DRAIN HOLE STIMULATION
Vincent, George King, and many other frac experts have found that the major problem with shale wells is constriction zones that form at the intersection of the fracs and the horizontal well (Hwell) and reduce flow rates as shown in Figure 1.
Fig 1 shows the conditions at a “Constriction Zone”
These constriction zones form within 10 feet of the horizontal zone and initially reduce production rates by 20 to 30 percent as shown in Figure 2. The constriction zones form because of the complex frac initiation process at the Hwell.
Eliminating the effects of the constriction zone will therefore increase the initial flow rates 20 to 30 percent.
Ten percent of the proppants in fracs are crushed during the fracing process, producing fine crushed particles that flow into the constriction zones and further plug them as oil and gas are produced as shown in Figure 3.
This additional frac plugging decreases flow rates 50 percent the first year and 70 percent the second year, causing the rapid decline of shale wells.
Frac plugging requires shale wells to be refraced every 2 to 3 years to keep them economical.
Refracing typically stimulates less than 50 percent of the fracs in a well due to difficulties in isolating individual fracs in cemented casing as shown in Figure 4.
Fig 4. MicroSeismic data showing that only fracs near the heel of the well are stimulated
The new stimulation system described below is designed to overcome this problem and stimulate 100 percent of the fracs in all shale wells.
DRAIN HOLE STIMULATION SYSTEM
In 2015, Dr. William Maurer filed a patent on an alternative stimulation system that consists of drilling drain holes that bypass the constriction zones, intersect fracs, and provide large flow paths from the fracs to the Hwells as shown in Figure 5.
What makes these drain holes unique is they are intentionally drilled across hydraulic fractures to increase production rates.
This drain hole is sidetracked from the Hwell using existing sidetracking tools. It will typically be 3 to 4-3/4 inches diameter and 100 to 150 feet long.
This technique uses the same drilling technology used to drill the Hwell so no new drilling tools have to be developed.
The drain holes can be drilled underbalanced to maximize production from these wells.
The drain holes can be drilled across multiple fracs to reduce drilling costs as shown in Figure 6.
Fig. 6 Shows an angled drain hole that intersects multiple fracs
Branched drain holes can be used to intersect fracs at multiple points to increase flow as shown in Figure 7.
Fig 7. Shows a branched drainhole that drills across a frac in multiple places
Horizontal drain holes drilled from the vertical sections of Hwells will stimulate all fracs in a well with a single drain hole as shown in Figure 8.
Figure 8. Shows a horizontal drainhole that intersects and stimulates all of the fracs in a well
The horizontal drain holes can also be drilled from the Hwell as shown in Figure 9.
The horizontal drain holes can be drilled as new wells from the surface in shallower formations as shown by the patent drawing in Figure 10.
Horizontal drain holes will likely be the most popular design since they allow stimulating all fracs in a well with one drainhole.
The above figures show the drain holes drilled in vertical planes. They can also be drilled in horizontal or and any other planes and in 3-D shapes.
The drain holes will be completed open hole or with slotted liners so oil and gas can flow into the drain holes over their entire length whereas with cemented casing there is no inflow along the well.
FRACING DRAIN HOLES
Drain holes completed open hole have the advantage that they can be fraced using straddle packers to create new fracs or stimulate existing fracs as shown in Figure 11. This will increase inflow into the drain holes by intersecting oil and gas filled natural fractures.
Fig. 11 Shows how straddle packers can be use to stimulate old fracs or create new fracs along the drainholes.
PLUGGING DRAIN HOLES
If problems occur with drain holes, they can be plugged with cement to allow conventional refracing to be resumed as shown in Figure 12.
Fig 12. Shows that drainholes can be filled with cement at any time to make them inactive.
BENEFITS OF DRAIN HOLES
- Utilize conventional drilling tools
- Stimulate all fracs in a wall
- Reduce stimulation costs 50 to 60 percent
- Increase flow rates 30 to 70 percent
- Eliminate rapid decline
- Eliminate refracing every 2 to 3 years to keep shale wells economical
FIELD TEST STATUS
This technology was kept confidential until a patent entitled Drain Hole Drilling in a Fractured Reservoir was filed with the US Patent Office on August 27, 2015.
Maurer Engineering is holding discussions with operators about conducting field tests in different shale formations including the Eagle Ford shale which is ideal for this technology.
Read the reports on FRAC PLUGGING and SHALE PROPERTIES because they give considerable insight into oil flow in shale wells mechanisms and allow maximizing oil flow and profits from shale wells.
Persons interested in applying this technology should contact Dr. William Maurer at firstname.lastname@example.org.
READ SPE PAPERS
We recommend that readers get copies of the excellent SPE papers cited in this presentation at www.onepetro.org for more details on these frac plugging mechanisms.