[Editor's note: This article originally appeared in the November issue of E&P Plus. Subscribe to the digital publication here.]  

Propellant-boosted perforating has proven to affordably increase completion and recompletion performance in a wide variety of saltwater disposal (SWD) wells and producers. Advances in integrating propellants with traditional shaped-charge perforating technology have enabled perforating and stimulation operations to be performed in one trip at lower cost than traditional two-step, shoot-and-treat methods. The critical success factor is the adoption of a progressively burning, solid propellant designed to increase penetration, eliminate clogged perforations and overcome near-wellbore damage from compaction caused by traditional shaped-charge perforators.

Boosting SWD injectivity

E&P companies invest millions of dollars to safely dispose of produced water in wells they own and operate or in third-party, off-lease wells. With SWD costs in some areas reaching half of a well’s operating costs, operators in the Permian, Illinois and other basins are adopting the propellant-enhanced perforating technique to improve injectivity index and lower operating expenses.

Standard perforating gun systems enhanced with propellant boosters create multiple 10-ft or longer radial fractures that remove skin to enhance the injectivity index. After the shaped charge fires and penetrates the casing, the slower progressively burning propellant breaks down the formation to lower treating pressures, reduce acid volume and improve rates.

For a Delaware Basin operator, Enhanced Energetics applied propellant-boosted perforating technology during the initial completion of an SWD well. Step tests proved propellant boosters improved perf injection efficiency when compared to traditional perforating, and the volume of acid required for stimulation was reduced. The step test achieved an injection rate of 28 bbl/min at 1,866 psi. This result indicated the SWD well had about 35,000 bbl of daily capacity at a permitted pressure of 1,500 psi.

Compared to offset wells, this 71% increase in injection volume was achieved at the same pressure. Compared to status quo offset SWD well completions, the propellant-enhanced SWD required 50% less acid, rig time decreased by an average of five days, and the lower pressure needed to achieve permitted rates reduced the horizontal pump size and associated power consumption.

Boosting conventional and unconventional production

Enhancing perforations in conventional and unconventional wells with propellant boosters has delivered step changes in completion performance. In vertical and horizontal wells, propellant boosters with shaped charges extend the technical limit of conventional perforating performance by breaking down every perforation tunnel in advance of treatment operations. Fractures created in perforation tunnels bypass skin to enhance productivity and lower treating pressures. More than 6,000 wells have been completed with propellants worldwide in carbonates, sandstones and naturally fractured reservoirs.

Step-rate tests

Step-rate tests in a new well completion (top) with propellant-boosted perforating versus an offset well (bottom) with traditional perforating prove propellants drive higher injection volume. (Source: Enhanced Energetics)

In 2019 an operator in the San Andres dolomite formation in the Permian Basin recompleted two wells initially completed with conventional perforations and acid treatment. The propellant-boosted perforating gun overcame formation damage and improved the performance of the subsequent acid stimulation. A 5,000-gal acid job was run after each Kraken perforating job. For several months, one well doubled production and the second well more than tripled production with the propellant-boosted stimulation method.

Recent work in unconventional wells with plug-and-perf completions showed promising results that have not yet been released by operators. Large datasets are being analyzed to compare results with and without propellant-boosted perforating. The metrics impacted include higher pumping rate, minimizing time to achieve rate and complete each stage, lowering the chance of screenouts, and increasing prop volume.

Tests confirm effectiveness

An API Recommended Practices 19B, Section 4 Test at Halliburton’s Jet Research Center evaluated perforation flow performance with conventional and propellant-boosted perforating guns.

The difference in flow performance between a perforation with no propellant boosters and a perforation with boosters was dramatic. The propellant-boosted enhanced perforation achieved more than 2.5 times the flow rate through the core test sample with a 50% reduction in pressure compared to the shaped charge alone.

In the two perforating tests with a shaped charge assisted by propellant boosters, propellant ignition occurred immediately after the explosion of the shaped charge. The burning of the propellant boosters generated high-pressure gas inside the gun and exited out into the perforation tunnel. This process creates a dynamic-overbalance event that enhances the perforation and creates fractures past the compacted rock (skin) produced by conventional shaped charges, thereby improving access to the formation.

Overcoming inertia to adopt propellants

Operators and wireline service companies that study actual well performance results and API test data are viewing propellant boosters as a standard completion method to reduce risk and lower the total cost of operations.

When completion engineers consider the following four factors they become more willing to adopt propellants:

  1. Propellant boosters are safe to handle and transport;
  2. They are compatible with deep-penetrating, big-hole and equal-hole entry charges;
  3. Tools are assembled and verified away from the well site to lower operations risk; and
  4. Gun systems enhanced with propellant boosters can be conveyed and fired by all standard methods and with customized shot densities and phasings.