Sedimentary facies play an important role in controlling reservoir distribution, connectivity, and quality. Insufficient understanding of the relation between the sedimentary facies and reservoir quality frequently fails to meet the expectation of the oil recovery in the field development stage. The target C field in Bohai Bay basin is developed in a fan delta setting and the formation comprises stacked, multi-layered conglomerates and sandstones with rapid vertical variation. Continuous identification and characterization of sedimentary facies, including the lithology, grain-size, and petrophysical property, fluid components, and the sedimentary sequences is critical for mapping the reservoir quality and optimizing development wells’ location. Limited high resolution resistivity image log and core data are available for only three development wells, whereas most other development wells have LWD NMR data, conventional log and LWD density image. To extract more geological information from density image, the multi scale calibration among the resistivity image, density image and core data are executed. Thus, the sedimentary facies can be analyzed in those wells that only acquired density image. Moreover, the NMR bin porosity, T2 spectrum morphology and NMR fluid components (clay bound fluid, irreducible and movable fluid) were firstly involved in the sedimentary facies analysis together with LWD density image, conventional log, and mud log. The sedimentary structures from density image, the position and amplitude of NMR T2 spectrum, and the variation of bin porosity, and fluid components assist in identifying different sedimentary facies. In total, seven sedimentary facies are sequentially classified in the fan delta front setting: massive distributary channel, amalgamated distributary channel and mouth bar, pure sheet sand, shaly sheet sand and tributary bay and pro fan delta. These facies were linked in the petrophysical properties (effective porosity and permeability determined from NMR logs) to demonstrate the reservoir quality statistically. Then, six fluid typing templates using NMR, conventional logs, and LWD density image were firstly established which including clay bound water in pure shale zone, clay-bound and capillary bound water in silt/shale zone, light oil in low resistivity laminated sandstone, moveable light oil in pure sandstone oil zone, heavy oil in pure sandstone and water capillary bound/movable in water zone. The result shows the mouth bar and massive distributary channel sedimentary facies hold the highest effective porosities and amalgamated distributary channel and mouth bar hold the highest permeability. Lesser reservoir quality is observed for the pure sheet sand, followed by the shaly sheet sand. The poorest reservoir quality is associated with tributary bay with silty shale or shale. The innovative method for reservoir quality mapping based on sedimentary facies is proved to be more efficient and cost-saving in other development wells and aids updating and refining sedimentary model from seismic inversion. Multi-well correlation of sedimentary facies and sandbody orientation also provides strong support for subsequent designing of development wells location and secures better EOR by optimizing and adjusting the development plans.
Liu et al. (Mon,) studied this question.