Reservoir characteristics and control factors of Tongbomiao formation in Hongqi sag

Hongqi sag is located in the north of Beiehur depression in Hailar Basin, which is a secondary structural unit in the peripheral depression of Hailar Basin, with great exploration potential. Based on SEM, conventional thin sheet, cast thin sheet, mercury pressure and physical property data, this paper discusses the reservoir characteristics, types and control factors of high quality reservoir in Tongbomiao formation, Hongqi sag, so as to provide a strong geological basis for the exploration of oil and gas in this area. The reservoir space of Hongqi sag is mainly composed of four types: primary intergranular pore, micro fracture, feldspar dissolution pore and debris dissolution pore. It is of the type of ultra low porosity and low permeability. Although Tongbomiao formation in Hongqi sag is of very low porosity and low permeability type, high quality reservoir is still developed, and its reason is mainly controlled by sedimentary environment, diagenesis and structural fracture.

A near-shore clastic-carbonate mixing mode in a continental rift basin (early Oligocene, eastern Shijiutuo Uplift, Bohai Bay Basin, China): sedimentology, reservoir characteristics and exploration practice

A comprehensive sedimentary and reservoir analysis was conducted based on seismic, well logging, core and relative test data, taking Members 1 and 2 of Shahejie Formation of the early Oligocene in the steep slope belt, eastern Shijiutuo Uplift (STU), Bohai Bay Basin (BBB) as a case. The study indicates that a near-shore mixed fan deposit formed in the study area and developed characteristics and pattern of a high-quality reservoir. The mixed clastic-carbonate rocks constitute Members 1 and 2 of Shahejie Formation which developed along the steep slope belt and is named as a near-shore mixed fan. The mixed fan of the study area is mainly composed of microfacies of proximal channel, mixed deposited channel, mixed clastic beach, mixed bioclastic (grain) beach, with vertical multi-stage superimposition feature, and basically a similar shape as modern near-shore fans. It constitutes a new depositional type developing in the steep slope belt of a characteristic and complex lacustrine rift basin in the study area. This mixed fan in the steep slope of eastern STU is controlled by comprehensive factors including tectonics, clastic material supply, climate, palaeogeomorphology and hydrodynamic conditions. The reservoir quality of Members 1 and 2 of Shahejie Formation of eastern STU is, however, actually controlled by the sedimentary environment and diagenesis processes. Coarse-grained mixed rocks of near-shore fans, rich in bioclastics, can form excellent reservoirs, characterized by resistance to compaction, easy to dissolution, little influenced by burial depth and high production of oil and gas, which enable them become key exploration targets of medium-deep strata of BBB. Analyses of high-quality reservoir, its controlling factors and the oil and gas exploration implications of the near-shore mixed fan developing in the study area give a deeper insight into discussions of the same type of mixed rocks of other lacustrine rift basins worldwide.

Potential hydrocarbon reservoirs of Albian–Paleocene age in the Nuussuaq Basin, West Greenland

The onshore Nuussuaq Basin in West Greenland is important for hydrocarbon exploration since many of the key petroleum systems components are well exposed and accessible for study. The basin has thus long served as an analogue for offshore exploration. The discovery of oil seeps on Disko, Nuussuaq, Ubekendt Ejland, and Svartenhuk Halvø (Fig. 1) in the early 1990s resulted in exploration onshore as well. In several wells, oil stains were observed in both the siliciclastic sandstone and in the volcanic series. An important aspect of any petroleum system is a high quality reservoir rock. The aim of this paper is to review petrophysical aspects of the reservoir potential of key stratigraphic intervals within the Nuussuaq and West Greenland Basalt groups. Reservoir parameters and porosity–permeability trends for potential siliciclastic and volcanic reservoirs within the relevant formations of the Nuussuaq Basin are discussed below.