| The exploration and development for Ordovician WuFeng Formation to Silurian Longmaxi Formation,Sichuan basin has been made a significant breakthrough and progress in recent years,and a central investigation on shale gas within the basin also has been broken from the dawn.The relations between fractured range and fracturing construction evidence in stimulation treatment to the shale reservoir and reservoir characteristics were included in current research.Nevertheless,the research on reservoir characteristics and formation mechanism of network in reservoir cannot be well-collaborated,thus restricting the effective development of shale in WuFeng Fm.to Longmaxi Fm.In this regard,based on the shale lithofacies developmental characteristics in the 1st member of WuFeng Fm.to Silurian Longmaxi Fm.at southwest Sichuan with the geological exploration data,this paper provides a delicate and systematical investigation on geologic features of shale reservoir and the geological influence mechanism on the formation of reservoir network guided by the discipline theory of sedimentary petrography,reservoir geology,sequence stratigraphy and geophysics etc.and its extending methodology on a basis of existing data and research findings,and further presents an analysis and quantification results on the relations between plurals affecting mechanism based on statistics,Hertz elasticity contact theory,fracture mechanics,stress-strain model of porous media etc.by the investigation on the control mechanism by sedimentary Processes and diagenesis,from which a evaluation method for the complex fracability of shale reservoir network.An accurate evaluation on the shale gas well(section)was made by an analytical focus on wells in Jiaosiba shale gas field.The research findings are shown as fellows:(1)Study on reservoir characteristics and sequence stratigraphy we have found the vertical differences from mineral components,electrical and geochemistry properties between Wufeng Formation to Longmaxi Formation under the control of the identified sequences and the main function of deposition and diagenesis for shale reservoir's differential development.Based on dissimilitude about mineral components,facies frequency and micro-fractures scale,the shale reservoir can be divided into 6 types of microfacies such as siliceous and high argillaceous shale facies(F1),argillaceous and high siliceous shale facies(F2),calcareous and low siliceous facies(F3),calcareous and high siliceous facies(F4),mixed shale facies(F5)and high authigenic siliceous shale facies(F6).The scheme can lay the foundation for subsequent research on mesoscale facies association identification and comprehensive network fracability evaluation.(2)Sections and wells' delicate description have done which based on mesoscale stratigraphy analysis.We systematically study the transformation of shale gas reservoir development under the control of the eustasy and terrigenous injection.We proposed that there are the rhythmic discipline in vertical development in shale gas reservoir and distinction in different sedimentary period or same sequence.Then we indicated that shale reservoirs in Wufeng Fm and Longmaxi Fm had various influences in fracturing network forming period.(3)We proposed that mineral components,natural fractures,reservoir properties and lamellation can be treated as the main factors by comprehensively analyzing the influences to shale gas reservoir fracture-network forming and frac-type,interbed-type and bio-type shale facies association can be identified.Some similarities have been possessed between shale gas reservoir and conventional reservoir,so we found the vertical evolutionary trend form frac-type to interbed-type to bio-type in shale.Then we finished the study on evolution law on the fracture network factors above and proposed the vertical and horizontal relationships among the facies associations would influence the effect to form the fracture-network in hydraulic fracturing process from Wufeng Fm to Longmaxi Fm by reservoir and geochemistry data.(4)The response between litho-mechanics and deposition&diagenesis has been studied based on the reservoir characteristics research.The interactions and connections in each fracture-network geological factors have been discussed.We pointed out that fracture-network result would be influenced by mineral components proportion,contact relationship in each mineral,interactions between natural fractures and laminations under the control of facies,pore scale in porous medium and the fracture-network comprehensive evaluation should be divided into reservoir properties and fracability evaluation.(5)For choosing the "geological sweet spot" with high quality properties and "man-made transfusion zone" with large SRV in the meanwhile to achieve "Full scale volume fracturing",the reservoir evaluation index,fracability evaluation index,fractures index can be established based on differential effective medium theory and facies-controlled theory.From this,The fracture-network comprehensive evaluation model(Ec)can be established to identify the superior shale with high quality properties and large SRV when the Ec is distributed with values ranging from 0.45 to 0.5 and secondary superior shale when the Ec is higher than 0.5.To sum up in conclusion,the shale gas reservoir fracturing selection scheme in Wufeng Fm and Longmaxi Fm has been proposed. |
PDF Full Text Request