Bentonite Hydraul – EZ
Bentonite Hydraul – EZ
Bentonite Hydraul – EZ

Horizontal Directional Drilling (HDD) has been an important technology in the west for over a decade. Among the early advantages was the ability to cross rivers with pipelines and utilities where open trench technology is impractical. With further development, HDD has become the technology of choice for most utility lines from a few centimeters to over a meter in diameter. HDD technology is now used to cross roads, airport runways, go under other utility lines, and even under buildings. HDD technology allows working through heavily commercialized and industrial areas without causing the loss of productivity form shutting down traffic or the cost of breaking up and replacing infrastructure.

HDD technology was introduced into China only few years ago. Now China is the world抯 fastest growing HDD market. The pioneers in the China market were leading foreign produced equipment manufacturers like Vermeer among others. There are now several manufacturers producing HDD machines in China. Vermeer will soon begin assembly of their machines in China as they adapt to become competitive in the local market. The introduction of advanced HDD technology has created the demand for advanced drilling fluids in China.

HDD Drilling Fluids
Drilling fluids have several important functions. They cool and lubricate the drill bit, stem and other down hole tools. The fluid also assists in sealing the sides of the bore, therefore stabilizing the borehole. Finally, drilling fluids are designed to carry the cuttings out of the hole. A good drilling fluid should provide all of these functions. More sophisticated fluids actually stabilize reactive soils or allow the transport of larger particles and stones out of the hole.

The most widely used drilling fluids for HDD applications are based on bentonite. The world抯 best performing drilling fluids are manufactured from natural western sodium bentonite from a region in western United States. These premium drilling fluids have been imported into China by Balama Prima and others. Unfortunately the high cost of imported products has led most contractors to use locally manufactured drilling fluids. Some contractors have actually tried to use water to replace drilling fluids, which usually results in costly problems.

While locally produced bentonites might be adequate for drilling simple water wells in sandy soils, they lack the properties that are important for the more sophisticated HDD technology. Chinese deposits are primarily calcium bentonite. Calcium bentonites are poor for building fluid viscosity and are characterized by high fluid loss. Most domestic bentonite reserves also have high levels of sand and grit that lead to higher maintenance cost on HDD machines.

Viscosity could be described as the flow ability of a liquid and is measured by centipoise (cps). For example, cream would have a higher viscosity than water, while honey would have a higher viscosity than cream. Good viscosity properties are the key to maintaining the proper flow of cuttings out of the borehole. The yield of drilling fluids are typically compared by how many barrels (42 gal/bbl) of drilling fluid at 40-cps that one short ton (2,000 lbs) of bentonite will make. Calcium bentonites typically yield about 35-45 bbl/ton. Standard western sodium bentonite yields 90 bbl/ton minimum, while some advanced fluids yield over 200 bbl/ton. Even though calcium bentonites appear to be low cost, they might actually be more expensive when compared for actual yield.

In HDD boring, the gel strength of the drilling fluid is one of the most important properties. The gel strength is the ability of the bentonite to form a gel to suspend the cuttings in the borehole. If the cuttings are not suspended so they can be carried out, they will fall to the bottom of borehole. This leads to the cuttings packing-off the borehole, causing a loss of circulation and a build up of pressure. Ultimately, this will lead to the fluid fracturing the bore, coming to the surface, and possibly the loss of the drilling tool.

A good drilling fluid should have low fluid loss characteristics. If a drilling fluid seeps into the formation, it can amount to a costly loss of product. Perhaps the biggest problem is the fluid can actually fluidize the material in the formation causing the bore hole to collapse. Such a collapse might lead to the loss of drilling tools down hole and will certainly cause project delays. Bentonite is made up of many small platelets. In a good drilling fluid these platelets actually create a thin filter cake on sides of the bore hole preventing the excessive loss of fluid into the formation.

Chinese Advanced HDD Fluids
The dilemma facing HDD contractors was to either pay a high price for imported drilling fluids or face the prospect of lost productivity and equipment damage from using locally produced products. This problem has now been successfully tackled by the production of advanced HDD drilling fluids in China. CETCO is a world leader in manufacturing advanced HDD drilling fluids. Several years ago CETCO started a R&D program to create advanced drilling fluids using selected deposits of Chinese calcium bentonite as the chief raw material. After considerable work in processing technology and chemistry modification, high performance drilling fluids were finally produced in their Chicago R&D Laboratories.

During the last half of 2002 CETCO started plant trials at their VOLCLAY Dongming bentonite plant in Jianping, Liaoning Province. Scaling up production from laboratory scale to plant scale proved challenging. After nine months of plant scale tests and field trials, CETCO finally succeeded in producing high performance drilling fluids using Chinese calcium bentonite as a starting raw material.

Three types of bentonite based drilling fluids were developed. Drill Gel is a basic 90-bbl yield product. Hydraul-EZ is an all purpose HDD drilling product, and Super Gel X is a high yield product. The properties of these products are listed below. These properties may be used a guide for comparing and selecting drilling fluids for HDD applications.

Typical Properties of Advanced Bentonite-based Drilling Fluids

Product
Drill Gel
Hydraul-EZ
Super Gel-X®
Description
basic
all purpose
high yield
Yield (bbl/ton)
100
175
220
Fluid Loss
<15
<13
<15
Gel Strength (10min)
25
13
>10
Sand Content(%)
<2.5
<2.5
<2.5


The Hydraul-EZ and Super Gel X have some interesting characteristics that are only found in advanced drilling fluids. For example, they are highly efficient in reactive soils like clays. Clays will often expand and get sticky when they get wet. These characteristics can make drilling in clay formations quite difficult. When using simple bentonite, which is also clay, the drill bit and stem can get stuck in the sticky clay. It may become very difficult to get cuttings out of the hole. The chemistry in advanced drilling fluids actually covers the clay cuttings with a slippery coating that also reduces the swell rate. This coating allows the clay cuttings to become fluidized in the drilling fluid and be carried out of the hole.

The advanced chemistry and processing creates products that have far greater yields than a standard bentonite drilling product. These 揾igh yield? products create 5-6 times more drilling fluid per ton than the standard local bentonite drilling fluids. Even at a higher product cost per ton, the high yield results in significant cost savings for the HDD contractor.

The advanced 揳ll purpose? drilling fluids have a combination of properties that make HDD work much less risky. They are capable of drilling in almost any soil conditions. The advanced chemistry makes them suitable for drilling in sand, clay, silt, gravel, and even in formations with cobble stones. This technology allows the HDD contractor to go to a site and drill a long bore through several different types of soil with out having to change drilling fluids.

The ultimate benefit of advanced drilling fluids is improvement in efficiency and lower cost per meter drilled. These fluids allow for faster boring with fewer problems. The contractor gets more meters per day out of his equipment and crew. The low sand and grit result in less maintenance cost. Having advanced drilling fluids in China allows the HDD contractor to use the same technology that his counterparts in Europe and the USA have been successfully drilling with for several years.

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