8 research outputs found
Microfracturing and microporosity in shales
Shales are ubiquitous rocks in sedimentary basins, where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories (waste waters, CO2, nuclear fuels). Moreover, when they contain organic matter, they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial, a process referred to as primary migration. And when the hydrocarbons cannot escape, these rocks can be exploited as oil or shale gas reservoirs. While the presence of fractures at the outcrop scale has been described, the existence of fractures at smaller scales, their link with microporosity, the mechanisms that created them, their persistence over geological times, and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data.
Here, we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability. One question is whether such microfractures, when observed in outcrops or in drilled core samples extracted from boreholes, are related to decompaction and do not exist at depth. Another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation. The mechanisms of microfracture development are described. Some have an internal origin (fracturing by maturation of organic matter, dehydration of clays) while others are caused by external factors (tectonic loading). Importantly, the amount of microfracturing in shales is shown to depend strongly on the content in 1) organic matter, and 2) strong minerals. The nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale. Their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso- to macro-scales. Such percolating microfracture networks could control both the long-term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks. Finally, possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed
Molecular alterations induced by a high-fat high-fiber diet in porcine adipose tissues: variations according to the anatomical fat location
Modelling the mechanical impact of CO2 injection into a carbonate reservoir of the Paris Basin
CO2 injection into a depleted hydrocarbon field or a deep saline aquifer can induce a variety of more or less strongly coupled physical and chemical processes. In an oil field pore pressure variations due to hydrocarbon production and CO2 injection directly impact mechanical properties, through stress field changes in and around the reservoir. Such modifications can lead to reservoir or caprock failures, reservoir compaction or uplift and the reactivation of faults. These phenomena can influence the sealing efficiency of geological storage. To be able to correctly design CO2 storage, and to perform the associated risk assessment, an accurate prediction of reservoir and subsurface mechanical behaviour is needed. To assess geological hazards related to hydrocarbon extraction or to underground gas storage, we use integrated 3D geomechanical modelling. In this approach a reservoir simulator is used first to compute the whole pressure history during depletion and CO2 injection periods. The pressure computed by the multiphase fluid-flow description of the reservoir simulator is then used as an input parameter of a geomechanical simulator. This is a one-way coupling procedure, that does not account for feedback of mechanical deformation on pore pressure. The results of the geomechanical modelling are analysed in order to study the induced deformation and in-situ stress changes due successively to oil production and CO2 injection. The influence of both production and injection steps are illustrated by a numerical model built from a carbonate reservoir in the context of the Paris Basin. The modelling is performed in the framework of the project PICOREF, supported by the French National Agency of Research
Applying underground gas storage experience to geological carbon dioxide storage: A case study from Australiaâs Otway Basin
3D geomechanical modelling for CO2 geologic storage in the Dogger carbonates of the Paris Basin
CO2 injection into a depleted hydrocarbon field or aquifer may give rise to a variety of coupled physical and chemical processes. During CO2 injection, the increase in pore pressure can induce reservoir expansion. As a result the in situ stress field may change in and around the reservoir. The geomechanical behaviour induced by oil production followed by CO2 injections into an oil field reservoir in the Paris Basin has been numerically modelled. This paper deals with an evaluation of the induced deformations and in situ stress changes, and their potential effects on faults, using a 3D geomechanical model. The geomechanical analysis of the reservoirâcaprock system was carried out as a feasibility study using pressure information in a âone wayâ coupling, where pressures issued from reservoir simulations were integrated as input for a geomechanical model. The results show that under specific assumptions the mechanical effects of CO2 injection do not affect the mechanical stability of the reservoirâcaprock system. The ground vertical movement at the surface ranges from â2 mm during oil production to +2.5 mm during CO2 injection. Furthermore, the changes in in situ stresses predicted under specific assumptions by geomechanical modelling are not significant enough to jeopardize the mechanical stability of the reservoir and caprock. The stress changes issued from the 3D geomechanical modelling are also combined with a MohrâCoulomb analysis to determine the fault slip tendency. By integrating the stress changes issued from the geomechanical modelling into the fault stability analysis, the critical pore pressure for fault reactivation is higher than calculated for the fault stability analysis considering constant horizontal stresses.Sandrine Vidal-Gilbert, Jean-Francois Nauroy and Etienne Bross
Le développement durable à découvert
Vingt ans aprĂšs la premiĂšre confĂ©rence de Rio, quâest devenue la proposition de conduire nos sociĂ©tĂ©s vers un dĂ©veloppement durable ? AdoptĂ© par les uns, utilisĂ© comme faire-valoir par les autres, ce concept de dĂ©veloppement durable est souvent vidĂ© de son sens. Or, lâimpact exponentiel des activitĂ©s humaines sur les ressources naturelles, la santĂ© des populations et le milieu exige dâexpliquer ce quâil est prĂ©cisĂ©ment. Quâest-ce que le dĂ©veloppement durable aujourdâhui ? Quâen est-il de la disponibilitĂ© des ressources et de lâusage que nous en faisons ? Dans le domaine de lâeau, du climat, des sols, de la biodiversitĂ© ? En milieu rural, sur le littoral ou encore en milieu urbain, lĂ oĂč la majoritĂ© de la population va vivre dâici 2050, comment consommons-nous au fil du temps, Ă travers les territoires ? Quelles incidences les activitĂ©s humaines ont-elles sur les ressources, sur la santĂ© des populations et sur le milieu lui-mĂȘme ? Les relations entre lâhumanitĂ© et lâenvironnement doivent-elles Ă©voluer ? Autant de questions posĂ©es Ă des scientifiques qui Ă©claircissent la complexitĂ© des interactions entre les systĂšmes et proposent des solutions pour un avenir sur le long terme. De nos Ă©cosystĂšmes Ă nos modes de consommation, des risques naturels aux nouvelles technologies ou aux pollutions, des usines du futur au traitement des dĂ©chets, Le dĂ©veloppement durable Ă dĂ©couvert informe, explique, partage tout ce que la science actuelle est capable dâapporter au dĂ©fi majeur du xxie siĂšcle : comment mieux comprendre la complexitĂ© des enjeux qui nous concernent tous et assurer le dĂ©veloppement de lâhumanitĂ© sans dĂ©truire son biotope. Ăconomistes, physiciens, sociologues, agronomes, Ă©cologues... plus de 150 chercheurs se sont mobilisĂ©s pour associer leur expertise Ă leur regard critique et dĂ©crire, comprendre, modĂ©liser, imaginer, illustrations et schĂ©mas Ă lâappui, les outils destinĂ©s Ă construire les sociĂ©tĂ©s Ă©quitables de demain
High Risk of Anal and Rectal Cancer in Patients With Anal and/or Perianal Crohnâs Disease
International audienceBackground & AimsLittle is known about the magnitude of the risk of anal and rectal cancer in patients with anal and/or perineal Crohnâs disease. We aimed to assess the risk of anal and rectal cancer in patients with Crohnâs perianal disease followed up in the Cancers Et Surrisque AssociĂ© aux Maladies Inflammatoires Intestinales En France (CESAME) cohort.MethodsWe collected data from 19,486 patients with inflammatory bowel disease (IBD) enrolled in the observational CESAME study in France, from May 2004 through June 2005; 14.9% of participants had past or current anal and/or perianal Crohnâs disease. Subjects were followed up for a median time of 35 months (interquartile range, 29â40 mo). To identify risk factors for anal cancer in the total CESAME population, we performed a case-control study in which participants were matched for age and sex.ResultsAmong the total IBD population, 8 patients developed anal cancer and 14 patients developed rectal cancer. In the subgroup of 2911 patients with past or current anal and/or perianal Crohnâs lesions at cohort entry, 2 developed anal squamous-cell carcinoma, 3 developed perianal fistulaârelated adenocarcinoma, and 6 developed rectal cancer. The corresponding incidence rates were 0.26 per 1000 patient-years for anal squamous-cell carcinoma, 0.38 per 1000 patient-years for perianal fistulaârelated adenocarcinoma, and 0.77 per 1000 patient-years for rectal cancer. Among the 16,575 patients with ulcerative colitis or Crohnâs disease without anal or perianal lesions, the incidence rate of anal cancer was 0.08 per 1000 patient-years and of rectal cancer was 0.21 per 1000 patient-years. Among factors tested by univariate conditional regression (IBD subtype, disease duration, exposure to immune-suppressive therapy, presence of past or current anal and/or perianal lesions), the presence of past or current anal and/or perianal lesions at cohort entry was the only factor significantly associated with development of anal cancer (odds ratio, 11.2; 95% CI, 1.18-551.51; P = .03).ConclusionsIn an analysis of data from the CESAME cohort in France, patients with anal and/or perianal Crohnâs disease have a high risk of anal cancer, including perianal fistulaârelated cancer, and a high risk of rectal cancer