Investigation of the Economic Impact of Parent Well Protection Treatments in Unconventional Plays
Authors: Dhuldhoya Karan , Dusterhoft Ron 
Published: March 2017

Abstract
Because commodity prices have substantially decreased since peaking in late 2014, operators have implemented strategies that focus on the most prolific acreage and have concentrated drilling activities on the "sweet spots" in many unconventional plays. This development practice has resulted in decreased well spacing and infill (development) wells being drilled in close proximity to parent (delineation) wells, causing lower productivity than expected in many development wells because of drainage area and fracture interference. Many operators use a method known as parent well protection (PWP) to help mitigate this effect and increase recovery from both parent (delineation) and closely offsetting development (child) wells. This paper presents an analysis of the economic impact of PWP treatments performed for repressurizing the reservoir system and chemical stimulation of the parent well.
This evaluation of PWP production benefits was performed using a combination of numerical reservoir simulation with advanced gridding and reservoir modeling capabilities and economic analysis tools for net present value (NPV) evaluation. Advanced modeling capabilities helped enable grid transformation of the simulation grid at the time of completion of the infill well to simulate the effects of drainage area interference. Wellbore flow parameter alterations modeling near-wellbore (NWB) and skin damage effects were implemented. In addition to fracture interference mitigation, NWB damage remediation of the parent well was implemented at varying magnitudes to simulate the effects of a chemical stimulation treatment performed in conjunction with the repressurization treatment. An analysis of the fiscal impact of the PWP treatment with water only and PWP treatment with stimulation fluids was performed to determine the scenario with optimal NPV.
Results indicated that substantial benefit can be realized through PWP treatments. The primary goal of the PWP treatment is to help prevent production loss in the parent well and mitigate production interference from the child well completion. Production interference is caused by asymmetric fracture growth from the child well completions into the depleted region around the parent well (typically the area of least stress). Simulation results showed that mitigation of asymmetric fracture growth can result in an increase in 4-year cumulative recovery of up to 21%. Chemical stimulation treatments addressing only NWB/skin damage can result in an increase in 4-year cumulative recovery of up to 16%. Combining both resulted in an increase of up to 36%. The break-even price for the cost of the PWP treatment, rate of return (ROR), and return on investment (ROI) were evaluated and associated with the cumulative production of the various reservoir models. This paper presents case histories and examples of PWP treatments.
The benefits of PWP treatments cannot only be evaluated based on the incremental recovery in the parent well, but should also take into account production loss from fracture interference in both the parent and child wells. Increased recovery and economics can be achieved through stimulation of the parent well in conjunction with repressurizing, prior to completion of the child well.