In this study, we present a method to monitor inter-well communication and drainage frac height through time based on unique geochemical fingerprint data collected from oils. This method does not require expensive instruments or interfere with production and its results were integrated with independent pressure gauge and well performance data to enable data-driven decisions on well spacing, well stacking and completion designs with different subsurface configurations.

Produced oils of 9 horizontal wells over ~20 months and cuttings samples from the vertical section of an adjacent well were collected in the study area located in Midland Basin, Texas. The 9 producing wells were in two DSUs with two different well configurations, one drilled with two landing targets while the other with three. Thousands of chemical compounds that are naturally occurring in the produced oils and oils extracted from the cuttings, were profiled and interpreted geochemically. Drainage frac heights and quantitative production allocation by zone were conducted by building a geochemistry-based model correlating the produced oils back to their contributing intervals represented by the cuttings samples and their vertical depths. The probability of inter-well fluid communication between each of the well pairs was calculated based on the similarity of the geochemical fingerprints in the produced oils of the corresponding wells.

Our data showed that the three targets scenario generated significantly more overlapped drainage vertically and vertical well communication than the two targets scenario. Up to ~60% of the drainage frac height of the Middle well in the three targets scenario overlapped with the Upper wells and ~20% overlapped with the Lower wells, while in the two targets scenario the Upper and Lower wells only showed ~40% overlapped vertical drainage. The lateral geochemical similarity index (SIL) calculation showed correlation between higher SIL (stronger lateral well communication) and poorer oil production rates, indicating well communication could impair well performance. The data also showed significant variation of lateral communication through time which was strongest about a month into production and then reduced through time. Even with the same spacing and completion design, the Upper wells showed higher SIL (i.e., more communication) than the Lower wells, indicating geology and completion design parameters such as sand and fluid volume, and clusters should be taken into consideration for future planning. Independent pressure data also supported these observations, providing critical evidence for optimizing the stacking, spacing, and completion designs of future development wells.

Geochemical data in the produced oils carry significant information to reveal subsurface fluid flow and well interaction through time. It provides actionable data to support various field development decisions such as well spacing, well stacking, landing target optimization, well sequencing, and completion designs.

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