This case study involves three infill (i.e., "child") wells drilled near a producing primary (i.e., "parent") well. All study wells target the same unconventional sandstone formation. The project objective is quantifying the interactions between the primary and infill wells. Such understanding will guide future development.
The operator drilled five infill wells west of the primary well, two infill wells were drilled shallower than the three study wells. The primary well produced for seven months before the infill wells’ completions. Of the three study wells, Well 3 is closest to the primary well. To mitigate interference from the infill wells, the operator 1) shut in the primary well during infill stimulation and 2) fractured the infill wells in an east-to-west "zipper" order, starting with Well 3. To monitor communication among the wells, the operator placed a bottom hole pressure gauge in the primary well and pumped fluid tracers in Wells 2 and 3. For an understanding of fracture geometry, the operator monitored the infill well stimulations with microseismic, which measures the acoustic response of fracturing, and electromagnetic (EM) fluid tracking. EM fluid tracking uses Controlled Source Electromagnetics (CSEM) technology to measure the changes in subsurface resistivity caused by treatment fluid injection. Injecting fracturing fluid into the source rock alters a generated EM field causing measurable differences on the surface. As a result, the technique maps fluid movement over time. These results highlight when treatment fluid preferentially develops toward the primary well.
After drilling a primary well, deciding how to optimally develop the remainder of any given acreage can be a daunting challenge. Supported by theory and experience, each technical individual in a multi-disciplinary team has their own operational "secret sauce" to achieve the best results. As fields mature, operators developing unconventional basins drill a higher percentage of infill wells than primary wells and most of those wells are simply not as productive as the primary (Schaefer, 2019). Understanding what factors drive well performance is critical for operators to succeed in the current low-price environment. Testing different completion designs through a trail-and-error method and waiting for production results is neither efficient nor likely to yield conclusive results. Thus, operators must gather data during completions to measure fracture development and qualify design effectiveness. Without corroborating measurements, pressure gauges alone do not provide a complete picture of what occurs downhole during completions.