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Offshore faulted block oilfields with considerable technical development risks are frequently encountered in offshore oilfield exploitation. This paper proposes a two-level fuzzy hierarchy technique for an integrated evaluation of the technical development risk of offshore faulted block oilfields. The proposed technique can classify the technical recoverable volume quality according to the characteristics of offshore faulted block oilfields. It includes a two-level evaluation index and a two-level fuzzy hierarchy evaluation method. We conducted a thorough evaluation of the proposed technique, using actual offshore faulted block oilfields in Australia and China. The results verified the reliability and applicability of the proposed technique. •. Developed a technique for the quality evaluation of offshore block faulted gas field. •. Established the two-level evaluation index system of the technique. •. Established the two-level fuzzy hierarchy evaluation method of the technique. •. Two different offshore block faulted gas fields were evaluated by using the technique. [ABSTRACT FROM AUTHOR]

Modelling of hydraulic fracturing often deals with elastic deformation of rocks and fractures. Some rocks, such as the rock-salt and shale, however, displayed viscoelastic behaviour in both field investigation and lab creep tests. This time-dependent deformation poses a challenge in modelling and characterising of fracture propagation in such formations, thus adding complexity in a multi-physics scenario. In this paper, we intend to numerically model fracture propagation in viscoelastic formation and investigate the effect of creep on crack propagation and crack geometry. To incorporate pore pressure effect, we couple fluid diffusion with shale matrix viscoelasticity in the hydraulic fracturing propagation model. Therefore, a procedure for numerical modelling hydraulically-driven fracture propagation in poro-viscoelastic formation is developed. The method uses a poro-viscoelasticity theory to describe the fluid diffusion and matrix creep in solid skeleton, in conjunction with cohesive law based damage criteria to simulate crack growth and fluid flow in the crack. The modelling took shale as the representative sample. The viscoelastic properties were obtained via creep tests of shale samples from Roseneath formation, Cooper Basin, Australia. Results show that the hydraulically induced fracture tends to be wider and longer in creep formation. What's more, the propagation pressure is also lower than that in poroelastic formation. Fluid diffusion from crack to the matrix is more efficient due to modulus decay. For mixed-mode fracturing, the creep of the formation facilitates the process of reorientation with higher fracture propagation speed between kink points. • A fully coupled poro-viscoelasticity fracture propagation model was adopted for hydraulic fracturing in creep formation. • Fractures propagating in creep formation tend to be wider and longer with low propagation pressure. • Fluid diffusion from crack to the matrix is more efficient due to modulus decay in creep formation. [ABSTRACT FROM AUTHOR]