In an effort to demonstrate the importance of chemistry in directional drilling mud recycling systems, Kem-Tron Technologies recently completed a field trial that demonstrated the benefits of chemically-enhanced mechanical separation. This case study highlights a hybrid drilling fluid that exhibited formation-appropriate drilling properties, while providing ultra-fine solids removal from the drilling fluid.
This hybrid drilling fluid ultimately led to an improved rate of penetration and a 100 percent closed-loop waste management system; therefore saving time, money and the environment.
Kem-Tron’s field trial partner, Parker Lane Directional Drilling has been working throughout the Barnett Shale
Region. This region is plagued with montmorillonite clay and mudstone. The montmorillonite clays and mudstone are highly dispersive in water (“reactive”), causing a host of drilling-related problems. As was further confirmed by a Particle Size Distribution (PSD) Analysis conducted at the site, 85 percent of all solids shown were less than 10 microns and 100 percent were less than 50 microns. Given the nature of conventional drilling fluid reclamation systems, the best cut point that can be practically achieved would be 20 microns. Given Parker Lane’s situation, this is just 15 percent of all solids present.
Specific to the jobsite, a 330×500 rig drilled a 26-in. diameter borehole 4,700 ft. Additionally, there were three shorter bores completed using a 100×120 drilling rig; the first was a 1,600-ft, 24-in. borehole, the second was a 250-ft, 24-in. borehole and the third was a 250-ft, 20-in. borehole.
Conventional mud recycling systems allow silt-size particles to be re-circulated and ground up into ultra-fine/colloidal size particles that can only be removed by hauling off-site or chemical enhanced solid/liquid separation using a decanter centrifuge.
Use of Amphoteric Chemistry
The primary goal of the closed-loop dewatering system was to control mud weight throughout the bore and eliminate spoiled drilling fluid disposal. The target mud weight was 9 lbs/gal (1.1 g/cm3) with a viscosity of approximately 33 seconds per quart.
Amphoteric chemistry takes advantage of both cationic and anionic functional sites. When used properly in drilling fluid, the results include shale inhibition, well-bore lubricity and improved liquid/solids separation efficiency from both the hydrocyclones and the decanter centrifuge. The first step is to inhibit the reactive clays or make them “less reactive.” The inhibition of clays is achieved with the addition of CLAY-KATCH, which causes cationic exchange with the potential reactive sites found between reactive clay layers. By satisfying these reactive sites with CLAY-KATCH, the clays become hydrophobic (i.e. water repulsive) and water is unable to attach to the clays. The second step is to protect the inhibited clays from physical breakdown. An anionic emulsion-grade friction-reducing polymer, named KEM-VIS HD, makes up the anionic group along the clay sites to form protective hydration layers to prevent further degradation of the shale particles. In effect, CLAY-KATCH creates a bridge between each clay layer, where KEM-VIS HD creates a protective wrap that encapsulates the bridged clay layers therefore being resistant to the shear forces characteristic of hydrocyclones and centrifuges.
KEM-VIS HD additions were made in the clean tank for sweeping the hole. CLAY-KATCH additions were made in the desander’s centrifugal pump suction. This location would allow cationic exchange to occur on the clay sites prior to KEM-VIS HD additions being made in the clean tank.
The additions of CLAY-KATCH and KEM-VIS HD allow the hydrocyclones and decanter centrifuge to operate more efficiently in the separation of ultrafine, silt-size particles. Another Kem-Tron anionic, emulsion-grade polymer named KAN-FLOC E50 was used to further increase the “floc” strength of the ultra-fine silt-size particles to withstand the high gravitational forces generated by the decanter centrifuge.
The Mud Reclamation and Dewatering System
The spent drilling fluid and cuttings would exit the borehole into an earthen rig-side exit pit. A trash pump was used to feed spent drilling fluid to the primary cleaning system.
The mud recycling system made its first cut using a scalping shaker. The underflow from beneath the scalping shaker was picked up by a feed pump to supply two 10-in. desander hydrocyclones. These desanders discharged solids over a second linear motion shaker, while the overflow discharged to the next compartment. The overflow from the desander was then picked up by a second feed pump used to supply 10 5-in. desilter hydrocyclones discharging solids greater than 25 microns over a third linear motion shaker, while the overflow (containing solids less than 25 micron material) discharged into the third compartment called the “clean” tank.
Consequently, based on the PSD analysis previously conducted, minimal solids removal would have occurred using a mud reclamation system exhibiting a maximum cut of 25 microns. This would have allowed a constant build-up of solids, ultimately resulting in whole mud dumping, or haul-off, and preparation of new drilling fluid. As such, a KT-1448 decanter centrifuge was installed to draw fluids from the clean tank and generated a mud weight effluent between 8.4 to 8.6 lbs/gal.
To achieve optimum solid/liquid separation, Kem-Tron utilized two specialized dewatering polymers to flocculate the colloidal solids. The primary flocculent was KAN-FLOC E50 and was introduced into the centrifuge’s pump suction to allow sufficient time for a chemical reaction to occur before being subjected to the high-G centrifuge. KAN-FLOC E50 was used throughout the bore at varying flow-rates pending on the volume of solids present. During the pullback, COLOR-KATCH 7 was used as a coagulant to give the centrifuge the ability to handle the incredible volume of solids exiting the hole.
Even though there were intermittent events in which the actual cut was adversely affected by changes in the solids loading, the goal weight of 9 lbs/gal was easily maintained. The combination of COLOR-KATCH 7 and KAN-FLOC E50 provided the necessary conditions allowing the centrifuge to produce clear, reclaimed water.
As the pipe was pulled into the hole, Kem-Tron began to draw from the primary mud system and restored the mud back to clear water. This water was fed into the clean tank and intermittently back to the primary mud system to dilute the downhole mud, as well as make-down KAN-FLOC E50 working solutions. As a result, Kem-Tron maintained the primary mud system tank and earthen pit volumes for 5.5 hours. This was accomplished through the selective use of the onsite frac tanks used to collect treated volume on an as-needed basis. Following this period, Kem-Tron began to eliminate volume exclusively into the dirty water tanks. The second frac tank was to be used to store mud processed by the centrifuge, but lacking clarity.
The third frac tank was to be used to collect mud directly pulled from the earthen pit. As the job progressed, volume was eliminated into either the clean water frac tank or the dirty water frac tank
As the pipe was initially being pulled into the hole, the clean tank mud weights continued to increase. Since centrifuge-processed fluids were no longer being discharged to the mud system (therefore no longer diluting the circulating volume), an increase in circulating mud weight was anticipated. Table 1 highlights the changes in mud weight density over time.
The pipeline was staged in seven welded sections. Approximately 18 hours after the first section of pipe was pulled into the hole, the 12,000-gal volume was pumped into the dirty mud frac tank to be treated at a later time. By adding dirty water back into the primary cleaning system, the mud weight was fully under control. Just two hours later, the rig had completed the pullback.
Based on his own experience, Brent Lane, co-owner of Parker Lane, provided some key insight regarding historical disposal costs incurred when drilling without the use of a centrifuge-equipped solids control system. Historically, Parker Lane transported approximately eight loads per day (20,000 gals) of waste drilling fluid and spoils to a local disposal site, for a low cost of $50 per load. The 10-hour round trip would incur truck transport fees of approximately $85 per hour. Approximately eight loads of fresh water are required per day at $10 per load. Finally, Parker Lane uses a specialized blend of additives to prolong drilling fluid life at an approximate cost of $80 per day. As summarized in Table 2, the total daily waste disposal expense was $1,410. Consequently, there are several intangible costs that must also be considered, including increased downtime associated with the management of truck loading and unloading, accelerated tool wear and accelerated wash-out of triplex pumps.
During the course of the trial performed by Kem-Tron, the daily operating costs averaged $350 per day. Based on the typical disposal costs, this equated to an average daily savings of approximately $1,060 (See Table 3). Even more important than these costs-savings was the fact that Parker Lane was able to reuse the cleaned drilling fluid on its next job. Based on this particular case study, the closed-loop treatment system reclaimed approximately 70 percent of the originally prepared drilling fluid.
As experienced during the case-study described above, by taking the time to match the right technology with the right chemistry, four bores were completed with no spoiled fluids being disposed. In addition, the customer was fully prepared to start the next job without preparation of a new batch of drilling mud. Though there are initial capital expenses required to create a closed-loop or zero haul off job, the savings generated will generally pay for those costs within the first year of operation, even in the most inhospitable formations. Ultimately, Parker Lane achieved an improved rate of penetration and a 100 percent closed-loop waste management and recycling system, therefore saving time, money and the environment.
Michael Rai Anderson, P.E., is president, Chuck Skillman is manager of North American business development and David Reardon is vice president of technical services at Kem-Tron Technologies.