Rock Mechanics Of The Ekofisk Reservoir In The Evaluation Of Subsidence

Johnson, J.P.; Rhett, D.W.; Siemers, W.T.

doi:10.4043/5621-ms

Cited by 20 publications

(15 citation statements)

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“…7 shows PV reduction vs. applied isostatic stress and elapsed time for a sample from another prospect, Prospect B. (Similar transient creep has also been observed in chalks, 5 mary creep, there also exists steady-state creep and tertiary creep. See Ref.…”

Section: Pv Behaviormentioning

confidence: 56%

Deepwater Gulf of Mexico Turbidites— Compaction Effects on Porosity and Permeability

Ostermeier¹

1995

SPE Formation Evaluation

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The deepwater Gulf of Mexico is now a major area of activity for the U.S. oil industry. Compaction causes particular concern because most prospective deepwater reservoirs are highly geo-pressured and many have limited aquifer support; water injection may also be problematic. Thus, economic development may require significant drawdowns with ensuing compaction and its attendant problems.To address some of the issues associated with compaction, we initiated a special core-analysis program to study compaction effects on turbidite sand porosity and permeability specifically. This program also addressed a number of subsidiary but no less important issues, such as sample characterization and qual ity, sample preparation, and test procedures. These issues are particularly pertinent, because Gulf of Mexico turbidites are generall y unconsolidated, loose sands, and are thus susceptible to a whole array of potentially serious core-disturbing processes.One key result of the special core analysis program is that turbidite compressibilities exhibit large variations in both magnitude and stress dependence. These variations correlate with creep response in the laboratory measurements. The data suggest creep may be important because observed creep relaxation rates, although slow on a laboratory time scale, are much faster than typical reservoir drawdown rates.The effects of compaction on permeability are significant. To eliminate complicating effects caused by fines movement, we made oil flow measurements at initial water saturation. The measurements indicate compaction reduces permeability four to five times more than porosity on a relative basis.

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Section: Pv Behaviormentioning

confidence: 56%

Deepwater Gulf of Mexico Turbidites— Compaction Effects on Porosity and Permeability

Ostermeier¹

1995

SPE Formation Evaluation

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“…With the aid of a finite element analysis Gambolati et al (1999a) proved that under the effect of a pressure drawdown ∆p the reservoir deforms as if it were confined within a natural oedometer subject to an effective vertical stress increase equal to ∆p. This was already noticed 10 years earlier by Johnson et al (1989) who observed (p. 171) that "A large ratio of lateral extent to vertical thickness…means that the compaction will occur largely in the vertical direction with minimal horizontal displacements. Tests Downloaded by [Northeastern University] at 04:58 21 November 2014 to simulate compaction in the subsurface should be confined tests that prevent the rock from undergoing any lateral deformation".…”

Section: Mechanics Of Reservoir Compaction and Migration To The Grounmentioning

confidence: 61%

Reservoir compaction and land subsidence

Gambolati

Ferronato

Teatini

2006

Revue Européenne de Génie Civil

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Subsurface hydrocarbon removal induces a reservoir compaction that migrates to the ground surface and causes the land to subside. While compaction depends primarily on the fluid pore pressure drawdown, the thickness and the mechanical compressibility of the depleted formation, the amount of compaction reaching the surface depends on the depth and size of the producing field and the stiffness of the overburden. This paper presents a list of the most famed sites worldwide that have experienced anthropogenic land subsidence because of underground fluid withdrawal and reviews the basic mechanisms controlling the reservoir compaction and the related ground settlement. Finally, some mathematical models, that can be effectively used to simulate and predict the occurrence, and the most recent techniques for accurately and timely measuring and monitoring the deep compaction and the land surface displacements are described.RÉSUMÉ. L'exploitation d'hydrocarbures provoque une compaction souterraine qui se propage à la surface et cause des affaissements. Tandis que cette compaction dépend essentiellement de la diminution de pression intersticielle et de la compressibilité mécanique de l'encaissant, la magnitude de la subsidence résultante en surface dépend de la profondeur, des dimensions du réservoir, et de la rigidité des couches de sol sus-jacentes. Ce papier présente une liste de sites mondialement connus qui ont subi des subsidences anthropogéniques, à cause de la baisse de la nappe d'eau, et passe en revue les mécanismes essentiels qui contrôlent la compaction mentionnée et la subsidence superficielle relative. Finalement, quelques modèles mathématiques qui peuvent être effectivement utilisés pour simuler et prévoir le phénomène, aussi bien que les techniques les plus récentes pour mesurer précisément la compaction en profondeur et les déplacements de surface sont décrits.

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“…Generally, c M is considered to be the most representative parameter for the correct description of the in situ compaction of sedimentary rocks and hence for the most realistic prediction of the related land subsidence (Johnson et al, 1989;Ruddy et al, 1989). Recent numerical results by Gambolati et al (1999) provide further evidence that the loaded sediments in the reservoir deform following an oedometric path.…”

Section: Structural Modelmentioning

confidence: 99%

Waterdrive dynamics and enhanced land subsidence over productive gas fields: Application to Dosso degli Angeli reservoir, Ravenna, Italy

Baù¹,

Gambolati²,

Teatini³

2000

Theory, Modeling, and Field Investigation in Hydrogeology: A Special Volume in Honor of Shlomo P. Neumans 60th Birthday

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An active waterdrive (or confining aquifer) generally plays a favorable role in sustaining the pore-pressure in productive gas reservoirs. However, it may contribute significantly to spread the pressure decline and enlarge the land settlement bowl around the field. Moreover, it may continue to compact, and hence produce additional subsidence, for a long time after the field abandonment. The dynamics of waterdrive depletion, and related compaction, are primarily controlled by the aquifer extent and its rock hydromechanical properties for any given field pumping program. After production has been completed water progressively floods the reservoir with a moving water-gas interface until a stable equilibrium is ultimately achieved. The process of residual waterdrive depressurization and concurrent reservoir repressurization is a nonlinear one, where nonrecoverable sediment compaction exerts an important influence on the overall occurrence. A nonlinear finite element model to predict land subsidence over a depleted gas field and the associated waterdrive is developed and applied to the gas reservoir of Dosso degli Angeli, Ravenna, Italy. Numerical results show that the waterdrive compaction accounts for two-thirds of the maximum land subsidence of more than 30 cm recorded in 1992 at the well shutdown and suggest that a residual land settlement of almost 10 cm is to be expected by the year 2042 over the two areas of Porto Garibaldi and Casal Borsetti, located a few kilometers south and north of the field, respectively.

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Rock Mechanics Of The Ekofisk Reservoir In The Evaluation Of Subsidence

Cited by 20 publications

References 0 publications

Deepwater Gulf of Mexico Turbidites— Compaction Effects on Porosity and Permeability

Deepwater Gulf of Mexico Turbidites— Compaction Effects on Porosity and Permeability

Reservoir compaction and land subsidence

Waterdrive dynamics and enhanced land subsidence over productive gas fields: Application to Dosso degli Angeli reservoir, Ravenna, Italy

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