Multi-Stage Fracturing Seepage Model and Productivity Prediction Method for Horizontal Wells in Shale Oil Reservoir-Use Horizontal Wells in Qingcheng Oil Field, China, as an Example

Abstract

Shale oil in Ordos basin, China, is being developed using horizontal well and volume fracturing. Elastic energy, dissolved gas expansion etc. are the main driving forces for fluid flowing from matrix to horizontal wellbore. However, flow mechanism varies greatly when hydrocarbon flows from matrix to artificial fractures and then to wellbore, due to huge differences in the sizes of flow channel, from nano-scale pore-throat in matrix to meter-scale channel in wellbore. Thus, a reasonable mathematical description of the structural characteristics of complex fracture networks is important for an accurate productivity prediction model of a horizontal well. In this paper, a physical model was first built dividing fluid seepage area into three sections and five small zones, which are horizontal wellbore zone, highly transformed zone, weakly transformed zone, drainage zone in matrix and the non-drainage zone in matrix. Joukowski transformation was then introduced before a mathematical solution was deduced, where law of equivalent seepage resistance and material balance method were applied. Then mathematical model of seepage in five different zones were built based on the solution considering different flow patterns, threshold pressure gradient and stress sensitivity in those zones. Productivity equation of multi-section-coupled seepage flow in three sections was deduced afterwards and came up with a fast calculation method to predict productivity in horizontal well with multi-scale nonlinear characteristics by solving analytical solutions for multistage mathematical models. The method has been applied to simulate dynamic development performance in 67 horizontal wells (have been producing for over 3 years) in Qingcheng oil field, Ordos basin, China, with an 82.01% of accuracy. The developed simulation model is expected to be applicable not only in the prediction of development performance in horizontal wells in shale oil and gas reservoir but also in other unconventional reservoirs such as carbonate reservoirs. The process may shed light on the ways to increase the total productivity of oil and gas recovery in hydrocarbon industry.