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The mechanical behavior of chalk under laboratory conditions simulating reservoir operations

Technical Report:

Abstract

This work has been carried out with the chalk mechanics research society at the University of Stavanger. The PhD thesis is thus a continuation to the long line of experimental chalk research carried out honoring the academic principles investigating fundamental mechanisms of chalk mechanical behavior. Simultaneously, the work and objectives have been a joint project with the Ekofisk license (the COREC program) and the Valhall license ensuring a strong link to important operating challenges associated with hydrocarbon production from chalk reservoirs. The overall goal has been to address fundamental chalk behavior in a controlled laboratory environment and simultaneously approach conditions as close as possible as those in-situ. The focus in this thesis may be subdivided into five main categories: ?? Experimental challenges regarding the effective stress relations. ?? Time and rate effects during depletion close to in-situ conditions. ?? Seawater impact on creep close to in-situ conditions. ?? Basic mechanisms for chemical water weakening. ?? Effect of acid injection as a function of various chalk properties. The contribution of the pore fluid pressure to the reduction of the effective stress during loading of fully saturated high porosity chalk (>40% porosity) has often been assumed to be represented by an effective  More>>
Authors:
Publication Date:
Jul 01, 2010
Product Type:
Technical Report
Report Number:
N-2010:104
Resource Relation:
Other Information: Doctoral theses at UIS; ISSN 1890-1387; Thesis or Dissertation; TH: Thesis (Ph.D); refs., figs., tabs
Subject:
02 PETROLEUM; RESERVOIR ENGINEERING; RESERVOIR PRESSURE; LIMESTONE; CARBONATE ROCKS; MECHANICAL STRUCTURES; SIMULATION; FLUID INJECTION
OSTI ID:
1011175
Research Organizations:
University of Stavanger. Stavanger (Norway)
Country of Origin:
Norway
Language:
English
Other Identifying Numbers:
Other: ISBN 978-82-7644-414-8; TRN: NO1105142
Availability:
Available at: http://brage.bibsys.no/uis/handle/URN:NBN:no-bibsys_brage_13330
Submitting Site:
NW
Size:
88 p. pages
Announcement Date:
Apr 18, 2011

Technical Report:

Citation Formats

Omdal, Edvard. The mechanical behavior of chalk under laboratory conditions simulating reservoir operations. Norway: N. p., 2010. Web.
Omdal, Edvard. The mechanical behavior of chalk under laboratory conditions simulating reservoir operations. Norway.
Omdal, Edvard. 2010. "The mechanical behavior of chalk under laboratory conditions simulating reservoir operations." Norway.
@misc{etde_1011175,
title = {The mechanical behavior of chalk under laboratory conditions simulating reservoir operations}
author = {Omdal, Edvard}
abstractNote = {This work has been carried out with the chalk mechanics research society at the University of Stavanger. The PhD thesis is thus a continuation to the long line of experimental chalk research carried out honoring the academic principles investigating fundamental mechanisms of chalk mechanical behavior. Simultaneously, the work and objectives have been a joint project with the Ekofisk license (the COREC program) and the Valhall license ensuring a strong link to important operating challenges associated with hydrocarbon production from chalk reservoirs. The overall goal has been to address fundamental chalk behavior in a controlled laboratory environment and simultaneously approach conditions as close as possible as those in-situ. The focus in this thesis may be subdivided into five main categories: ?? Experimental challenges regarding the effective stress relations. ?? Time and rate effects during depletion close to in-situ conditions. ?? Seawater impact on creep close to in-situ conditions. ?? Basic mechanisms for chemical water weakening. ?? Effect of acid injection as a function of various chalk properties. The contribution of the pore fluid pressure to the reduction of the effective stress during loading of fully saturated high porosity chalk (>40% porosity) has often been assumed to be represented by an effective stress coefficient close to unity. The significance of this work may be summarized in five main findings: ?? The experimentally determined effective stress coefficient, ?, differs significantly from the theoretical predicted, when compressibility is used as basis for the evaluation. ?? The experimental results show that high porosity chalk cores with similar porosity, depleted with considerably different load rates obtain similar amount of final deformation. This raise uncertainty about the importance of rate dependency of chalk under completely drained conditions. ?? A load rate dependency on the uniaxial strain stress path has been demonstrated. Further, the development of transient creep show similar dependency considering load rate. The PhD thesis relates both these findings to the evolution for failure at grain scale, as described by the nucleus of failure concept. ?? Seawater injection at elevated temperatures chemically weakens the chalk. The degree of weakening is primarily seen by the demonstrated volume effect; a core subjected to continuous injection of synthetic seawater weakens significantly more than cores subjected to limited volume injection. Evidence of newly precipitated minerals as a result of core flooding confirms ongoing dissolution-precipitation processes taking place. ?? The acid stimulation study suggests, through visual inspection of acidized cores, that porosity, permeability and material strength influence the created geometry. The acid seems to spread more easily in higher porosity and softer chalk. (AG)}
place = {Norway}
year = {2010}
month = {Jul}
}