The increasing trend of drilling infill wells (more than 60% of new wells in 2017) comes with the significant risk of well interference, or "frac hits". Frac hits occur during hydraulic fracturing operations when there is direct pressure communication between the well being treated and adjacent, pre-exisiting wells. In extreme cases, the fracture may fill the adjacent wellbore with sand, which requires expensive cleanup intervention. Fracture geometry control technologies aim to reduce the likelihood of well interference by deploying far-field diversion techniques. This paper presents a unique field experiment that demonstrates the value and effectiveness of these technologies.
In the Bakken, two child wells were drilled 1,300 and 800 ft, respectively, on each side of an existing, partially depleted parent well. Each child well treatment comprised 50 stages of slickwater, completed in zipper frac style. Treatments in the farther well did not utilize any fracture geometry control technology. In the nearer well, 20 of 50 stages (one every 5 stages) included far-field diversion material. All other parameters of the pumping schedules were the same between the two treated wells. Pressures were monitored in all three wells (parent and two child wells) at high frequency during all operations.
The parent well was not damaged during the operation. However, during the first 35 stages of the child well treatments, the parent well's pressure increased in spurts, until it stabilized near expected reservoir pressure. In this paper, each instance of well interference is quantified and attributed to a treatment stage in one of the child wells. Interestingly, not all stages contributed to the pressure buildup. Significantly, various levels of frac hits were observed, as determined by the magnitude and steepness of the pressure increase. The correlation of frac hit with the absence of far-field diverter is striking. The results clearly demonstrate that fracture geometry control technologies reduce the occurrence of direct well interference by containing fracture growth.
The operations in these wells created a unique opportunity to design a field experiment to assess the effect of fracture geometry control technology on well interference during infill well stimulation. The results demonstrate that such technologies reduce the occurrence of direct frac hits in depleted parent wells.