This paper reviews the role and importance of thermo-hydro-mechanical (T-H-M) processes in some applications that are of particular relevance to the petroleum industry: thermal loading of a borehole, influence of the rate of pressurization on the breakdown pressure, stability of a borehole, influence of leak-off on the fracturing pressure and closure pressure in hydraulic fracturing, poroelastic mechanisms for deviating hydraulic fracture, and dependence of the drilling response on the virgin pore pressure. Special emphasis is placed on the drained and undrained responses (the two limiting states that characterize T-H-M processes) and on the need to determine criteria defining the conditions for which the two limiting responses are effectively reached.
Cet article met en evidence Ie rôle et I'importance des processus thermo-hydro-mecaniques (T-H-M) dans certaines applications relevant du domaine de I'industrie petroliere: chargement thermique d'un trou de forage, influence du taux de pressurisation sur la pression de claquage, stabilite de puit, influence des pertes de fluide en fracturation hydraulique, mechanismes poroelastiques de deviation des fractures hydrauliques, influence de la pression de pore initiale sur l'energie mecanique depensee lors du forage. L'accent est mis sur les reponses drainees et non-drainees (deux etats limites caracterisant les processus T-H-M) et sur le besoin d'obtenir les critères definissant les conditions pour lesquelles ces reponses limites sont pratiquement atteintes.
In dieser Veröffentlichung wird die wichtige Rolle von Thermo - Hydro - Mechanischen (T-H-M) Prozessen, wie thermische Belastung von Bohrlöchern, Einfluβ der Drucksteigerungsrate auf den erreichbaren Druck, Einfluβ des leak-off Verhaltens auf die Schlieβkraft bei hydraulischer Riβaufweitung, poroelastischer Mechanismus zur Erklarung der Abweichung bei hydraulischer Riβaufweitung und Abhanigigkeit der Bohrreaktion vom unbeeinfluβten Porendruck, die vor allem fuer die Erdölindustrie von spezieller Relevanz sind, zusammengefaβt. Besondere Bedeutung wird auf die drainierten und undrainierten Reaktionen im Untergrund (die zwei limitierenden Zustande welche T-H-M Prozesse charakterisieren) und auf die Notwendigkeit, Kriterien zu bestimmen bei welchen diese beiden Grenzreaktionen erreicht werden, gelegt.
In the last decade, there has been a strong research emphasis on evaluating the overall implication of the presence of pore fluid on geomechanical processes, through an analysis of initial/ boundary value problems. This is also the main topic of this paper, which reviews the consequences of thermo-hydromechanical interaction on some petroleum engineering processes such as drilling, borehole stability, and hydraulic fracturing. There are three basic mechanisms that cause pore pressure to evolve with time:
diffusive mass transport of the pore fluid driven by non-equilibrated pore pressure perturbations,
"mechanical" change in pore volume, and
differential thermal expansion (or contraction) of the fluid and the pore space.
Of fundamental importance, is the intrinsic rate sensitivity (or time-dependency) introduced by the diffusion mechanism (both hydraulic and thermal). In contrast, the time-dependency associated with the "mechanical" pore pressure change is external, in the sense that it is imposed by the boundary conditions. A related issue is the existence of two limiting deformation states, i.e. drained and undrained. This is a key feature of the response of fluid-infiltrated materials. In undrained deformation, there is no variation of fluid content in a material element, and the pore pressure change with respect to some initial conditions is exclusively related to the variation of pore volume under isothermal conditions, and also to a mismatch of the thermal expansivity of the fluid and the solid under non-isothermal conditions. Depending on the constitutive model of the rock (and the loading history), the pore volume change can be either elastic or elastoplastic, In the former case, ∆p is proportional to change in the mean stress and a variation of temperature.
