Richard A. Schultz

A review of deformation bands in reservoir sandstones: geometries, mechanisms and distribution

Abstract Deformation bands are common subseismic structures in porous sandstones that vary with respect to deformation mechanisms, geometries and distribution. The amount of cataclasis involved largely determines how they impact fluid flow, and cataclasis is generally promoted by coarse grain size, good sorting, high porosity and overburden (usually >500–1000 m). Most bands involve a combination of shear and compaction, and a distinction can be made between those where shear displacement greatly exceeds compaction (compactional shear bands or CSB), where the two are of similar magnitude (shear-enhanced compaction bands or SECB), and pure compaction bands (PCB). The latter two only occur in the contractional regime, are characterized by high (70–100°) dihedral angles (SECB) or perpendicularity (PCB) to σ1 (the maximum principal stress) and are restricted to layers with very high porosity. Contraction generally tends to produce populations of well-distributed deformation bands, whereas in the extensional regime the majority of bands are clustered around faults. Deformation bands also favour highly porous parts of a reservoir, which may result in a homogenization of the overall reservoir permeability and enhance sweep during hydrocarbon production. A number of intrinsic and external variables must therefore be considered when assessing the influence of deformation bands on reservoir performance.

Causes and mitigation strategies of surface hydrocarbon leaks at heavy-oil fields: examples from Alberta and California

Identification and mitigation of leaks of subsurface fluids such as hydrocarbons at many heavy-oil fields is a first-order concern to operating companies, their regulators and the public. A variety of leaks have been documented at heavy-oil fields in Alberta (Canada) and California (USA). Although the petroleum geology and tectonic framework of fields in these areas differ significantly, production-related uplift of overburden and dilation of pre-existing fractures due to cyclic steam injection are likely to have facilitated the leakage events. As a result, integration of overburden characterization and monitoring with management of steam pressures may provide an effective means of risk mitigation of major leakage events.