Progressive fluids providers continue to introduce innovative applications of chemistry to produce the "perfect" drilling fluid.

For our 2004 drilling fluids roundup, we asked leading providers to describe their latest developments. Baker Hughes Inteq Drilling Fluids identified the industry's primary fluids technology drivers as:

• Changes in environmental legislation
• The desire for superior drilling performance
• The need for enhanced reservoir protection

These drivers have stimulated development of many new drilling fluid formulations and innovative additives.

Shift to water-base muds

Playing the environmental card has stimulated the most activity as many companies have produced alternatives to oil-based muds. Baroid has released its new PerformaDril water-based fluid system as an alternative to synthetic-based muds. The system was used recently to drill highly reactive smectite and mixed layer clays on a North Sea well in the Kristin Field. According to the company, where zero discharge rules apply to the use of synthetic-based fluids, the excellent inhibition and drilling performance demonstrated by the system provide another option for achieving wellbore stability. Using the system, a 4,462-ft (1,360-m) interval was drilled in a single bit run. The system helped eliminate the bit balling, tight hole, slow penetration rates and poor hole cleaning conditions typically associated with the use of water-based fluids in this area. Dilution rates were extremely low, running about two-thirds below average rates observed on offset wells. Torque levels were about 50% lower than anticipated and no differential sticking or losses occurred while drilling. The company stated that its PerformaDril system delivered excellent lubricity, comparing well with synthetic-based fluids. Cutting integrity was excellent and drilled solids were removed efficiently using shakers equipped with 200-mesh screens. The fluid exhibited good longevity, as large volumes of the fluid could be re-used on subsequent wells.

Another Baroid innovation is their Crystal-Dril clear water drilling fluid, a clay-free system designed to inhibit reactive bentonitic shales, eliminate bit balling and enhance penetration rates (ROP). The Crystal-Dril system can be formulated with fresh water, brine or produced water. According to the company, drillers using the product have consistently experienced fewer drilling days and lower operating costs associated with an in-gauge hole. Two operators have reported average reductions of 20% in openhole logging costs, particularly in coalbed natural gas wells, due to better wellbore stability. Fines settle rapidly due to the system's increased flocculation strength, helping to maintain low fluid densities and high performance drilling conditions.

Inteq's answer to environmental concerns is its recently-introduced Performax third-generation high performance water-based drilling fluid claimed to emulate the performance of emulsion-based systems. Benefits include enhanced shale inhibition via reduced pore pressure transmission, reduced clay swelling/hydration, improved cuttings integrity, high ROP and lower torque and drag. The system also contains a sealing polymer that helps to prevent differential sticking and mud losses in depleted sands.
For hostile environments, Inteq offers a number of innovative invert emulsion systems. These complement that company's Syn-tech CF system, which is Gulf of Mexico compliant for discharge.

The Geo-teq system employs a specialized synthetic base to minimize influence on geochemical parameters and avoid masking biomarkers used in geochemical analyses of crude oil. The system experiences minimal rheological changes in deepwater applications.

Magma-teq HT/HP fluid offers unique suspension properties to avoid density differentiations (barite sag) frequently encountered in deviated wells.

Synterra, is a non aqueous system used primarily on land, and offers a fluid design similar to conventional oil-base muds for more demanding operations.

Offering enhanced reservoir protection, Inteq's new Sciflow system maximizes hydrocarbon recovery by minimizing solids and fluid invasion into depleted or fractured reservoirs. The company has also developed software to determine the optimum particle size distribution necessary to bridge pore openings that may otherwise be damaged during drill-in.

Joining the water-base innovations is Newpark's FlexDrill system that combines seven performance-enhancing additives to form the basis for an effective water-based drilling fluid system. By tailoring system formulation to satisfy individual demands of specific wells, FlexDrill is both economical and efficient, according to the company, and it is a viable high-performance alternative to oil- or synthetic-based fluids. The formulation spans a wide range of drilling applications. Densities as high as 18.5 pounds per gallon (ppg) have been achieved. In the past year, more than 250 wells from 70 operators have been drilled from the Gulf Coast to Canada, including a 25,000-ft (7,625-m) Gulf of Mexico test and a 19,500-ft (5,947-m) South Texas land well. Newpark's approach was to apply R&D to enhance the performance of most standard fluids, such as lignosulfonate, lime-treated, or low PH/non-dispersed muds. The objective was to address specific performance criteria including ROP, wellbore stability, high-temperature stability and lubricity. Several of the FlexDrill products have evolved from the company's successful DeepDrill inhibitor product and system, except that they differ in product concentrations and overall mix, providing an economical fluid well-suited for deep shelf or deep gas projects. According to the company, the system offers operators cost savings because it is formulated onsite, eliminating liquid mud transportation costs and rig-time related displacements. EPA compliant, FlexDrill cuttings may be discharged into federal OCS waters.

The seven primary performance-enhancing components of the FlexDrill system include:

• LST-Md, a shale stabilizer that plasters the wellbore with a tough, thin, slick flexible coating to seal microfractures in shales.
• NewEdge, an extremely salt-tolerant, temperature stable humalite-based fluid conditioner that dramatically outperforms lignite products for rheology and fluid loss control.
• NewEase 203, a lubricant ROP enhancer that reduces torque and drag by forming lipophilic coating on surfaces, very effective for drilling soft, sticky shales with PDC bits.
• NewEase HT, high temperature calcium tolerant version of NewEase 203
• New 100N lubricity additive that inhibits shale hydration and is 100% water soluble.
• DeepDrill Inhibitor, that provides the benefits of oil-based muds with an environmentally safe water-based mud.
• FlexThin HTZ, a high temperature Zirconium complexed synthetic polymer that thins mud without dispersing it for high ROP.

Special-purpose products

Drilling Specialties Company, LLC, offers two new products Filtravis and Schmoo-B-Gone. The former is a new polymeric viscosifier and filtration control additive aimed at improving bentonitic systems. The polymer reduces bentonite consumption by 30% to 50% and PAC polymer consumption by up to 50%, thus lowering mud, transportation and storage costs, according to the company. In addition to reducing overall well costs, Filtravis can be used for applications such as boosting rheology prior to running casing, milling casing, directional and horizontal drilling, small bore drilling, top hole drilling and prehydrating bentonite for use in seawater muds. Filtravis allows for the running of ultra-low solids drilling fluids, reducing the amount of dispersants needed to control mud viscosities that result from over-use of bentonite. It may be used with standard cellulose based starch products to achieve desired filtrate control, and it eliminates the need for expensive Xanthan polymers. So far, Filtravis has been used in more than 3,000 wells in the Western Canadian basin.

Schmoo-B-Gone (SBG), despite its whimsical name, is a surfactant product intended to remove deposits of black tar, black scale and asphaltenes (Schmoo) from inside pipe and equipment used in produced water injection wells. SBG is a dispersing surfactant composition in an alkaline base used to emulsify and disperse heavy hydrocarbonaceous deposits. The deposits grow from single particles, and could be proppant, formation sand, fines, or other precipitants, but more likely they are iron sulfide dust or rust particles. These solids become oil-wet from a coating of surface-active chemicals such as corrosion inhibitors. Once oil-wet, they attract a layer of hydrocarbons that in the presence of water become sticky. The particles agglomerate and adhere to other surfaces. Larger particles settle out in tank bottoms, smaller ones are transported through the production system coating pipe and fouling equipment and the sandface itself.

SBG emulsifies the oil, which removes the layer of oil encapsulating the Schmoo particles. It then cleans and disperses these particles. With the sticky layer removed, there is a reduced risk of plugging. The emulsion breaks on its own, and enables oil recovery and waste separation, if not injected for disposal. According to the company, injectivity increases range from 25% to 40%.

Increased lubricity is the goal of Uniqema's new Esta-Dril L100 additive. The company developed the new lubricant especially for operators that want to use water-based muds as a substitute for oil-base or emulsion muds. The technology can be relied on to deliver a high level of lubricity without risk of breakdown at pH levels typically found in muds containing as much as 50% (by volume) of sodium silicate. In deeper wells where CaCl is the preferred additive to reduce solidification of drilling mud, Esta-Dril L100 serves to maximize lubricity properties and remain functional as the pH of oil-based drilling fluid is raised.

Deepwater challenges

The deepwater Gulf of Mexico, which recently witnessed the drilling of a well in 10,011 ft (3,052 m) of water on ChevronTexaco's Toledo well in Alaminos Canyon Block 951, presents many challenges to drilling fluids providers. From M-I comes word of a new flat rheology synthetic-based drilling fluid that, unlike conventional invert emulsion systems, exhibits a consistently flat rheology, even in the deepwater environment. The new fluid, called Rheliant, has demonstrated promising performance characteristics in field trials in the deepwater Gulf of Mexico, according to the company.

Owing to its balanced yield point, which translates into efficient hole cleaning across a broad spectrum of downhole temperatures, the new system delivered average rates of penetration some 30 ft/hr higher than the conventional synthetic-base drilling fluids employed in offset wells. In its initial trial, the system drilled a 171/2-in. section at ROPs as high as 150 ft/hr (45.7 m/hr) with zero losses. The system also exhibited excellent displacement, low dilution rates, and reduced requirements for chemical treatment. In addition, equivalent circulating densities (ECD) values were less than offset wells. The system represents a new generation in synthetic-base drilling fluid technology by providing rheology properties, especially yield point, low shear rates and gel strengths, that are independent of temperature. This provides a clear indication of how the mud system will function over a wide range of temperatures, including seafloor, bottomhole circulating and flowline temperatures. The major technical benefit of the new system is that while surface rheology numbers may at first appear higher than usual, the flat rheology profile allows the fluid to deliver consistent downhole rheology parameters.

Engineered with lower clay content and employing newly developed emulsifiers, rheology modifiers and viscosifiers, the system was designed to address issues specific with drilling deepwater wells using synthetic-base drilling fluids. In deepwater, the cold temperatures in the riser elevate the viscosities and gel strengths of most standard invert emulsion drilling fluids. Further, operations such as tripping and breaking circulation result in greater surge pressures, which all-too-often fracture the formation leading to whole mud losses. While both performance and environmental characteristics make synthetic-base fluids ideal for the deepwater, whole losses of these premium fluids can be prohibitively expensive. The newly engineered system appears to overcome this concern by maintaining a lower rheology at cold temperatures when compared to other synthetic-base drilling fluids.

Many conventional synthetic-base fluids address cold water issues simply by lowering the viscosity. Doing so means the overall rheological profile will decrease in proportion with lowering temperatures. Simply lowering the viscosity does not take into consideration other performance issues common to most drilling operations, such as hole cleaning, barite sag and cuttings suspension. The newly developed synthetic-base system maintains consistent 150?F (65?C ) mud properties even when confronting lower temperatures.

Why flat rheology?

With a flat rheology drilling fluid the mud properties maintain constant values at mud-line temperatures of 40?F (4?C); flowline temperatures that typically are between 55-70?F (13-21?C) in deepwater; bottomhole circulating temperatures, and the standard API 150?F (65?C) mud check temperature. Conceptually, a system behaving in this fashion can be expected to drill a well at lower equivalent circulating densities (ECD), encounter fewer problems drilling, and successfully avoid lost circulation problems. With a flat rheology system, the on-site drilling fluid engineer is able to design a fluid that can be effective under all down-hole temperatures and pressures conditions. The cold temperature rheology does not become excessive and the high-temperature bottomhole rheology parameters do not decrease to dangerous levels. Since the properties do not have to be compromised at one temperature to satisfy requirements of a different temperature elsewhere in the well, the flat rheology profile greatly simplifies the design of the drilling fluid. Often in deepwater drilling operations, the surface rheology must be reduced in order to decrease the rheology and ECD when encountering cold temperatures. Consequently, what often results is poor hole cleaning, barite sag or other down-hole drilling problems related to low rheology at bottomhole static and circulating temperatures. Conversely, adjusting the rheology upwards to compensate for higher bottom hole temperatures can lead to excessive ECD values, excessive gel strengths and pressure spikes that can break down the formation and lead to lost circulation.

Managing the rheology of conventional synthetic-base systems poses a very difficult challenge. With this new generation system, the unique flat rheology profile eliminates those difficulties and opens the door for more efficient drilling. From a hydraulics modeling standpoint, the new system allows the user to identify the optimal properties and design a mud system incorporating those properties over a broad range of temperatures. Often in deepwater, aggressive rates of penetration can lead to accumulation of cuttings in certain parts of the well. Thus, during connections the cuttings will settle around the bottom hole assembly or drill string tool joints, causing pressure spikes once the mud pumps are returned to operation. Consistent fluid properties help to avoid this problem. In the field trials, the superior cuttings transportation properties of the new system translated into smoother ECD profiles. Since the rate of cuttings removal managed to keep pace with the rate of cuttings generated, there was no accumulation of heavy cuttings in the annulus to gradually increase the ECD. In addition, since the constant yield point ensured efficient hole cleaning throughout the wellbore, pack-offs were avoided. The new system also was successful in eliminating pressure spikes on connections. During the static period, the gel strengths that develop can result in pressure build-up that can break down the formation when the pumps are re-started. Since the flat rheology profile fluid has low clay content, the gels are not excessive. Combining this property with efficient drilling practices, such as rotating the pumps prior to starting them, effectively eliminated the pressure spikes seen previously with conventional synthetic-base fluids. Most noteworthy are the higher yield points, measured at 150?F (65?C), than those observed with conventional synthetic-base drilling fluids. Thus, the high yield points at 150?F (65?C) did not translate into extremely high yield points at mud-line conditions. Accordingly, the high apparent yield point actually improved the ECD by providing superior hole cleaning performance.

Performance summary

In order to analyze drilling performance, the 24-hour average drilling rate of the new system was compared to existing data from wells using conventional synthetic-base fluids. The newly engineered system was introduced to the 135/8-in. casing interval, where offset wells recorded 24-hour average rates of penetration of 53 ft/hr (16-m/hr). With the flat rheology fluid the average increased to 83 ft/hr (25-m/hr). The average measured depth for each of these intervals is around 3,600 ft (1,098-m), translating to a time saving in excess of 24 hours of on-bottom drilling time.