Abstract The architecture of sandy braided rivers, especially the mid-channel bars and the internal intercalations, plays a key role in the enhancement of remaining oil. Based on ancient outcrops, modern deposits and geological models, taken P oilfield as an example, this paper studies the different hierarchies of the internal architectural elements to describe the heterogeneity of sandy braided fluvial reservoir qualitatively and quantitatively, and proposes techniques to characterize the architecture of underground braided fluvial reservoirs. Based on the proposed distribution pattern and the related characterization techniques, the different controls of architecture elements on the distribution of remaining oil are analyzed: (1) sandy braided rivers have three filling patterns, dominated by sandy fillings. The mid-channel bars and braided channels are distributed in the pattern of wide bars and narrow channels, while the silting layers within mid-channel bars have dome-like and horizon-like distribution patterns; (2) the architectures are characterized from 5th to 3rd-order hierarchies successively under the principle of thickness control, scale constraint and multidimensional interaction. Single braided belts can be classified by three identification marks (the average width/thickness ratio is about 178, the width ratio of braided channels and mid-channel bars is about 1:3.8, and the width/length ratio of mid-channel bars is about 1:2.2); (3)Single-period silting layers are nearly horizontally distributed within mid-channel bars and multi-period ones are parallel with each other, generally 2-4 silting layers; (4)Reservoir architectural elements of different hierarchies exert different controls on the distribution of remaining oil. The intercalations control the remaining oil directly in the hierarchy of braided belts. In the hierarchy of mid-channel bars, semi-muddy filling channels have enriched in remaining oil due to relatively poor watered out degree as a result of disconnected sand bodies in the upper part with connected sand bodies in the lower part. Influenced by silting layers and petrophysical boundaries, the remaining oil within mid-channel bars is mainly distributed as “segment-like” enrichment at the top of vertical aggraded bodies under the silting layers and at the margin of poor water flooding. Overall, the research not only has good applications in the integral adjustment schemes of mature wells and development designs of news wells in oilfields, but also provides geological basis for well deployment of adjusting wells, especially for producing remaining oil in horizontal wells.
Microbial community samples have been accumulating at a speed faster than ever, with hundreds of thousands of samples been sequenced each year. Mining such a huge amount of multisource heterogeneous data is becoming an increasingly difficult challenge, so efficient and accurate compare and search of samples is in urgent need: faced with millions of samples in the data repository, traditional sample comparison and search approaches fall short in speed and accuracy.
The PL 19–3 Oilfield is the only super-large monolithic oilfield with oil and gas reserves up to 1 × 109 t in the Bohai Bay Basin, and it has been successfully developed. Exploration and development practices have provided abundant data for analyzing formation conditions of this super-large oilfield. On the basis of the exploration and development history, fundamental reservoir features, and with available geological, geophysical and test data, the hydrocarbon accumulation conditions and key exploration & development technologies of the PL 19–3 Oilfield were discussed. The key conditions for forming the super-large Neogene oilfield include four aspects. Firstly, the oilfield is located at the high position of the uplift that contacts the brachy-axis of the multi-ridge slope in the biggest hydrocarbon-rich sag in the Bohai Bay Basin, thus it has sufficient hydrocarbon source and extremely superior hydrocarbon migration condition. Secondly, the large-scale torsional anticlines which formed in the Neogene under the control of the Tanlu strike-slipping movement provide sufficient storage spaces for oil and gas preservation. Thirdly, the "multiple sets of composite reservoir-caprock assemblages" developing in the special shallow-water delta further contributes greatly to the effective storage space for oil and gas preservation. Fourthly, due to the coupling of the uplift and strike slip in the neotectonic period, extensive faulting activities constantly released the pressure while the late period massive hydrocarbon expulsion of the Bozhong took place at the same time, which assures the constant and intense charging of oil and gas. The super-large PL 19–3 Oilfield was controlled by the coupling effects of all those special geologic factors. In view of this oilfield's features (e.g. violently reformation caused by strike slip, and the special sedimentary environment of shallow-water delta), some key practical technologies for exploration and development have been developed. Such technologies include: the special prestack depth migration processing for gas cloud zones, the prediction of thin interbed reservoirs based on high-precision inversion of geologic model, the reservoir description for the shallow-water braided river delta, the quantitative description for remaining oil in the commingled oil reservoirs with wide well spacing and long well interval, and the well pattern adjustment for formations during high water cut period in the complex fluvial-facies oilfields.
Based on study on the main factors affecting the initial productivity of directional wells in multilayer sandstone reservoirs of Penglai 19-3 oil field, a permeability interpretation model based on lithofacies constraint was established, and an initial productivity prediction formula for directional wells in offshore multilayer sandstone reservoirs was derived. Permeability and oil saturation are the main factors affecting initial productivity of directional wells in Penglai 19-3 oil field. Using core, scanning electron microscope, casting thin section, logging and production data, and a new permeability interpretation model considering the influence of macro sedimentary characteristics and microscopic pore structure was built. On the basis of permeability correction, resistivity increase ratio is introduced to characterize the effect of oil saturation, to modify the Vandervlis productivity formula of directional wells to get an initial productivity prediction equation suitable for continental multilayer sandstone reservoirs. The study results show that the permeability considering petrographic constraints and the production forecasting formula including resistivity increase ratio are more accurate.
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