Laboratory Study On Wave Field Characteristics In Low Porosity Double-porosity Physical Models

In unconventional reservoirs,Fractures are important for oil and gas migration and storage.Experimental researches on how fractures affect seismic wave velocity and anisotropy in low porosity condition have great significance.By adjusting the sorting of silica grains,choosing materials with good thermostability,increasing the pressure,the porosity of the double-porosity model was decreased.Measures include adjusting the portion of materials,cutting the model into several parts to sinter,and slow heating were taken to avoid the cracking of the model.A set of tools were made in order to increase the speed and stability of the manufacturing process.Parameters like porosity and fracture density can be controlled well in the model.A group of fractured models with similar fracture density and different porosity from 15.4% to 30% were made to investigate the impact of fractures on P and S wave velocity anisotropy in different porosity condition.The experimental data were compared with results of Hudson and Thomsen theoretical model.Several results were found: a)P wave anisotropy shows a decreasing trend with the increase of porosity in water saturated condition.b)In the direction parallel to fracture plans,measured SWS coefficient fits the both theoretical predictions,and insensitive to porosity.c)In the direction of 45°to the fracture normal,SWS coefficient decreases with the increase of porosity.