Architecture Analysis And Remaining Oil Distribution Of Braided River Reservoir In Lamadian Oilfield

Fluvial sand bodies are important reservoirs for oil and gas.Braided river,as one of fluvial reservoirs,has the characteristics of poor channel stability,frequent lateral swings,rapid sand body plane facies change,complex sand body superposition relations,and strong heterogeneity.In the high-ultra high water cut stage,the oilfields have fully entered into a low-speed and lowefficiency development state.However,there is still a considerable amount of remaining oil that has not been recovered.These remaining oil plays an important role in improving oil recovery rate and delaying the pressure of production decline in old oilfields.And the fine characterization of reservoir architecture is an important means to re-understand the structure of complex fluvial sand bodies and further tap the potential of remaining oil.Taking the braided river sand body of Putaohua reservoir in Lamadian Oilfield as the research object,this thesis comprehensively utilizes multi-scale data such as cores,well loggings,field outcrops,modern deposits and production data,and adopts hierarchy analysis to study the structure according to the architecture classification scheme.The sand body architecture was dissected with the focus on the analysis of mid-channel bar and its internal structure and physical property distribution,and the braided river reservoir architecture model was established.Then,the automatic identification method of architecture elements was explored based on support vector machine.The growth,migration and evolution of the midchannel bar was analyzed using sedimentary numerical simulation,combined with modern deposits.Finally,thesis discussed the remaining oil distribution controlling by the architecture based on the three-dimensional geological model.These above researches are expected to provide a reliable theoretical basis for oilfields to tap the potential of remaining oil.Based on the investigation of the regional structure and sedimentary background,the target layers were re-determined using high-resolution sequence stratigraphy with stable distribution mark layer.Seven types of braided river lithofacies were identified in the process of architecture characterization.And the petro-electric characteristics of the third to fifth-order architecture boundary surfaces and its corresponding architecture units were analyzed based on the architecture classification scheme.The plane distribution of the four-order architecture units is established through the principles of vertical staging and lateral demarcation.With the rise of the base level and the increase of the A/S ratio,the main body of the channel with large thickness and wide distribution in the early period shrank and migrated to the northwest,the size of channel sand body decreased accordingly.The rise of the base level and the small annual average discharge led to a wide range of fluctuations in the depth and width and the stability deterioration of the channels.According to the analysis of internal structure of mid-channel bars,a single bar was identified up to four periods of the vertical accretion defined by the falling silty layers.The anatomy of modern deposits and subsurface reservoir revealed that the development positions of the falling silty layers were mainly in the main body,wings and tail of the mid-channel bars,while the head of the bars were barely developed.And the dip angle of the falling silty layers at the bar wings were obviously larger than that at other parts,with a maximum of 4.94°.The internal physical property analysis results of the mid-channel bar showed that the top permeability of the early accretion body was usually lower than the bottom permeability of next period accretion body among adjacent two periods of accretions.Eight modern braided river deposits from different river systems in the world were selected for this research.The geometric parameters of various architecture elements in the river were counted by multiple measuring points,and the quantitative relationship between the parameters was established.Statistical results show that the parameters of length,width and thickness of the mid-channel bar in the bifurcated braided river have stronger convergence and correlation than that of the wandering braided river.The geological knowledge base of the geometric parameters of the mid-channel bar was established by integrating modern deposits,outcrops and subsurface reservoirs.Finally,a braided river architecture model was established on the basis of the above architecture analysis.Considering the current situation of large well data and low efficiency manual architecture identification in the dense well pattern area,support vector machine(SVM)was used in this thesis to train different logging data sample sets.Combined with data dimensionality reduction of principal component analysis(PCA)and the parameter optimization,the automatic identification of architecture elements was carried out,with the identification accuracy reaching91.09%,which can basically meet the geological needs.Based on the architecture anatomy,in order to study the growth and evolution characteristics of the mid-channel bar,the Delft3 D hydrodynamic simulation software was used to carry out the numerical simulation of the braided river sedimentary dynamics.The simulation results showed that the growth of the mid-channel bar can be divided into early,middle and late stages,which was homologous to the three phases of the embryo,growth and migration,and complex of bar,and corresponded well to the modern deposits migration law of the mid-channel bar.The asymmetric flow on both sides of the bar was the main reason for the above changes.The growth and evolution model of the mid-channel bar was established according to the abovementioned bar body change law.According to the results of reservoir architecture anatomy,and with the guide of braided river sedimentary model,the three-dimensional geological model and attribute model based on the constraints of architectural elements were established.Combined with the numerical reservoir simulation and core test data,the F-Score value and SVM feature weight confirmed that the frequency and area of interlayers are the main factors controlling the remaining oil distribution.After the analysis of different levels of architectures,it showed that superimposed part of the fourth-order architectural units,the top of the positive rhythm layer,the tail and wing of bar,and the lower of falling silty layers were enrichment areas of remaining oil.