Study On Tracer Flowback Interpretation Method For Multi-stage Fractured Horizontal Wells

The development of tight reservoirs has become a hot issue in the development of unconventional energy in China,and it is of great significance for China's energy reserves and national energy strategic security.At present,the development of tight reservoirs mainly relies on hydraulic fracturing technology,but the description of underground fracturing after hydraulic fracturing is still a more complicated issue.Currently,interpretation techniques such as production dynamic evaluation and micro-seismic monitoring technology have been used,These technologies have less accurate and shortcomings.In order to more accurately describe the shape of fracture shape after hydraulic fracturing operations,currently in field applications of reservoirs,fracturing tracer injection-flowback concentration curve interpretation techniques are used.Because the tracer seepage in the formation will be affected by the morphological parameters of the fracture,such as the length will all reflect the characteristics of the tracer yield concentration curve.Therefore,after analyzing the concentration curve,the fracture parameters after hydraulic fracturing can be obtained,and at the same time,other techniques are used to verify each other and fracture characteristics are described.This paper begins with the study of the principle of fracturing tracer injection-flowback interpretation technology,and studies and analyzes the tracer selection,construction process and process flow using this technology.At the same time,the technological principles'advantages and disadvantages of different fracturing processes used in the construction of several test wells in a tight reservoir were analyzed,and the mechanism of fracture generation under different process conditions was analyzed and compared with the results of micro-seismic event monitoring technology,with corresponding tracer flowback concentration curve characteristics.Conventional volumetric fracturing techniques generate more micro-fractures as the main fracture system,and the corresponding tracer concentration curve is often unimodal.The high conductivity dilatation fracturing technology mostly produces fracture systems dominated by large fractures,and the corresponding tracer concentration curve forms are unimodal or multimodal usually.The fracture system generated by the composite fracturing technique often coexists with micro-fractures and large fractures,and tracer-flowback production concentration curves often have a unimodal parabolic type.Based on the analysis of crack morphology after fracturing,a physical model of fracture formation in different formations after fracturing was established,which was divided into uniform fracture physical model and differential fracture model.In subsequent studies,the model was further evolved into a physical model with uniform fracture zones and a physical model with differential fracture zones.At the same time,the fracture was equivalent to a circular pipe,and the fracture zone was equivalent to a circular pipe bundle composed of multiple round pipes.Combining the convective diffusion mechanism of tracers,based on the tracer flowback mathematical model of unimodal cracks,the establishment of a mathematical model of uniform fracture zones and differential fracture zone tracer backflows,and analysis of different fracture parameters on the curve characteristics impact.The mathematical model was built into function optimization.Using the PSO,the field data of a test well in a tight reservoir was fitted and verified.The fracture physical model and tracer concentration mathematical model established in this paper were verified to practical application and solute problems.