > Wellbore integrity (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)

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Determining stress orientation

PetrowikiJanuary, 2016

The most reliable way to determine stress orientation is to identify features (either geological features or wellbore failures) the orientation of which is controlled by the orientations of the present-day in-situ stresses. Other methods that rely on observing the effect of stress on rock properties using oriented core have been found to be less reliable and subject to influence by factors other than in-situ stress. As previously discussed, wellbore breakouts occur in vertical wells at the azimuth ofSHmin, and drilling-induced tensile failures occur 90 to breakouts at the azimuth ofSHmax. Therefore, the orientations of these stress-induced wellbore failures uniquely define the orientations of the far-field horizontal stresses when using data from vertical wells. This is true for breakouts whether they are detected using 4-arm- or 6-arm-oriented caliper logs or using electrical or acoustic images, whether obtained by wireline orlogging while drilling (LWD) tools.

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North America > United States > Texas > Travis Peak Formation (0.99)
North America > United States > Mississippi > Travis Peak Formation (0.99)
North America > United States > Louisiana > Travis Peak Formation (0.99)
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Well Drilling > Wellbore Design > Wellbore integrity (1.00)
Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (1.00)
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Stress impact on rock properties

PetrowikiJanuary, 2016

Understanding rock properties and how they react under various types of stress is important to development of a geomechanical model before drilling. Some major geomechanical rock properties are described below. Penetrometer testing * 3.3 Estimating strength parameters from other data * 4 Nomenclature * 4.1 Subscripts * 5 References * 6 Noteworthy papers in OnePetro * 7 External links * 8 See also * 9 Page champions * 10 Category To first order, most rocks obey the laws of linear elasticity. In other words, the stress required to cause a given strain, or normalized length change (Δlk /ll), is linearly related to the magnitude of the deformation and proportional to the stiffnesses (or moduli), Mijkl. 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.

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Asia > Middle East > Saudi Arabia > Eastern Province > Al-Ahsa Governorate > Arabian Basin > Widyan Basin > Ghawar Field > Khuff D Formation (0.99)
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Predicting rock properties

PetrowikiJune, 2015

Many theoretical models have been developed to predict or correlate specific physical properties of porous rock. Most theoretical models are built on simplified physical concepts: what are the properties of an ideal porous media. However, in comparison with real rocks, these models are always oversimplified (they must be, to be solvable). Most of these models are capable of "forward modeling" or predicting rock properties with one or more arbitrary parameters. However, as is typical in earth science, models cannot be inverted from measurements to predict uniquely real rock and pore-fluid properties.

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