Abstract

Hydraulic fracturing, which has had a long and well established place in petroleum production engineering, especially in the mature areas of North America, has emerged recently with equally large role to play in China. Tight reservoirs including shale gas have promoted Chinese fracturing activities to ever higher levels. Western design and execution techniques have been adopted and modified.

We present field examples for the Shun 9, a low-permeability oil reservoir (permeability ranges from 0.001 to 0.1 md) in North-Western China for which horizontal wells with multiple fractures appear to be the only choice for some credible production. The physical optimization in this work is done with the Unified Fracture Design (UFD), partitioning the well length and employing a large number of fractures. Design of each fracture is treated separately with an allocated drainage area allowing different aspects ratios in each iteration of design.

The UFD approach is augmented by a net present value (NPV) calculation allowing for the critical economic optimization. In past work NPV has been a decisive element in the optimization process, because it utilizes operational costs and hydrocarbon production to evaluate reservoirs which are candidates for exploitation strategies. The number of fractures per well, their spacing and the size of the fractures are the results of this optimization. Actual treatment variables are presented, including all injection variables, fluid and proppant properties.

Based on post-treatment well performance, the entire project presented here is marginal when considering economics e.g., the best is a 5-year NPV of $5 million for a horizontal well with four-transverse fractures. A comprehensive approach is required for this reservoir, optimizing well architecture and costs. What we present in this paper is the procedure to achieve the best physical optimization, followed by the proof of economic viability through the NPV calculation.

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