Numerical Simulation Study On Dual Laterolog Response Of Tight Sandstone Fracture Filling Degree

Tight sandstone reservoirs are the focus of exploration and development of unconventional oil and gas fields,and fractures are one of the important reservoir spaces and seepage channels for oil and gas.The identification and research of fractures in tight sandstone reservoirs is of great significance.The size,occurrence and filling degree of fracture development all make the logging response more complicated.As a commonly used electrical logging method,dual laterolog is more sensitive to the response of reservoir fractures and can also reflect rich formation information.In the practice and research of fractured tight sandstone reservoirs,it is found that the fractures usually have mineral filling characteristics,but the current related research is not perfect,which interferes with the identification and evaluation of the dual laterolog of the fractures.Numerical simulation studies the response characteristics of dual laterolog of fractures with different filling degrees and analyzes the response characteristics and influencing factors.Firstly,a dual laterolog tool model and a fractured formation model with different filling degrees are established.Combined with the structure of the commonly used dual laterolog tools,set relevant specifications and parameters of the tools;combined with the practical work and investigation of fractured tight sandstone reservoirs,the common mineral filling characteristics of tight sandstone fractures are analyzed,and fracture formation models with different filling degrees are constructed.The fracture model is as follows: For plate-shaped fractures,fillers are filled on one side of the fractures in the form of “vein-like” and parallel occurrences,and relevant parameters such as filling mineral thickness and resistivity are set.Then,using the finite element method,the forward modeling scheme and boundary conditions of the dual laterolog tool are established,and the electrode coefficients of the dual laterolog tool model are calculated and tested.In the fractured formation model,based on the working principle of the dual laterolog tool,the The potential of the solution area is simulated and calculated,and the potential on the supervision electrode is obtained,and then the apparent resistivity of the deep and shallow lateral directions at different depths is simulated and calculated,and its reliability is verified by the analytical algorithm.Furthermore,the dual-lateral logging response characteristics of a single flat fracture with different filling minerals,as well as the effect of fracture width and dip angle on the duallateral logging response of partially filled fractures,were studied,focusing on the duallateral logging response of the fracture filling degree.Log response characteristics,comparing the dual lateral log response characteristics and the difference of deep and shallow laterals for unfilled,partially filled and fully filled fractures,as well as the influence of filling mineral types.The results show that within the effective detection range of the instrument,with the increase of the fracture width,the depth and depth of the low-resistivity mineral filling is obviously different from that of the high-resistance mineral filling;The law of "negative anomaly" of angle fractures;if the fractures are effective(not 100% filled),the filling minerals do not change the "trend" of the response change of the dual laterolog,but only affect the amplitude.The dual laterolog response characteristics and understanding of the tight sandstone fracture filling degree obtained from the study provide a set of methods and technical support for the identification and evaluation of fractured reservoirs.