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An Integrated Modeling Approach for Multi-Scale Fault-Related Fractures in Tight Sandstone Reservoirs Based on Structural Control and Geomechanical Method


The distribution of fault arrays and fault-related natural fractures greatly improve the heterogeneity of reservoir matrix, and strongly influence the fluid flow. In consideration of the strongly irregular shape of natural fractures and the uncertainty of spatial distribution laws, guided by the actual geological pattern of study area, a matrix model and fracture model are established based on well log, seismic, core and rock mechanics data with the modeling method of finite element numerical simulation, ant tracking, discrete fracture network, and trend model. The fault scale model is established by seismic structural interpretation utilizing deterministic modeling method; the sand body scale model is established by core and well log interpretation and seismic horizon interpretation utilizing deterministic modeling and stochastic modeling method. For the model of natural fracture scale, discrete fracture network modeling method is used to model the natural fracture in different scales, which is divided into large, small-mid and scales. Taking the fracture modeling of the third member of the Paleogene Shahejie Formation tight sandstone in eastern china as a case study. On the basis of matrix model, by analyzing the relationship between natural fractures and fault from well log and core data, establishing the conceptual model between fracture density and fault damage zone, which show a decay trend. With the guidance of conceptual model, the large scale natural fracture model is established by ant tracking utilizing deterministic modeling; for small-mid scale natural fracture, firstly, a single well brittleness evaluation is established based on uniaxial compression, brazil split and triaxial compression experiment data; then the fracture density is identified and calculated through well log data; with the constraint of brittleness and sedimentary facies, a calibrated fracture density model of single well is established. With the lithofaices distribution as main driver, a 3D young’s modulus and brittleness index model are established based on rock mechanic experiments data. Additionally, the relationship between tectonic stress field and fracture parameters is quantitatively established by finite elements numerical simulation based on rock mechanic experiments. Taking the calibrated fracture density of single well as hard data, with constraint of conceptual model, the 3D brittleness index model and tectonic stress field is fitted utilizing trend modeling, which to form a 3D fracture density volume as soft data, then the discrete fracture network is established. By coupling the fracture model with the matrix model, fitting with dynamic data shows that the model has higher fitting consistency.

Key words: tight sandstone; discrete fracture network; fracture modeling; multi-scale; fault-related fracture; rock mechanic experiment; tectonic stress field; brittleness