Multi-stage Fracturing Horizontal Well Productivity Evaluation In Tight Reservoirs

Tight oil is a new hot spot after shale gas in the exploration and development of global unconventional oil and gas. Generally horizontal well combined with multistage fracturing technology is used for mining this kind of reservoir. So how to accurately evaluate the productivity of multistage fractured horizontal wells is of great significance to the exploitation of tight oil reservoirs.Based on in-depth analysis of the characteristics and percolation mechanism of tight reservoir, this paper establishes mathematical productivity model of horizontal well in tight oil reservoir by applying conservation law of mass, seepage mechanics and numerical simulation. Next, the mathematical model is discretized by using the finite difference method, and numerical calculation model of the multistage fracturing horizontal well is obtained after linearization. Then the production characteristic and the production decline rule of the fractured horizontal well in tight reservoir are obtained by programming calculation and the influencing factors are analyzed. At last, the model is verified and applied by the case analysis, and the following points are obtained:(1) Tight oil reservoir is characterized by dense lithology and poor physical property. Due to the low maturity of sediments, fine particles, poor sorting, high content of cement and strong diagenesis, the porosity of tight oil reservoir is low and of great variation, and the pore structure is complex, which distinguishes the migration mechanism of this reservoir from that of conventional reservoirs.(2) On the basis of the characteristics of tight reservoir, in this paper, a flowing mathematical model of tight oil reservoir considering start-up pressure gradient is established applying the conservation law of mass. The numerical model of fracturing horizontal well productivity in tight oil reservoir is obtained by using PEBI grid. Based on the productivity numerical model and material balance theory, the mathematical model of Blasingame production decline is established. Through using mirror image and superposition principle, a mathematical model for the prediction of the contribution of liquid production rate is established.(3) Based on the results of numerical simulation of multistage fracturing horizontal well in tight oil reservoir, the oil well flow phases are divided according to flow process. We analyzed the effect of fracturing series, fracture half length, spacing and the starting pressure gradient parameters on the productivity decline curve of multi-stage fractured horizontal well in tight reservoir.(4) The production and decline rate of a multistage fracturing horizontal well in a tight oil reservoir in Daqing are predicted for by Blasingame analysis. Meanwhile, we estimate relevant parameters such as permeability, reservoir pressure and dynamic reserve of tight reservoir and predict the degree of contribution of different cracks.The research results of this paper provide important guiding significance for the dynamic analysis and productivity evaluation of tight reservoir.