scholarly journals Integration of geophysical and geomechanical data to understand the depletion of the Marlim field, Campos Basin

2021 ◽  
Vol 21 (1) ◽  
pp. 45-55
Author(s):  
Larissa Furtado Torres ◽  
Emílio Velloso Barroso
Keyword(s):  
Pore Pressure ◽  
3D Models ◽  
Pressure Gradients ◽  
Campos Basin ◽  
Sea Level Variations ◽  
Pore Pressure Gradient ◽  
4D Seismic ◽  
Seismic Anomalies ◽  
Potential Fluid ◽  
Field Area

Located in the Campos Basin, Brazil, the Marlim field, consists of two turbidite systems deposited during eustatic sea-level variations in the Oligocene/Miocene. The reservoir was discovered in 1985, and its production started to decline in 2002. One of the techniques selected to assist in the recovery of oil from the reservoir was the 4D seismic. However, its interpretation can be complex. In order to help address this issue, the present study proposed an analysis of the depletion of a small field area from 1997 to 2010, combining geophysical (4D seismic) and geomechanical (pore pressure) data through the construction of pore pressure 3D models for both years, which can be subtracted and compared to seismic anomalies. The results obtained were: an average depletion of 0.42 ppg (50.33 kg/m3) of pore pressure gradient in the field; the identification of potential fluid-flow barriers, such as an NW-SE-oriented channel and sealing faults; and the detection of two areas with an expressive presence of 4D seismic anomalies, one of them showing a quite evident difference between pore pressure gradients, suggesting field depletion. The use of very old and noisy seismic data hindered the application of this methodology. Nevertheless, this research demonstrated the relevance of estimating pore pressure in the reservoir and how this geomechanical parameter can be useful in assessing the level of field depletion.

Possible Reason of the Dependence of an Apparent Permeability on the Pressure Gradient at low Flow Rates in Laboratory Study

2021 ◽  
Author(s):  
Nikolay Baryshnikov ◽  
Evgeniy Zenchenko ◽  
Sergey Turuntaev
Keyword(s):  
Pressure Gradient ◽  
Pore Pressure ◽  
Pore Space ◽  
Low Flow ◽  
Pressure Gradients ◽  
Apparent Permeability ◽  
Flow Rates ◽  
Rock Samples ◽  
Pore Pressure Gradient ◽  
Filtration Properties

<p>Currently, a number of studies showing that the injection of fluid into the formation can cause induced seismicity. Usually, it is associated with a change in the stress-strain state of the reservoir during the pore pressure front propagation. Modeling this process requires knowledge of the features of the filtration properties of reservoir rocks. Many researchers note the fact that the measured permeability of rock samples decreases at low pressure gradients. Among other things, this may be due to the formation of boundary adhesion layers with altered properties at the interfaces between the liquid and solid phases. The characteristic thickness of such layer can be fractions of a micron, and the effect becomes significant when filtering the fluid in rocks with a comparable characteristic pore size. The purpose of this work was to study the filtration properties of rock samples with low permeability at low flow rates. Laboratory modeling of such processes is associated with significant technical difficulties, primarily with the accuracy limit of measuring instruments when approaching zero speed values. The technique used by us to conduct the experiment and data processing allows us to study the dependence of the apparent permeability on the pore pressure gradient in the range of 0.01 MPa/m, which is comparable to the characteristic pressure gradients during the development of oil fields. In the course of the study, we carried out laboratory experiments on limestone core samples, during which the dependencies of their apparent permeability on the pore pressure gradient were obtained. We observed a significant decrease in their permeability at low flow rates. In the course of analyzing the experimental results, we proposed that a decrease in apparent permeability may occur due to the effect of even a small amount of residual gas in the pore space of the samples. This has been confirmed by additional experiments. The possibility of clogging of core sample pore space must be considered when conducting when conducting laboratory studies of the core apparent permeability.</p>

Geopressure prediction from automatically‐derived seismic velocities

Geophysics ◽  
2001 ◽  
Vol 66 (6) ◽  
pp. 1937-1946 ◽  
Author(s):  
T. K. Kan ◽  
Herbert W. Swan
Keyword(s):  
Pressure Gradient ◽  
Pore Pressure ◽  
Cross Sections ◽  
Seismic Data ◽  
Seismic Velocities ◽  
Pressure Gradients ◽  
Sediment Deformation ◽  
Seismic Sections ◽  
Interval Velocities ◽  
Pore Pressure Gradient

The phenomenon of geopressure is essentially stratigraphic in nature. In most cases, its occurrence correlates strikingly well with some mappable geologic characteristics, such as lithology changes, sediment deformation, and faulting. High‐precision velocity estimates can be made from the apparent amplitude variations with offset (AVO) that result from moveout errors, even if the seismic data itself lacks any intrinsic AVO. These velocity estimates provide us with an opportunity to estimate cross‐sections and 3‐D volumes of the gradient of pore pressure with depth from surface seismic data. These cross‐sections and volumes may be obtained through the estimation of seismic interval velocities as a function of depth, subtraction of the shale compaction trend, and the calibration of trend deviations in terms of pore‐pressure gradients. When viewed in combination with stacked seismic sections, the pore‐pressure gradient sections provide the interpreter added information about the hydrogeology of the sediment. In this paper, we show examples of pressure gradients caused by a lithology change, sealing faults, and fluid migration flows. Pressure gradient cross‐sections are also extremely useful for the design of mud densities and casing prior to spudding a well.

scholarly journals Unsteady Seepage Behavior of an Earthfill Dam During Drought-Flood Cycles

Geosciences ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 17 ◽  
Author(s):  
Ziyang Li ◽  
Wei Ye ◽  
Miroslav Marence ◽  
Jeremy Bricker
Keyword(s):  
Pressure Gradient ◽  
Water Level ◽  
Pore Pressure ◽  
Internal Erosion ◽  
Reservoir Water ◽  
Reservoir Water Level ◽  
Upstream Slope ◽  
Earthfill Dams ◽  
The Stability ◽  
Pore Pressure Gradient

Climate change with extreme hydrological conditions, such as drought and flood, bring new challenges to seepage behavior and the stability of earthfill dams. Taking a drought-stricken earthfill dam of China as an example, the influence of drought-flood cycles on dam seepage behavior is analyzed. This paper includes a clay sample laboratory experiment and an unsteady finite element method seepage simulation of the mentioned dam. Results show that severe drought causes cracks on the surface of the clay soil sample. Long-term drought causes deeper cracks and induces a sharp increase of suction pressure, indicating that the cracks would become channels for rain infiltration into the dam during subsequent rainfall, increasing the potential for internal erosion and decreasing dam stability. Measures to prevent infiltration on the dam slope surface are investigated, for the prevention of deep crack formation during long lasting droughts. Unsteady seepage indicators including instantaneous phreatic lines, equipotential lines and pore pressure gradient in the dam, are calculated and analyzed under two assumed conditions with different reservoir water level fluctuations. Results show that when the water level changes rapidly, the phreatic line is curved and constantly changing. As water level rises, equipotential lines shift upstream, and the pore pressure gradient in the dam’s main body is larger than that of steady seepage. Furthermore, the faster the water level rises, the larger the pore pressure gradient is. This may cause internal erosion. Furthermore, the case of a cracked upstream slope is modelled via an equivalent permeability coefficient, which shows that the pore pressure gradient in the zone beneath the cracks increases by 5.9% at the maximum water level; this could exacerbate internal erosion. In addition, results are in agreement with prior literature that rapid drawdown of the reservoir water level is detrimental to the stability of the upstream slope based on embankment slope stability as calculated by the Simplified Bishop Method. It is concluded that fluctuations of reservoir water level should be strictly controlled during drought-flood cycles; both the drawdown rate and the fill rate must be regulated to avoid the internal erosion of earthfill dams.

scholarly journals Mathematical model of methane driven by hydraulic fracturing in gassy coal seams

2020 ◽  
Vol 38 (3-4) ◽  
pp. 127-147
Author(s):  
Weiyong Lu ◽  
Bingxiang Huang
Keyword(s):  
Mathematical Model ◽  
Hydraulic Fracturing ◽  
Pore Pressure ◽  
Hydraulic Fracture ◽  
Water Saturation ◽  
Reduction Rate ◽  
Space Time ◽  
Matrix Block ◽  
The Matrix ◽  
Pore Pressure Gradient

During hydraulic fracturing in gassy coal, methane is driven by hydraulic fracturing. However, its mathematical model has not been established yet. Based on the theory of ‘dual-porosity and dual-permeability’ fluid seepage, a mathematical model is established, with the cleat structure, main hydraulic fracture and methane driven by hydraulic fracturing considered simultaneously. With the help of the COMSOL Multiphysics software, the numerical solution of the mathematical model is obtained. In addition, the space–time rules of water and methane saturation, pore pressure and its gradient are obtained. It is concluded that (1) along the direction of the methane driven by hydraulic fracturing, the pore pressure at the cleat demonstrates a trend of first decreasing and later increasing. The pore pressure gradient exhibits certain regional characteristics along the direction of the methane driven by hydraulic fracturing. (2) Along the direction of the methane driven by hydraulic fracturing, the water saturation exhibits a decreasing trend; however, near the cleat or hydraulic fracture, the water saturation first increases and later decreases. The water saturation in the central region of the coal matrix block is smaller than that of its surrounding region, while the saturation of water in the entire matrix block is greater than that in the cleat or hydraulic fracture surrounding the matrix block. The water saturation at the same space point increases gradually with the time progression. The space–time distribution rules of methane saturation are contrary to those of the water saturation. (3) The free methane driven by hydraulic fracturing includes the original free methane and the free methane desorbed from the adsorption methane. The reduction rate of the adsorption methane is larger than that of free methane.

Crack problems in a poroelastic medium: an asymptotic approach

1994 ◽  
Vol 346 (1680) ◽  
pp. 387-428 ◽  
Keyword(s):  
Stress Intensity ◽  
Pressure Gradient ◽  
Pore Pressure ◽  
Asymptotic Method ◽  
Reciprocal Theorem ◽  
Fracture Plane ◽  
Intensity Factors ◽  
Wide Range ◽  
Crack Problems ◽  
Pore Pressure Gradient

We consider problems involving semi-infinite cracks in a porous elastic material. The cracks are loaded with a time dependent internal stress, or pore pressure. Either mixed or unmixed pore pressure boundary conditions on the fracture plane are considered. An asymptotic procedure that partly uncouples the elastic and fluid responses is used, allowing an asymptotic expression for the stress intensity factors as time progresses to be obtained. The method allows the physical processes involved at the crack tip and their interactions to be studied. This is an advance on previous methods where results were obtained in Laplace transform space and inverted numerically to obtain real-time solutions. The crack problems are formulated using distributions of dislocations (and pore pressure gradient discontinuities when necessary) to generate integral equations of the Wiener—Hopf type. The resulting functional equations are, of course, identical to those considered by C. Atkinson and R. V. Craster, but with the alternative formulation we develop an asymptotic procedure which should be applicable to other problems (e.g. finite length cracks). This asymptotic procedure can be used to derive asymptotic expansions for more complicated loadings when the numerical effort involved in evaluating results would be excessive. A large-time asymptotic method is also briefly described which complements the small-time method. The operators for poroelastic crack problems are inverted for a particular loading; the reciprocal theorem for poroelasticity is used together with eigensolutions of the fundamental problems to deduce the stress (or where necessary the pore pressure gradient) intensity factors for any loading. These formulae extend previous results allowing a wide range of different loadings to be considered. As an example, the stress intensity factor for a point loaded crack is derived and the asymptotic method is applied to this problem to derive a simple asymptotic formula. Finally, an invariant integral, which is a generalization of the Eshelby energy-momentum tensor, is used to derive integral identities which serve as a check on the intensity factors in some situations.

scholarly journals Experimental investigation of the functional mechanism of methane displacement by water in the coal

2020 ◽  
Vol 38 (9-10) ◽  
pp. 357-376
Author(s):  
Bingxiang Huang ◽  
Weiyong Lu ◽  
Shuliang Chen ◽  
Xinglong Zhao
Keyword(s):  
Pressure Gradient ◽  
Pore Pressure ◽  
Competitive Adsorption ◽  
Water Pressure ◽  
Water Injection ◽  
Experimental System ◽  
True Triaxial ◽  
Methane Source ◽  
Coal Rock ◽  
Pore Pressure Gradient

During hydraulic fracturing in a high-methane coal seam, there is a water-displacing-methane effect. A pseudo triaxle experimental system, which is opposite to the name of true triaxial system, for the water-displacing-methane effect was created. First, cylindrical coal samples in a methane adsorption equilibrium state, spontaneously desorbed. And then water was injected into the coal samples. The following was shown: (1) The displacement methane volume gradually rises with an increase of injected water, while the displacement methane rate tends to rise at first before declining later. Simultaneously, the water-displacing-methane process is characterised by a time effect. The methane displacement lags behind water injection. (2) Competitive adsorption and displacement desorption between the water and methane will promote adsorption methane into free methane, while the pore pressure increase caused by water injection will turn free methane into adsorption methane. The net free methane of the combination action provides a methane source for the water-displacing-methane effect. (3) A pore pressure gradient, which provides a power source for the water-displacing-methane effect, is formed and reduces gradually at the front of the water seepage along the seepage direction. The increase in water pressure can rapidly improve the pore pressure gradient and boost the displacement methane volume as well as improve displacement methane efficiency. (4) A starting porosity pressure gradient and limit pore pressure exist in the process of water-displacing-methane. When the pore pressure gradient is less than the starting pore pressure gradient, there is free methane in the coal rock, but it cannot be displaced. When the pore pressure is between the starting pore pressure and the limit pore pressure, the free methane can be displaced. When the pore pressure is greater than the limit pore pressure, the methane is almost completely adsorption methane, and water cannot be used to displace the free methane.

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