Flow Unit Model of Channel Sand Body and Its Effect on Remnant Oil Distribution: A Case Study of PI Formation in the Eastern Transition Zone of Daqing Oilfield

Abstract

To analyze the effect of various flow units in a channel sand body on remnant oil, we established a connection between various flow unit types and the remnant oil distribution. Using stratigraphic correlation and the characterization of sedimentary microfacies, we describe a single sand body, point bar, and narrow channel located at the injection-production well pattern of well B2-60-FB271 in the Eastern transition zone of the Daqing Placanticline. Architecture models of the point bar and narrow channel are also established using a series of parameters from different measurement methods. Four types of flow units (strong-current limiting, medium-current limiting, weak-current limiting, and none-current limiting) in the point bar sand body were identified, whereas one type, unshielded unit, was identified in the narrow channel. Geological parameters, such as porosity, permeability, and pore-throat radius (r50), were optimized to quantitatively characterize these various flow units. Samples were obtained from well B2-60-FB271 and analyzed by the freeze-fluorescence thin section technique. According to the displacement degree, the microscopic remnant oil was divided into three types: (1) free-state remnant oil, (2) semi-free-state remnant oil, and (3) bound-state remnant oil. We found that the strong-current limiting flow unit in the point bar is the enrichment area of free-state microscopic remnant oil and that the medium-current limiting and weak-current limiting flow units also have relatively high free microscopic remnant oil. These constitute the remaining oil enrichment areas in the study area.

Sedimentation of open-framework gravels in alluvial-fan settings: Quaternary Poplar Fan, northwest China

“…In the type 1 and 2 OFGs, due to the lack of internal heterogeneities that can act as flow baffles, no or little residual oil remains after primary development. However, in the type 4 and 5 OFGs, more residual oil may be present due to the occurrence of cross-bedding where the injection water cannot reach due to petrophysical heterogeneity determined by textural variations (alternation of volumes with occluded and openwork frameworks) that cause poorer sweep efficiency (Ma et al, 1999;Miall, 2014;Zhang et al, 2020b). The identification of a specific type of open-framework conglomerate may be rendered difficult where these are poorly cemented and tend to disaggregate into loose clasts in core; in these cases, the possible origin of the OFGs can be suggested based on the characteristics of adjacent and genetically related deposits, and based on knowledge of trends in processes across fan sectors.…”