The effect of horizontal well spacing on stimulation performance and well results is of keen scientific and economic interest to the industry. The objective of this paper is to demonstrate these effects in a grouping of five horizontal Wolfcamp wells drilled in a down-spaced configuration where inter-well distances were reduced from 1320′ to 660′.

The subject project is located in Ward County, Texas, on a 640 acre lease. A stand-alone Wolfcamp A2 zone well (legacy well) was drilled on the project acreage in late 2016 followed by the drilling of four development wells directly offsetting the legacy well in mid-2018. The four development wells were spaced 660′ apart as opposed to the existing norm of 1320′. This paper presents various pressure, microseismic, tracer, and production data collected during and following the zipper stimulation of the four development wells. This rich data set yielded significant information about the drainage characteristics of the legacy well, the effect of pressure depletion on fracture geometry, the nature of fracture driven interactions (FDI) in down-spaced wells, and the inter-relationship of these factors in their effect on production results. Active well defense was performed in the legacy well and results from these defense operations is also reported.

Inter-well spacing of 660′ between wells in the same zone resulted in significantly diminished production results compared to the base case resulting in lowered projected rates of return for the well group. Depletion in the legacy well resulted in larger fracture geometries in the nearest development wells, but not in wells 990′ away. This resulted in larger stimulated volumes in the nearer wells but also diminished oil production. The inferential conclusion is that localizing stimulation energy in the near vicinity of the treated well yields improved well results. Concerning FDI, the data indicate that wells within 660′ of each other are likely to interfere with each other, while the opposite was true for wells that were 990′ apart.

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