In this paper, we present a mechanistic study for understanding the impact of ‘frac-hits’ on the tight oil ultimate recovery (EUR). ‘Frac-hits’ are defined as the invasion of fracturing fluids into an existing producer (parent well) while a neighboring well (child well) is being fractured. Data from wells that experienced ‘frac-hits’ suggest that substantial amount of fracturing fluids from offset wells may invade the existing producers, indicating high degree of connectivity between the existing producer and the newly stimulated well. Even if the parent well is shutin during the fracturing of the child well, oil rates after re-starting the parent well production were observed to be lower than that prior to shut-in, and the oil production trend line deviates (usually lower) from the original type curve prediction.
We used a mechanistic model to assess the impact of ‘frac-hits’ on oil production. The results indicate that the impact of ‘frac-hits’ on oil production can be significantly different depending on producing pressure of the impacted wells. ‘Frac-hits’ below the bubble point pressures could have long-lasting adverse effects on oil production. Among the mechanisms studied, gas trapping is found to be the most likely mechanism that impacts oil production. Gas trapping occurs when fracturing fluids suddenly invade the depleted matrix due to the relatively large gas compressibility. The snapped-off gas, isolated from the continuous fluid path in the matrix near the fractures, can hinder the oil productivity.
If gas trapping cannot be remediated after ‘frac-hits’, oil EUR may be decreased along with increased water handling. Given this, oil production may be optimized by coordinating the fracturing sequence and spacing to avoid ‘frac-hits’ below the bubble point and avoid re-fracturing in the region below the bubble point.
Over the past decade, technological advances in horizontal drilling and hydraulic fracturing have allowed the access to large volumes of shale oil that were previously uneconomic. The Energy Information Administration (EIA) estimated approximately 419 billion barrels of recoverable shale oil resources in 46 countries (EIA 2016). The United States (US) contributes more than 90 percent of the global shale oil production in 2016. Current production in the US relies heavily on drilling and fracturing large numbers of wells, which is capital intensive.
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