Understanding Well Interference and Parent-Child Well Relationships With Liquid Molecular Chemical Tracer Technology

Abstract

In an era where capital markets are hitting the brakes on funding the US shale sector, operators have increasingly pivoted from production growth to maximizing the rates of return via lower-cost wells. One of the major challenges of this new era is the determination of optimal stage and well spacing for a drilling area. For much of the US, the trend has been toward increased job size and rapid downspacing of infill or “child” wells. The unintended consequence of this trend has been an increase in fracture interference and excessive cross-well communication, which results in an overcapitalization of acreage and underperforming child wells as the drainage areas of wells overlap and compete for depleted resources. Within the SCOOP/STACK play, child wells completed in 2017/2018 have been half as productive as their 2015/2016 parent wells, a trend theorized to be directly related to negative fracture interactions. Determining an optimal spacing between parent and infill wells is not a straightforward endeavor. An ideal development strategy is not just about well spacing, as decisions in completion design can exacerbate issues stemming from tight spacing. For this multivariate problem, operators have attempted to use bottomhole pressure measurements to extrapolate fracture interference or to use large data sets in a “trial-and-error” approach to understand well interference behavior. These approaches have significant downsides, relying either on data sets of questionable value or on extrapolating data to and from wells with significantly different geological conditions. One operator in the SCOOP/STACK has attempted to understand well interference with chemical tracer technology. Using liquid molecular tracers, this operator achieved a quantified understanding of flow between parent/child wells with a high degree of confidence. This inexpensive technology has allowed the operator to experiment with well spacing and repressurization of parent wells. This, in turn, permits the rapid evaluation of mitigation techniques to optimize its field development strategy based on an accurate measurement of interwell fluid movement. Tracer Selection Two categories of chemical tracer are commonly used in conjunction with hydraulic fracturing operations: infused solid particulate tracers and liquid molecular tracers. While both tracer products have their strengths and weaknesses, liquid molecular tracers were chosen as a best practice in this study as they allow for quantification of the traced fluid phase, unlike infused solid particulate tracers.