Abstract

Multi-stage hydraulic fracturing has become the key technology to complete horizontal wells in shale gas reservoirs. In each stage, multiple perforation clusters are used to create multiple transverse fractures. How to place these clusters significantly affects both the short-term and long-term production performance of horizontal shale gas wells. The author’s previous work has demonstrated that when more than two fractures are created, mechanical interaction among fractures creates strong stress concentrations around the inner fractures. As a result, the fractures between two edge fractures, i.e., sub-center and center fractures, are limited to dilate, and their widths are much less than the edge-fractures’ width.

In this paper, reservoir simulation models were constructed by quantitatively incorporating the findings of the author’s previous work to investigate the impacts of the number of perforation clusters and cluster spacing on production performance of horizontal shale gas wells. The paper illustrates that with the same cluster spacing, the scenario with more clusters has lower ultimate gas recovery because of increased number of less-effective inner fractures. Given the same lateral length of a horizontal well, although reducing cluster spacing increases the total number of fractures, smaller cluster spacing doesn’t necessarily improve well performance. An inadequate small cluster spacing can actually lead to more less-effective and ineffective fractures, and therefore lower gas rate and ultimate recovery.

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