Characterization Of Flow Units And Integrated Geological Modeling In Braided River Reservoirs

In view of the fact that braided river reservoirs are becoming more important in clasolite reservoirs at home and abroad,an intensive study is very necessary to carry out.H2 and H1 Members in Daniudi Field in Ordos Basin,with high productivity and abundance of gas,clearly identified as a depositional system of braided rivers,have so complex features in both deposition and diagenesis that the reservoirs are very heterogeneous,and distinguish themselves by the key feature of low porosity-low permeability,high reserves and low abundance.Since put in development in 2002,the field has accomplished 10×108m3/y productivity construction under the guidance of the recognitions that sedimentary facies control high quality reservoirs and the high quality reservoirs control the high productivity blocks.However,with the research development,it is becoming difficult to evaluate high-quality reservoirs only with sedimentary micro-facies,because the high- quality reservoirs are controlled not only by the sedimentary micro-facies,but also by diagenesis.Therefore,it has significant meaning to study the model of forming and the principle of distribution of braided river reservoirs for enriching the genetic theory of high quality reservoirs in braided river reservoirs and instructing the next step of productivity construction.Based on the achievements of microfacies,this paper makes a thorough analysis of the sand body of braided river from aspects of architectural units and fluid-flow unit.In addition,a 3D model of fluid-flow unit has been established based on geology,log and seismic integrately.At last,this paper analyzes the relationship among the architectural elements,flow units and productivity,and predicts the distribution of quality reservoirs.Meanwhile,an analysis process of heterogeneity of braided river reservoirs,which is multiple levels and comprehensive,has been established,which provides a new thought to study this kind of reservoirs.Through this research,two important results were obtained,which were the architecture of flow units in the genetic units of braided river and the relationship among the architectural elements,flow units and productivity.Take DK30-DK12 well block as an example,this paper analyzes the elemental features of braided reservoirs in H1 Member and H2 Member.The results of the research showed that although both of these two Members occurred in the channel bar facies,differences exist obviously.H1 Member forms in a beginning period when base level was rising,which lead to a result that channels are wild and shallow,changed frequently,and the main pattern of sand bodies are vertical stack with some lateral stack pattern.This kind of pattern contributes to phenomena that sand bodies distribute wildly and the heterogeneity is quite serious,single stage sand is not so thick,although the total thickness of sand is very thick.H2 Member forms in a later period when base level was rising.Compared to H1 Member,their W/T parameters are smaller and present a feature of low-sinuosity and meander.The main pattern of sand bodies is vertical stack with some lateral stack pattern.This kind of pattern contributes to phenomena that sand bodies don't distribute wildly and the heterogeneity is quite low,the total thickness of sand is relatively thin,but single stage sand is thicker.To depict the genetic unit of the braided river reservoirs amply,this paper applies the theory of architectural elements analysis to divide the braided reservoirs into four kinds of architectural units,which are channel unit(CH),sheet sand(SS),channel bar(CB),over bank(OB).This paper contrasts the differences of architectural units' features and log features between H1 Member,which is wild and thin,and H2 Member,which is narrow and thick.These differences lead to the disparity of the log featuresBased on the study of microfacies and architectural unit,the attributes of lithology,physical property and structure of porosity and throat were statisticed.Both of two Members show us some features that compositional maturity and texture maturity low is low,secondary pore is obvious,pore and throat structure is complex.According to the distribution of core porosity and the relationship between porosity and permeability,this paper defines 8%for porosity and 0.45mD for permeability as the bottom boundary of the high-quality reservoir.It is not difficult to find that the impaction of sedimentary is obvious which represented by the fact that the physical property of intra-channel is better than margin location of the channel.The architectural unit CH and architectural unit CB provide the best physical property,which is high-quality reservoir, while the physical property of architectural unit OB is bad,which is inefficient reservoir.In order to study the heterogeneity of architectural units thoroughly,this paper analysis adopts the method of flow units and refines the definition and study-process of flow units.Author hold that flow units can be researched though the study of architectural elements,although flow units don't belong to architectural-element system.There are two main aspects of study,one is the definition of surface boundary,and the other is the characterization of properties in the flow unit.Based on the discussion above,this paper established a research process for reservoir heterogeneity of braided river,which is layer-sedimentary microfacies-architectural elements-flow units.According to analysis results of core from work area,this paper proceed flow units division synthesizing the mind of normality secondary-population and clustering method,and classify A and B type as high-quality reservoir in these two Members.And then,this paper establish identification model of flow units using the technology of neuronic network and propose combination patterns of flow units in work area,which contain four major categories,16 sub-categories:homogeneous type,compound anti-cycle type(ABC type),compound positive cyclic type(CBA-type) and compound cycles type(ABCBA type).After analyzing combination patterns of flow units focused on the constitute units of CH and CB,it can be concluded that compound positive cyclic type and homogeneous type are the majority,while the other is compound cyclic type.On the basis of identification of flow units of non-coring well by using logging data, according to the modeling principle of hierarchical modeling,layer-by-layer control,primary determination and seismic constraints,integrating the results of geology research,logging, reservoir horizontal prediction by seismic,under the constraint of layer,sand framework, architectural elements and physical model step by step,3-D model of reservoir flow unit is established by the high-resolution of seismic in verticalness and logging in horizontalness.By means of analysis of distribution feature in profile and flat of flow units,it is easy to get the conclusion that H1 Member is poorer in physical property,and that high-quality reservoir(A and B type) in this Member is well consecutive in horizontal and badly communicated in verticalness, which shows the contribution of sedimentary factors to heterogeneity obviously.On the contrary, every flow unit in H2 Member is well in reservoir physical property,high-quality reservoirs(A and B type) in this Member is badly consecutive in horizontal and good connectivity in verticalness,showing the diagenesis effect to heterogeneity obviously.Based on the studies above,this paper analyzes and summarizes the relationship between architectural elements,flow-unit combination styles,and productivity.The measure showed that the CH and CB units are important reservoir types in the work area,but the variation in productivity between the two units is obvious.The deviations of flow unit combination pattern unit within the architectural elements lead to the difference of reservoir quality and then further affect productivity after deeper analysis of the flow units.Taken as a whole,productivity is relatively higher in the homogeneous A,B and compound cyclesⅡtypes.Finally,regarded to the gas-bearing,it is reviewed how heterogeneity factors,such as the combination style,sandstone thickness,laminated distribution and so on,will affect productivity by comparing and analyzing, and spatial distribution of high-quality reservoir is predicted in view of the discussion above.