Productivity of hydraulically-fractured horizontal wells in tight oil reservoirs using a linear composite method

摘要

In tight oil reservoirs, horizontal wells log analyses indicate properties of reservoirs, such as permeability and porosity, are unequal along the horizontal wells' direction, those heterogeneity of reservoirs bring huge challenges in productivity predicting and hydraulic fracturing designing. This paper focuses on describing such heterogeneity, analyzes its effects on productivity and optimization of hydraulic fractures' parameters. The heterogeneous reservoir is concluded as a linear composite system, the reservoir is divided into two-zone along horizontal well's direction and each zone' permeability and porosity are different. Then a new rigorous mathematic method to predict the productivity is derived based on volumetric source idealization. The new method is verified through the commercial numerical reservoir simulator (Eclipse). Comparing with cumulative productions of a hydraulically-fractured horizontal well in Xinjiang Oilfield Company, the difference is 95 m(3) for heterogeneous model but raises to 1750 m(3) for homogeneous model, which show heterogeneous model have better predicting ability and two-zone assumption has enough accuracy in application. Parameters study show the difference between the simulated results of homogeneous and heterogeneous model could be 15%, and the degrees will be more serious when length of high permeability zone becomes shorter, reservoir's average permeability becomes lower, or contrast of two zones' permeability becomes bigger. Optimizing hydraulic fractures' parameters can be processed by employing homogeneous model with average permeability, but design more and longer hydraulic fractures in high permeability zone will have significant effect on productivity in early stage, and hydraulic fractures with even space and length would be better for long time production.