Traditionally, we view well development as the final phase of completion. While development is the final step, successful development starts at the first turn of the bit. How does the drilling program minimize damage to the production zone?
Over the years, I have travelled worldwide to collaborate on hundreds of problematic wells with development issues. Oddly, we call these “development” issues when in reality the problem stems from well completion. Development is a repair solution to the issue. The better approach focuses on how the drilling process blocked the porosity of the production zone in the first place.
Every driller has encountered a well that doesn’t yield as expected. First, we often wonder if maybe we misjudged the production zone. Often that second-guessing comes from our short phase of soil identification, choosing the best available screen and gravel pack. Then we reflect on the moment we hit the production zone. We think about the amount of fluid it took, how quickly it wanted to heave and other nuances competent water well drillers notice. We go into triage mode and create a rigorous development strategy to open the blockage preventing the expected water production we promised our customer.
Undoing the damage caused during the drilling phase will always be the final step in producing water. We, as drillers, need to gauge the level of necessary disruption and think about how much time it takes to repair that disruption. Minimizing the disturbance is not impossible. It does take reflection on past mistakes to gain a better understanding of the significant impacts that can harm a productive, water-bearing formation.
Many drillers run into a common well production issue after implementing new equipment — often after purchase of a new rig. I get calls from drillers describing the company’s investment into a new rig, only to have issues creating the same productive wells as before. They question whether performance has a psychological component, as if the old rig were a lucky charm like that old baseball glove from an undefeated season. Yes, a new rig requires a learning phase, but it’s much more technical than that. It takes time, with new equipment, to pick up the same signs that the old rig gave — the signs we use to guide us to the best well possible.
When the focus turns to the motivation for buying a newer rig, I often hear one simple answer: to have the ability to drill faster, smarter, safer and, sometimes, deeper. A rig with those capabilities must have higher rotation speeds, more pulldown and higher top-head travel speed. Increasing those capabilities increases the potential for disruption. Remember Spider-Man’s mantra: “With great power comes great responsibility.” Faster rotation creates smaller solids. When combined with more pulldown or travel speed, we force those fine solids out into porous formations.
Once we understand that great power causes the majority of well development problems, we can focus on preventing that damage. First, go back to basics. Starts by creating and maintaining cutting sizes that range between 1-1½ inches. Tricone bits make maintaining that size easy. However, in delicate formations, keeping to that size proves impossible. Then, make it the goal to remove the largest possible unpulverized solids. If these solids deteriorate and recirculate downhole, the greater power of that new rig can start cementing off the porosity zone.
That scenario involves a basic tricone. Consider a PDC bit. It operates at higher rotation with cutter heads that create finer cuttings while increasing penetration rates in hard, competent formations. Again, with great production power, our drilling program can entrain and recirculate finer solids, having an impact on the porosity zone. A proper drilling and solids control program can prevent 90% of formation blinding. Again, go back to basics: Drill with a fluid under 5% solids or less than 9 pounds per gallon.
Once a driller understands the damage the drilling phase can cause and the impacts of diminished development energy, they can maximize their well development strategy.
An impactful well-development program requires focused energy to repair the blinded porosity zones. Ironically, as our rigs increase in power and allow for faster well completion that same power can diminish the energy necessary for well development. The most significant way this energy dissipates is through increased borehole diameter. Sometimes we choose a larger-diameter borehole in the design phase because the bigger rig has the capabilities. Other times, a poor drilling program causes an eroded, out-of-gauge borehole. Either situation leads to a thicker gravel pack. However, that thickness diminishes the energy trying to repair any blinding. Any development method or fluids has to travel further from the screen to the production zone. The combination of a thicker gravel pack and a thicker filter cake can absorb 50% to 70% of that focused energy.
Once a driller understands the damage the drilling phase can cause and the impacts of diminished development energy, they can maximize their well development strategy. Air development, the simplest method, proves most effective when the drilling program has prevented significant damage to the formation. Air development is most effective from 1-3 inches outside the screened interval. Yes, higher CFMs equal greater disruption downhole and more water moved, but that great power can collapse the production zone again.
For a plugged, blinded-off formation, go with focused energy for a high-impact development solution. High-velocity jetting excels at breaking down filter cake and opening blinded pathways. The goal is to isolate jetting to less than 3 feet of the screened interval at a time. This focused jetting can utilize air or a development fluid, but I prefer a phosphate-free dispersant fluid mixed up at two times the screened volume. I jet that fluid into the 3-foot section while calculating fluid volume pumped in along with time.
After jetting the screen from top to bottom and then bottom to top, I switch to swabbing the formation. As a rule of thumb, I use a minimum of three minutes per foot of the screen. Finally, I utilize an airlift to evaluate the material removed from the formation. If the damage is significant, the preferred method is a dual-disc swab using a reverse circulation airlift. The best well-development strategy implements multiple energy methods and agitation to repair the disruption caused during the drilling and construction phase.Well development has changed significantly in the past 30 years as the industry shifted from walking beams and surge blocks to the outlawing of phosphates-based development fluids. We lost a lot of good development energy by losing walking beams on rigs. We gained better practices by eliminating phosphate nutrient sources for bacteria. Remember, the best method for creating a productive water well is to minimize our impact. Drilling will always be disruptive. It’s up to us to understanding how we focus power and energy to undo that disruption.