Measurement and Analysis of 3D Stress Shadowing Related to the Spacing of Hydraulic Fracturing in Unconventional Reservoirs

Abstract

Abstract Industry experience in unconventional plays shows that production performance does not scale up in simple increments when adding hydraulic fracture stages in closely spaced completions. That is, adding stages to a planned well by reducing the stage spacing does not proportionally enable additional hydrocarbon production on a per stage basis. Instead, closer stage spacing incrementally adds less hydrocarbon production per stage. Determining the appropriate stage spacing is an optimization step that the industry has approached by drilling statistically significant numbers of wells to separate the effects of completions from the effects of geologic variations. We propose leveraging and integrating microseismic data with associated measurements to analyze and model the effects of reduced stage spacing while drilling fewer wells. Hess Corporation is using downhole geophones to monitor microseismic events associated with hydraulic fracturing in horizontal wells with different completion stage spacings in the Middle Bakken Play and the Utica Play. By constructing a small 3D structural model around each well, we create depth histograms of microseismic events. The events are measured in relation to a common stratigraphic boundary in order to identify how hydraulic fractures interact. Stage to stage analysis of these histograms shows a systematic interference phenomenon, which we demonstrate by applying 2D Fast Fourier Transform, correlation, and quantile analysis to the histograms. A comparison of three horizontal wells stimulated with different stage spacing and in different plays shows that hydraulic fractures in closely spaced stages interfere with each other by cyclically bouncing out-of-zone. We find from microseismic observation that the stress shadowing induced by closely spaced stages exhibits a 3D behavior. That is, when hydraulic fractures develop in-zone, as planned, stress accumulates and forces subsequent completions preferentially upward, out-of-zone. As stress accumulates in the zone above, the following fractures reform and are back in-zone in a repetitive cycle. We believe that the physics controlling incremental hydrocarbon production per stage is related to this observed cyclical reduction of the in-zone fracture area. We then analyze the changes to in-situ stress induced by closely-spaced hydraulic fracturing, using a simple model. The concept uses geomechanical principles to explain the in-zone and out-of-zone phenomenon observed in multi-stage fracturing. In the future, we plan to apply 3D stress shadowing theory to our completion models to optimize the stage spacing of our production wells.