The oil industry is changing at a rapid pace and, “traditional,” methods of stimulation of production and/or injection wells are not always cost-effective. The new paradigm in the industry now calls for progressive, logical thought and careful implementation of procedures. The old ways of doing things “because that’s how we have always done it” may no longer be a viable option as new tools and systems are developed.

Before treatment, a Peruvian water well was clogged with calcium scale. (Photos courtesy of Downhole Fluidics Inc.)

One such tool system, first introduced in 1992, is known as a “True Fluidic Oscillator” (TFO) and “PerfClean International Tool Systems” (PCT). The PCT has been proven successful in more than 6,000 stimulation treatments working in 30 states, 39 foreign countries and most major offshore locations globally. Treatments have been successfully performed in wells from 90 to 27,000 ft (27 to 3,235 m) deep with diameters as large as 36 in. and temperatures above 750°F (398°C). This system was developed and patented by PerfClean International, Inc., predecessor to Downhole Fluidics, Inc., of Midland, Texas, which currently holds four patents on the technology. The company and its licensees perform treatments that are designed to remove near wellbore damage and restore or increase the porosity and permeability of the near wellbore area in all types of wells. Treatments range from primary stimulation of the formation to remedial workovers in new, old, production, injection and disposal wells, vertical, horizontal, cased hole, open hole, screens, slotted liners, etc., in oil, gas, gas storage, geothermal and water wells. The systems are comprised of a primary oscillator in two sizes, 1.5-in. outside diameter and 1.25-in. outside diameter, along with ancillary tools and may be used in conjunction with a coiled tubing unit or on conventional production tubing, drill pipe, wash pipe, etc., when there is a rig present on the well.


To better understand how the system works it is necessary to become familiar with a few terms:


Fluidic — of, relating to, or being a device such as an amplifier or control that depends for operation on the pressures and flows of a fluid in precisely shaped channels. This means there are no moving parts in the PCT.

Following treatment to get rid of wellbore and near-wellbore damage, the well flowed again.

Problems encountered using mechanical devices to create fluctuation of the fluid, such as a ball and race, a flapper, or plunger, etc., as the mechanism dissipates a substantial amount of the potential energy needed to accomplish the desired results. Having no moving parts in a TFO is critical to harness and effectively use as much of the available potential energy as is possible.


Acoustic Streaming — the production of unidirectional flow currents in a fluid produced by the presence of sound waves. The PCT is also a sonic tool which allows pinpoint placement of the fluid being pumped.


Synergism — the interaction of the combined effect of the elements is greater than the sum of their individual effects. A combination of the pressure pulse, acoustic streaming, and chemical reaction of the fluid for the treatment.


The TFO creates pulsating pressure waves within the well bore and formation fluids. Upon contact these pressure waves break up any type of near wellbore damage or blockage which may be caused by perforation damage, scales of all types, fines, emulsions, lost or dehydrated drilling mud or hardened paraffin or asphaltenes, etc.

The True Fluidic Oscillator breaks up obstructions with no moving parts.


One major obstacle to overcome in production/injection wells is scale. Scale is normally built up in layers, either different layers of sizes and types of scale, or layers of scale and paraffin, scale crystals, etc., and may be embedded into the matrix of the formation, and is seldom if ever completely homogeneous. Because different materials vibrate at different frequencies, when the compression waves created by the PCT hit the various materials, the waves cause the material to vibrate. Because there are dissimilar materials within that body of scale or skin damage, there are different rates of vibration which causes the material to reach its fatigue failure point, fall apart and disintegrate.


When treating scales such as barium and/or strontium, which aren’t acid soluble, the fluid of choice is water. In many instances service companies have attempted to remove these types of scale, without success, using standard methods. After educated consideration the PCT has been used and thus far, proven successful.


Examples


Gulf of Mexico


Problem: Decline in production.


Solution: The PCT was run into this well on coiled tubing, in conjunction with a CO2 acid stimulation job.


Results: Prior to the PCT treatment the well produced 1,100 b/d of oil on a 22/64-in. choke and afterward produced 2,100 b/d of oil on a 28/64-in. choke.


Bogota, Texas


Problem: Injectivity decline and pressure increase.


Solution: The 1.25-in. PCT tool was run into this well on a 1.25-in. coiled tubing.


Results: The perforations were cleaned with straight water. The well then went from an injectivity of 48 b/d at 1500 psi to 360 b/d. Next, 1,600 gal. of 15% HCl and 800 gal. of xylene were pumped into the formation. The injection rate then increased to 475 b/d at 500 psi. The goal was 400 b/d at less than 2,000 psi.


J.W. Operating, Barnett Shale, North Texas


Problem: This operator has an ongoing drilling and redevelopment program in the Barnett Shale play. Research of records for the previous year showed the majority of wells exhibited a near-wellbore friction pressure of 400 to 1,000 psi at the target frac rate of 50 to 60 bbl/minute. This high friction pressure was a detriment to the frac program, and a possible solution to the problem was sought.


Solution: The standard PCT tool with the 1.5-in. oscillator was used to clean the perforations and near wellbore area on six wells. Each well was treated by reciprocating the PCT tool across the interval while pumping water with 2% KCl as the treating fluid at a rate of 1.25 b/minute to 2.5 b/minute.


Results: Significant amounts of barium, calcium and iron sulfide scales were recovered during the treatment of these wells.


Well #1 — during the follow-up frac treatment the near wellbore friction pressure was determined to be <50 psi.


Well #2 — during follow-up frac treatment near wellbore friction pressure was determined to be 200 to 250psi.


Well #3 — during the follow-up frac treatment near wellbore friction pressure was determined to be 108 psi.


Well #4 — after an attempt to frac this well was terminated due to near wellbore friction pressure of 1,081 psi while pumping the pad, the PCT tool was run as in previous wells. The second attempt to frac was successful with the near wellbore friction pressure of 204 psi.


Well #5 — after an attempt to frac this well was terminated due to near wellbore friction pressure of 1,700 to 1,900 psi while pumping the pad, the PCT tool was run as in previous wells. The second attempt to frac was successful with near wellbore friction pressure of 25 psi.


Well #6 — although significant amounts of barium and iron sulfide were also recovered from this well, the well was not fractured due to communication with the Ellenberger formation.


Cooper Basin, Australia


Problem: Production completely ceased due to buildup of barium scale.


Solution: A 1.50-in. PCT tool provided near-wellbore stimulation to remove barium scale deposits from 8,035 ft to 9,313 ft (2,451 to 2,840 m), The first run, involved running a mud motor with the PCT tool installed inside a StimMill to remove scale from 8,035 ft to 8,066 ft (2,451 to 2,460 m). The well began flowing with 450 psi. The final run was with only the PCT tool to perform a stimulation treatment across the seven perforated intervals located from 8,068 to 9,283 ft (2,461 to 2,831 m). Nitrogen was pumped to dewater the well and bring it on production while pull out of hole. Afterwards, the flowing wellhead


pressure was between 800 and 1000 psi. and reportedly flowing at 3.1MMcf/d of gas.


These few examples illustrate the versatility of the system in stimulation and remediation of production/injection wells. For additional information, see www.dhfluidics.com and please review these SPE Papers; Cal/Tex-Sumatra SPE-86545, Chevron/Texaco-N. Sea SPE-81732, Bapteco-Egypt SPE-93987, Kinder Morgan-Oklahoma SPE-93910, PDO/Oman SPE-89653.