No abstract

The classic Mandel solution associated with the well-known Mandel–Cryer effect is re-examined. Using Biot theory of poroelasticity, the solution of the Mandel problem is extended to include material transverse isotropy, as well as the compressibility of the pore fluid and the solid constituents of the soil–rock skeleton. Le résultat classique de Mandel, associé à l'effet bien comnnu de Mandel—Cryer, est réexamineé. En utilisant la théorie poro-é1astique de Blot, la solution du probléme de Mandel est étendue afin d'introduire l'anisotropie transverse du matériau, ainsi que la compressibilité des fluides présents dans les pores et celle des constituants solides du squelette du sol ou de la roche.

This paper presents an array of deformation-dependent flow models of various porosities and permeabilities relevant to the characterization of naturally fractured reservoirs. A unified multiporosity multipermeability formulation is proposed as a generalization of the porosity-or permeability-oriented models of specific degree. Some new relationships are identified in the parametric investigation for both single-porosity and dual-porosity models. A formula is derived to express Skempton's constant B by Biot's coefficient H and relative compressibility •b*. It is found that the recovery of the original expression for Skempton's constant B is largely dependent on the choice of 0', representing relative compressibility. The dual-porosity/dual-permeability model is evaluated through an alternative finite element approximation. The deformation-dependent fracture flow mechanism is introduced where the rock matrix possesses low permeability and fracture flow is dominant. A preliminary study of the reservoir simulation identifies the strong coupling between the fluid flow and solid deformation. curve where the important fluid interchange between fractures and matrix blocks occurs. In general, interporosity flow has been described by two mechanisms. The first is the simple quasi-steady state model proposed by Warren and Root [1963], followed by the more sophisticated unsteady state models of various versions [Kazemi, 1969; deSwaan-O., 1976; Duguid and Lee, 1977; Kucuk and Sawyer, 1980; Najurieta, 1980; Chen et al., 1985]. Some noticeable differences in terms of pressure distributions in the transition period result from the two different mechanisms. The transient flow and deformation behavior in a porous medium may result from changes in either the fluid pressure or total stress boundary conditions applied to the system. It is the admissibility of changes in total stress within the system (which may result from natural tectonic changes or human activities) that describes the essence of coupled deformation-dependent flow behavior within porous media and sets it apart from decoupled diffusive (flow) systems. Comprehensive coupling between stresses and pore pressures was first rationalized by Biot [1941] and later adopted in many applications to specific deformation flow systems [Ghaboussi and Wilson, 1973; Zienkiewicz et aI., 1977; Simon et al., 1984; Lewis and Schrefier, 1987; Detournay and Cheng, 1988]. In naturally fractured reservoirs where the medium consists of discrete fractions of varying solid compressibilities and permeabilities, a multiporosity/ multipermeability approach appears more appropriate.It is important to correctly characterize the behavior of naturally fractured reservoirs. For example, the exceptionally high oil rate recovered in the initial stages of reservoir production may lead to overestimating well production by assuming a higher storage to exist than exists in reality. It was assumed that the high matrix block storage would 1621

The identification of fracture barrier is important for optimizing horizontal well drilling, hydraulic fracturing, and protecting fresh aquifer from contamination. The word "brittleness" has been a prevalent descriptor in unconventional shale reservoir characterization, but there is no universal agreement regarding its definition. Here a new definition of mineralogical brittleness is proposed and verified with two independent methods of defining brittleness. Formation with higher brittleness is considered as good fracturing candidate. However, this viewpoint is not reasonable because brittleness does not indicate rock strength. For instance, fracture barrier between upper and lower Barnett can be dolomitic limestone with higher brittleness. A new fracability index is introduced to overcome the shortcoming of brittleness by integrating both brittleness and energy dissipation during hydraulic fracturing. This fracability index considers that a good formation for hydraulic fracturing is not only of high brittleness, but also requires less energy to create a new fracture surface. Therefore, the formation with lower fracability index is considered as a fracture barrier, while with higher fracability is considered as better fracturing candidate.Logging data from one well of Barnett shale is applied (1) to verify the principle of new brittleness and fracability index model; (2) and to demonstrate the process of screening hydraulic fracturing candidates employing fracability index model.