Effect of Completion Heterogeneity in a Horizontal Well With Multiple Fractures on the Long-Term Forecast in Shale-Gas Reservoirs

Abstract

Shale gas reservoirs have become a significant source of gas supply in North America because of the advancement of drilling and stimulation techniques enabling commercial development. The most popular method for exploiting shale gas reservoirs today is the use of long horizontal wells completed with multiple-fracturing stages [multifractured horizontal wells (MFHW)]. The stimulation process may result in biwing fractures or a complex hydraulic-fracture network. However, there is no method to differentiate between these two scenarios with production data analysis alone, making accurate forecasting difficult. For simplicity, hydraulic fractures are often considered biwing when analyzing production data. A conceptual model that is often used for analyzing MFHWs is that of a homogeneous completion in which all fractures have the same length. However, fractures of equal length are rarely if ever observed (Ambrose et al. 2011). In this paper, production data from heterogeneous MFHWs (i.e., where all fracture lengths are not the same) is studied for reservoirs with extremely low permeability. First, the simplified forecasting method of Nobakht et al. (2012), developed for homogeneous completions, is extended to heterogeneous completions. For one specific case, the Arps' decline exponent is correlated to the heterogeneity of the completion. It is found that, as expected, Arps' decline exponent (used after the end of linear flow) increases with the heterogeneity of the completion. Finally, it is shown that ignoring the heterogeneity of the completion can have a material effect on the long-term forecast. We have assumed planar hydraulic-fracture geometries for our modelling in this work and discuss the implications of this when more-complex fracture geometries are created. This seems to be more common in shale gas reservoirs. We provide an example of low-complexity, planar fracture geometries created near an MFHW and observed on an image log at an offset well.