Abstract

The creation of a productive stimulated reservoir volume (SRV) is of paramount importance in ultra-tight reservoir rock. In an infill drilling scenario, fluid injected during hydraulic fracturing operations will tend to find pre-existing depleted fracture networks and simply restimulate existing SRV, resulting in a significant reduction in the capital efficiency of completion dollars. Furthermore, infill fracturing operations often damage the parent wells, temporarily (and sometimes permanently) reducing their productive capabilities. There are a number of cases in the Eagle Ford where infill drilling has led directly to a net loss of expected ultimate recovery for the drilling spacing unit (DSU). This case study highlights how a pinpoint (single entry point per stage) completion in the Eagle Ford was able to achieve a large productive SRV, accessing previously unstimulated rock; despite being bounded at 700 feet on either side by existing producers.

Three wells are analyzed: two original plug-and-perf wells plus the subject infill well. Rate Transient Analysis (RTA) and reservoir simulation are the primary analysis tools for this case study. Analysis techniques include Flowing Material Balance to interpret productive SRV and specialized plots to evaluate total fracture area and apparent completion skin. Analytical models are used to validate the interpretation and numerical models are used to forecast future production.

The infill well was able to achieve an SRV and consequent productivity commensurate to the treatment size and stage density, apparently without suffering any inefficiencies that would normally result from reactivating depleted SRV. It also exhibits a significant damage skin which acts like a downhole choke, limiting the expected high flush production rate and flowing pressure. However, this skin may have also inhibited the stress induced productivity loss common in the Eagle Ford, thereby leading to lower than expected decline rates. Producing well interference is observed, and is believed to be a result of subsurface connectivity through the fracture networks combined with a substantial flowing pressure gradient between the infill and its offsets.

Based on our experience in the Eagle Ford, the following observations from this case study are unusual, and have led to some novel insights-

  • Producing well interference at 700 ft well spacing within 3 months from the start of production

  • An infill well achieving a larger than expected SRV

  • High apparent completion skin damage (or low apparent fracture conductivity). Usually Eagle Ford completions result in very low (or zero) apparent skin

  • Parent wells have endured multiple frac hits from offsets prior to the infill well coming on-stream. Productivity loss resulting from the infill frac hit appears to be restored within only a few months, although production lost due to the damage from earlier frac hits may not be restored

The results from this work may have major implications regarding future completion design and field development planning decisions.

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