Genesis and control factors of shale oil reserving space in Dongying sag

The reserving spaces of mud shale reservoirs in faulted lake basin are diversified, of which the genesis and control factors are relatively complicated. A study was conducted on the mud-shale development horizons of Lower Sub-member 3-Upper Sub-member 4 in Paleogene Shahejie Formation, Dongying sag, Bohai Bay Basin. By means of X-ray diffraction whole-rock mineral analysis, rock thin section and scanning electron microscopy technologies, as well as major trace element test and organic geochemical test data, the basic characteristics of mud shale reservoirs were confirmed. Based on the identification of reserving space types and basic characteristic descriptions, the genetic classification scheme of reserving space in mud shale of Dongying sag was established; the critical geological mechanism affecting the development of reserving space was also deeply analyzed. The research results show that: (1) the mud shale of Dongying sag is characterized by diversified architecture minerals and rock types, extremely strong reservoir heterogeneity, high abundance of organic matter (TOC is mainly ranged between 1.2% and 6.7%), low maturity (Ro value is dominantly in the range of 0.51%-0.89%), the porosity of 2.9%-9.8%, vertical permeability of 0.003 40-0.578 mD and complex pore structure; (2) in terms of genesis and development abundance, the important reserving space types include clay-mineral flocculent pores, clay-mineral contraction fractures, intergranular pores in recrystallized calcite, dolomitized intergranular pores, organic-matter contraction micro fissures, carbonate dissolution pores, abnormal high pressure fissures and inter-layer micro fractures; (3) sedimentary microfacies plays a control role in the component, composition fabric and plane distribution of pore framework mineral, and the lake salinization degree influenced by climate makes an impact on the vertical superimposed mixture mode of fine grains, so as to further control the types and assemblages of reserving space; (4) in different salinization stages, the formation and evolution of secondary pores are controlled by the diagenetic fluid properties, changes of authigenic minerals such as carbonate and clay, as well as organic-matter hydrocarbon generation and evolution. Calcite recrystallization, clay mineral reaction and transformation, dissolution and organic-matter hydrocarbon generation function are important diagenesis types controlling the development of reserving space. © 2016, Editorial Office of ACTA PETROLEI SINICA. All right reserved.