Construction of a fluvial facies knowledge graph and its application in sedimentary facies identification

Lithofacies paleogeography is a data-intensive discipline that involves the interpretation and compilation of sedimentary facies.Traditional sedimentary facies analysis is a labor-intensive task with the added complexity of using unstructured knowledge and unstandardized terminology.Therefore,it is very difficult for beginners or non-geology scholars who lack a systematic knowledge and experience in sedimentary facies analysis.These hurdles could be partly alleviated by having a standardized,structured,and systematic knowledge base coupled with an efficient automatic machine-assisted sedimentary facies identification system.To this end,this study constructed a knowledge system for fluvial facies and carried out knowledge representation.Components include a domain knowledge graph for types of fluvial facies(meandering,braided and other fluvial depositional environments)and their characteristic features(bedforms,grain size distribution,etc.)with visualization,a method for query and retrieval on a graph database platform,a hierarchical knowledge tree-structure,a data-mining clustering algorithm for machineanalysis of publication texts,and an algorithm model for this area of sedimentary facies reasoning.The underlying sedimentary facies identification and knowledge reasoning system is based on expert experience and synthesis of publications.For testing,17 sets literature publications data that included details of sedimentary facies data(bedforms,grain sizes,etc.)were submitted to the artificial intelligence model,then compared and validated.This testing set of automated reasoning results yielded an interpretation accuracy of about 90%relative to the published interpretations in those papers.Therefore,the model and algorithm provide an efficient and automated reasoning technology,which provides a new approach and route for the rapid and intelligent identification of other types of sedimentary facies from literature data or direct use in the field.

Fluvial facies reservoir productivity prediction method based on principal component analysis and artificial neural network

It is difficult to forecast the well productivity because of the complexity of vertical and horizontal developments in fluvial facies reservoir.This paper proposes a method based on Principal Component Analysis and Artificial Neural Network to predict well productivity of fluvial facies reservoir.The method summarizes the statistical reservoir factors and engineering factors that affect the well productivity,extracts information by applying the principal component analysis method and approximates arbitrary functions of the neural network to realize an accurate and efficient prediction on the fluvial facies reservoir well productivity.This method provides an effective way for forecasting the productivity of fluvial facies reservoir which is affected by multifactors and complex mechanism.The study result shows that this method is a practical,effective,accurate and indirect productivity forecast method and is suitable for field application.

The Pliocene-Recent Euphrates river system:Sediment facies and architecture as an analogue for subsurface reservoirs

The Tigris-Euphrates is a continental-scale fluvial system,around 2800 km in length,which drains over 1 million km2 of SWAsia.The system originated in the Late Miocene and developed into the principal axial drainage system of the region,which follows broad regional structural features of the Mesopotamian Foreland Basin.Good preservation and outcropping of the Pliocene and Quaternary Euphrates deposits yield a viable local analogue for subsurface fluvial reservoirs in the region,and for other fluvial systems that have developed in foreland basin settings.This paper documents the first detailed study of the sedimentary characteristics of these Pliocene and Quaternary fluvial deposits along the middle reaches of the present-day Euphrates in Syria.The Euphrates fluvial system developed from small and probably short-lived isolated cut-and-fill channels in the Pliocene,characterised by abundant debrite and slump facies,through to a broad meandering system at present.The Quaternary deposits represent a braided to meandering system that was more energetic than that of the modern day Euphrates.The Quaternary facies include a dominance of gravels,pebbly sands and sands as channel associations,coupled with sands,muds and paleosols representing channel abandonment,overbank and crevasse-splay associations.Channel widths,where observed,range from 50 to 500 m,and minimum fill thicknesses range from 3 to 7 m.The combined channel-fill for stacked channels is up to 25 m thick.Lateral correlation of channel elements over at least 1 km of section indicates that rapid and extensive lateral migration has occurred.Crevasse splay lobes can be identified in the overbank deposits,with a width of 30e60 m and sand thickness of 0.5e1.5 m.The geometry,nature and dimensions of these architectural elements provide a useful analogue for subsurface reservoirs.The high-energy channel facies of the Quaternary system show very good reservoir attributes,with good correlation and connectivity.At the bed-scale there is significant heterogeneity of characteristics that would impact fluid-flow for hydrocarbon production from a subsurface reservoir.However,incomplete preservation of these Quaternary fluvial deposits at outcrop remains a challenge for accurately determining the scale of sedimentary features and also the size of the paleo-river.

Study on Development Law of Complex Fluvial Reservoir under Water

The Bozhong oilfield (Hereinafter referred to as BZ oilfield) is a typical representative of complex fluvial reservoirs in the Bohai Sea, located in the southern Bohai Sea, with an average porosity of 30.3% and an average permeability of 643 × 10-3 μm2, belonging to medium high porosity and permeability reservoir, the reservoir has good connectivity, and the average underground crude oil viscosity is 5 mPa·s. There are many plane fault blocks, and the longitudinal oil well section is long, so the oil-water relationship is very complex. With the further development of the oilfield, the vertical and horizontal oil-water movement law, residual oil distribution and potential are unclear, resulting in rapid bottom water coning, unbalanced injection and production in the oilfield, and increasingly prominent contradictions among layers, planes and layers in the oilfield. Through numerical simulation analysis and comparison of displacement law and recovery degree under different influence conditions, this paper studies the development effect of actual sand body under different influence conditions such as different well types, different development methods and well layout positions, and takes appropriate development methods for the oilfield, which is of great significance to improve the development effect of the oilfield.

Study on Quantitative Prediction Method of Interlayer Based on Seismic Waveform

Taking the fluvial reservoir of the Neogene Minghuazhen Formation in Bozhong S oilfield in China as an example, a detailed study of the interlayer in the reservoir was conducted. From the perspective of sedimentary genesis of the interlayer, three types of genesis of the interlayer are summarized and analyzed, namely, fine grain sediment in the inter peak channel, suspended sediment in the post flood channel, and abandoned channel sediment. At the same time, combined with seismic waveform analysis, the distribution characteristics and morphology of the interlayer in complex fluvial facies oilfield are carefully depicted, and the horizontal well optimization implementation is guided based on the planar and three-dimensional spatial distribution characteristics of the interlayer. This method enriches the characterization technology of interlayer in offshore oilfields, and has important guiding significance for the overall evaluation and development research of complex fluvial facies oilfields.

Development Strategies for Achieving High Production with Fewer Wells in Conventional Offshore Heavy Oil Fields in Bohai Bay,China

Development strategy for heavy-oil reservoirs is one of the important research interests in China National Offshore Oil Corp. （CNOOC） that plans a highly effective development for heavy oil fields in multilayered fluvial reservoirs because of their significant influence on marine oil and even on China＇s petroleum production. The characteristics analysis of multilayered fluvial reservoirs in the heavy oil fields in Bohai Bay indicates that large amounts ofoil were trapped in the channel, point bar and channel bar sands. The reserves distribution of 8 oilfields illustrates that the reserves trapped in the main sands, which is 20%-40% of all of the sand bodies, account for 70%-90% of total reserves of the heavy oil fields. The cumulative production from high productivity wells （50% of the total wells） was 75%-90% of the production of the overall oilfield, while only 3%-10% of the total production was from the low productivity wells （30% of the total wells）. And the high productivity wells were drilled in the sands with high reserves abundance. Based on the above information the development strategy was proposed, which includes reserves production planning, selection of well configuration, productivity design, and development modification at different stages.

A microscopic ancient river channel identification method based on maximum entropy principle and Wigner-Ville Distribution and its application

In view of the problem of fine characterization of narrow and thin channels,the maximum entropy criterion is used to enhance the focusing characteristics of Wigner-Ville Distribution.On the basis of effectively improving the time-frequency resolution of seismic signal,a new method of microscopic ancient river channel identification is established.Based on the principle of the equivalence between the maximum entropy power spectrum and the AR model power spectrum,the prediction error and the autoregression coefficient of AR model are obtained using the Burg algorithm and Levinson-Durbin recurrence rule.Under the condition of the first derivative of autocorrelation function being 0,the Wigner-Ville Distribution of seismic signal is calculated,and the Wigner-Ville Distribution time-frequency power spectrum(MEWVD)is obtained under the maxi-mum entropy criterion of the microscopic ancient river channel.Through analysis of emulational seismic signal and forward numerical simulation signal of narrow thin model,it is found that MEWVD can effectively avoid the interference of cross term of Wigner-Ville Distribution,and obtain more accurate spectral characteristics than STFT and CWT signal analysis methods.It is also proved that the narrow and thin river channels of different scales can be identified effectively by MEWVD of different frequencies.The method is applied to the third member of Jurassic Shaximiao Formation(J2s33-2)gas reservoir of the Zhongji-ang gas field in Sichuan Basin.The spatial information of width and direction of narrow and thin river channels with width less than 500 m and sandstone thickness less than 35 m is accurately identified,providing bases for well deployment and horizontal well fracturing section selection.