| The main reservoir space of shale includes pores and fractures.Natural fractures are important reservoir spaces and main seepage channels of shale reservoirs,which control the migration,enrichment and single well productivity of shale oil and gas.The industrial oil flow has been found in the shale reservoirs of upper Es4 and lower Es3 members in Dongying Depression.However,there is still a problem of unclear understanding of the types and development rules of shale fractures in upper Es4 and lower Es3 members in Dongying Depression.Based on this,this paper has carried out the research on the characteristics of shale reservoir fractures.Based on the observation of cores and thin sections from 10 shale oil Wells in the study area at different scales and statistical analysis of a large number of experimental data,the fracture types were classified,the fracture development model was established,and the comprehensive evaluation of fractures was carried out based on lithofacies.The following results and understandings have been obtained:The classification and characteristics of reservoir space were studied.There are mainly two kinds of pores and fractures in the target interval.Pores include intergranular pores,intragranular pores,intercrystalline pores and organic pores.Fractures are divided into diagenetic fractures and tectonic fractures according to their origin.Diagenetic fractures include natural fluid pressure fractures,sedimentary-diagenetic fractures and shrinkage fractures.The fluid pressure fractures include bed-parallel fractures,bed-tranversing fractures and hydrocarbon generation and expulsion fractures.Structural fractures include shear fractures and tensile fractures.Natural fluid pressure fractures and deposition-diagenetic fractures are the main fracture types in the study area.The quantitative characterization of fractures was carried out.Fracture density,dip angle,opening degree and filling degree are taken as fracture characterization parameters.Accordingly,quantitative characterization of fracture characteristics based on lithofacies in wells was carried out.Different types of the characteristics of the development,opening and filling degree are different in different lithofacies.The fractures of organic-rich sparry calcite veined calcareous mudstone facies are the most developed,where they mainly occur as bed-parallel style with the highest linear density being 50/m.Fractures are not common in laminated silty mudstone facies and massive calcareous mudstone facies.The main controlling factors of fracture development in the study area are studied.It is considered that lithofacies,diagenesis,abnormal pressure and tectonism are the main controlling factors of fracture development.The lamellar and page-like structures are favorable to the development of fractures.The higher the content of brittle minerals is the more fracture develop.Different diagenesis types have different effects on fracture development.Abnormal pressure promotes fracture development;Faults affect the development of structural fractures.Four typical fracture development models in different lithofacies are established.The fracture development characteristics evaluation based on lithofacies is carried out.The paper selects the parameters of fracture,diagenesis,brittleness index,TOC,Ro,hydrocarbon generation potential,etc.,and evaluates the fracture development characteristics based on different lithofacies by entropy weight method.The fractures are divided into three types,I,II and III,which correspond to good,medium and poor.Based on this,the fracture development of single well was evaluated in Nx55,W78 and Ny1 well. |
