Installation and Feasibility Considerations

A HDD project can be a major event, such as a significant water crossing, or a relatively minor one, such as a driveway or road crossing. Regardless of the nature of the HDD project, potential risks and problems should be identified early in the process. Many projects require extensive surface and subsurface investigations by qualified engineers to determine the feasibility and to assist the owner in preparation, planning, and design. The level of design-engineering effort for a HDD project is...

Fluid Capacity

Selecting a drill rig with an adequate fluid capacity is a key factor for supporting the production rate and avoiding stuck drill-pipe conditions. It is also important to properly match the fluid mixing and cleaning equipment with the drill-rig fluid capacity. If the mixing and cleaning equipment is undersized, the drill rig cannot reach optimum production rates because the drilled solids cannot be pumped out of the bore hole and cleaned as fast as the drill is capable of advancing. Likewise, a...

Geotechnical Aspects

The earth material and subsurface stratification at the HDD crossing are the geot-echnical classifications of interest. Earth material is the type and condition of the soil material at the site. Subsurface stratification defines how the earth material is distributed throughout the site. For HDD projects soil and rock are the broad categories for earth material. Soil particles vary in size. They may contain water or air in the interstitial spaces and may be excavated without drilling or...

Polymers

Polymers are often used in drilling fluids to improve the properties of the bentonite. This improvement typically involves increasing the yield. The polymers reduce the amount of dry bentonite required to produce a given amount of drilling fluid. When used in drilling fluids, Wyoming bentonite yields in excess of 85 barrels per ton of material. The addition of polymers to produce high-yield bentonite can increase the yield to 200 barrels per ton of material. Polymers are long-chain molecules...

Tie Ins and Connections

Here are some guidelines for tie-ins 1. Trenching should be used to join sections of conduits installed by the directional boring method. 2. An additional pipe length, sufficiently long to join to the next segment, should be pulled into the entrance pit. The length of this pipe should not damage or interfere with the subsequent drilling of the next leg. The contractor should leave a minimum of 3 feet of conduit above the ground on both sides of the bore hole. 3. In the case of a PE pipe,...

Laboratory Classification

Coarse-grained soils (more than 50 retained on a No. 200 sieve Gravels (more than 50 of coarse fraction retained on No. 4 sieve) Sands (50 or more of coarse fraction passes No. 4 sieve) GW Well-graded gravels or gravel-sand mixtures, little or no fines. GP Poorly graded gravels or gravelly sands, little or no fines. GM Silty gravels, gravel-sand-silt mixtures. GC Clayey gravels, gravel-sand-clay mixtures. SW Well-graded sands or gravelly sands, little or no fines. SP Poorly graded sands or...

Product Pipe Pull Loads

Product-pipe pull loads are calculated based on an analysis of the designed bore profile or the actual pilot hole. Figure 6-1 is an example of a bore profile plotted in the vertical and horizontal planes with horizontal pipe length along the x-axis and vertical distance from the reference line along the y-axis. The entire bore path is made up of straight and or curved sections. The bore path should comprise the fewest number of sections possible. However, the design can include as many sections...

Topographic and Hydrographie Considerations

The site topography is another key factor to consider for HDD projects. The key information is the site's surface configuration. It allows definition of the obstacle to be crossed and provides a basis for decisions concerning the arrangement of construction operations. The items of interest include the land and water conditions of the site or obstacle as well as any man-made features. A survey is often performed to establish a reference for the hydrographic and geotechnical data and develop...

Drilling Fluid Cleanup

It should be expected that some drilling fluid and slurry will escape from the drill pits, and inadvertent returns are also common. These types of spills are normally small and can be easily managed with proper planning. There are a variety of materials and methods available for containing and cleanup of these spills. Hay bales, silt fences, and earth berms are typically used to contain spills. They can be cleaned up by hand or with vacuum trucks. The need for vacuum trucks depends on the...

Technical Feasibility

The technical feasibility of a HDD crossing is usually the first issue to consider. There are many factors to consider when evaluating the technical feasibility of a HDD project. Conducting a site survey, usually the first step, is important for all HDD projects and is a significant part of the HDD site characterization. The site survey should include both surface and some level of subsurface investigations. Based on the information from the site survey, plan and profile drawings are developed....

Calculating the Installation Stresses

The installation stresses experienced by product pipes are often the worst-case load events that the pipe will experience over its life. As a result, the installation stresses often dictate the material properties of the product pipe. During HDD installation the worst-case stress condition is located where tensile, bending, and hoop stresses occur at the same time. Generally these are areas of tight radius bends high tension, which is usually closer to the drill rig and high external pressure,...

Depth of Cover

The depth of cover is governed by the definition of the obstacle and the intended function of the product pipe, such as a gravity sewer. Other factors such as subsurface conditions, site features, existing utilities, and environmental concerns can have a major impact on the depth requirements. When crossing a major water body, other factors include flow characteristics of the river, the depth of scour from periodic flooding, and future channel widening or deepening. Ground characteristics such...

Preinstallation

The principal stresses of concern during the preinstallation stage are the hoop and longitudinal stresses caused by hydrostatic testing and the stress caused by the spanning distance between support rollers for the pipe. The distance between the support rollers is the free-spanning distance it is used to calculate the maximum bending moments and the allowable span distance. If you are hydrostatic-testing the pipeline, the pipe will be full of water and the additional weight must be included in...

Installation Basics

All HDD installation work should be performed according to the design documents and in accordance with any permit agency requirements. Before beginning construction activities the HDD contractor should become familiar with the work area and the technical requirements of the project plans. The project limits and controls should be identified by marking or staking prior to any construction to indicate the HDD entry and exit locations and the proposed HDD alignment, using no greater than 50-foot...

Soil Conditions

Factors that are used to determine a soil's condition and aid in its classification vary depending on the type of soil. For clay soils, the unit weight, moisture content, and Atterberg limits should be determined. For granular soils, the in situ density (SPT blow counts) and grain-size distribution should be determined. Standard procedures for measuring these characteristics are Moisture content ASTM D-2216 Atterberg limits ASTM D-4318 Standard penetration test ASTM D-1586

Drilling Fluids

Drilling fluids are commonly called drilling mud or slurry. Drilling mud is mixed on the surface and pumped down the drill string. The mud comes out at the drill bit and is either left in the annulus of the bore hole or circulated back to the surface. Drilling mud is a mixture of water, premium bentonite, and, if needed, small amounts of polymer. Bentonite is a nonhazardous material. Drilling fluids have many uses or functions. The main purposes of HDD drilling fluids are 1. To establish and...

Drilling Fluids Management Plan

The following information should be provided as part of the drilling-fluid management plan Source of fresh water for mixing the drilling mud Necessary approvals and permits are required for sources such as streams, rivers, ponds, or fire hydrants. Method of slurry containment Method of recycling drilling fluid and spoils Method of transporting drilling fluids and spoils off the site Approved disposal site for drilling mud and spoils

Pipe Stress

Installation Stress Analysis Stress at Point 3 Tensile Stress stresst3 -j stresst3 862.4psi Note that stress is less than allows tress , allowstress .9-SMYS allowstress 37800psi u so tension is within limits. return PASS if stress t3 lt allowstress t3 return FAIL otherwise RESULTtensjje3 PASS Bending Stress b3 24Rj stressb3 13342psi allowstressb3 31500psi Note that stress is less than allowstress , so bending stress is with in limits. return PASS if stress lt allowstress return FAIL otherwise...

Length

As a general rule, the drill length should be kept as short as possible to reduce the HDD project costs. However, depending on the estimated costs for alternate construction methods, this may not hold true. In the current market, it is common for HDD to be used as the primary method of construction on many projects. To date the longest HDD project has been a little over 6,000 feet. The maximum length of a bore is usually controlled by the drill-rig fluid requirements, pullback and torque...

Construction Plan

The following information should be submitted with respect to the construction plan Access requirements to the site Type and capacity of drilling rig to be used on the project including thrust and rotary torque The size of the drilling equipment should be adequate for the job. An industry rule of thumb is that the drilling rig's pull push capacity should be at least equal to twice the weight of the product to be pulled or the weight of the drilling rod in the hole, which ever is greater. It...

Entry and Exit Angles

Generally the entry angles should be held between 8 and 16 degrees from horizontal, although entry angles up to 24 degrees have been used on some projects. These boundaries are due chiefly to equipment limitations. The preferred drill path is made up of straight tangent sections before the introduction of any curves. The radius of the curve is determined by the bending characteristic of the product pipeline or in some cases the drill-rod pipe. The curve usually brings the drill-path profile to...

Planning

Often the overall project requirements have a significant impact on the HDD design. The project requirements dictate choices such as the diameter and material of the product pipe, the length and depth of the crossing, and the HDD methods and equipment to be used. Thorough and organized planning is the key to a successful HDD project. The bore path design should take into account all the important factors relating to the HDD crossing. Many of the factors that impact the HDD crossing can be...

Steel Product Pipe Stress Analysis

When pipes are installed by HDD, they often experience high tension loads, severe bending, and external fluid pressures. Often these installation loads are more severe than the design service loads. When selecting the appropriate pipe materials for a HDD installation, the designer must consider the pipe properties as well as the bore-hole profile. These two factors should be considered together in order to choose the best material and profile so that the pipeline can be installed and operated...

Groundwater

For HDD projects, the installation and in-service operation of the product pipe are often dependent on location of the free water surface. To analyze the effects of the water surface, the potential for fluctuation in the groundwater table should be determined. The potential for a perched water table should also be assessed, because the possible unchecked bore-hole flow could jeopardize the successful completion of a HDD project. Regulatory bodies are also beginning to question the effects of...

Geological Considerations

In assessing the suitability of HDD for a specific location, an understanding of the site's origin is fundamental. This is important not only to the site's effects on HDD but also to plan an effective site characterization study. Understanding the mechanism by which the site was developed, whether by aeolian airborne , colluvial gravity , alluvial river , lacustrine lake , glacial, or marine saltwater sea depo-sitional processes, will forecast the types of materials to be expected as well as...

Drilling Operations

The following list provides general rules of thumb related to the directional boring method as well as specific details regarding various stages along the installation process 1. Only trained staff should be permitted to operate the drilling equipment. They should always follow the manufacturer's operating instructions and safety practices. 2. Drilling mud pressure in the bore hole should not exceed the amount that can be supported by the overburden to prevent heaving or a hydraulic fracturing...

Alignment and Minimum Separation

In all cases the product should be installed to the alignment and elevations shown on the drawings within prespecified tolerances. However, tolerance values are application-dependent. For example, in a major river crossing a tolerance of 12 feet from the exit location along the drill-path centerline may be an acceptable value. However, this tolerance is not acceptable when installing a product line between manholes. Similarly, grade requirements for water force mains are significantly different...

Chapter Footnotes

Analysis of Theoretical Versus Actual HDD Pulling Loads. Bending Stress stress bending stress bending 13342psi External Hoop Stress stress hoopexternai stress hoopextemai 470.6psi Thermal Stress k .0000065 Tt 80 T2 50 stress thermal Bk Combined stress and limitations Combined stress is analyzed by calculating the maximum shear stress on a small element In the pipeline. The maximum shear stress should be limited to 45 of he SMYS ASME ANSI B31.4 . The maximum shear...

Slanted Face Rock Bits

Directional Drill Bits

Slanted-face rock bits are used in harder ground conditions and soft rock less than 3,500 psi that cannot easily be penetrated with thrust alone. The face of the tool usually has one or more nozzles emitting pressurized drilling fluid. In harder ground conditions, steering is accomplished by techniques such as partial rotation and release, wiggling the bit clockwise counterclockwise fishtailing while thrusting at the desired steering orientation, or by a broader arc of clockwise...

Maxi Rigs

Mobilization and Set Up lt 6 hours 2. Pilot Hole Drilling 100-400 ft hr 3. Prereaming Reaming Per Pass 100-300 ft hr 4. Product Pullback Without Reaming 200-600 ft hr 200-600 ft hr 200-600 ft hr 200-600 ft hr 200-600 ft hr 200-600 ft hr Function of material, diameter, length of sections, crew size and skill, and testing requirements. TABLE 2-5 HDD Production Rates for Various Conditions TABLE 2-5 HDD Production Rates for Various Conditions Pilot Hole Production Rate ft hr for Pipe Diameter...

Drilling and Back Reaming

The following are basic requirements for this stage of the process 1. Drilling mud should be used during drilling and back-reaming operations. Using water alone may cause the bore hole to collapse in unconsolidated soils, while in clays the use of water may cause swelling and subsequent jamming of the product. 2. Heaving may occur when attempting to back-ream too large of a hole. This can be avoided by using several pre-reams to gradually enlarge the hole to the desired diameter. 3. A swivel...

Pilot Hole Drilling

The total volume, Vpilothole, in barrels of drilling fluid consumed not available for recirculation during pilot-hole drilling can be found using the relation Q drilling fluid flow rate, barrels per minute L drilled length, feet Prate pilot hole production rate, feet per hour Fpump pumping factor, minutes per hour the actual time that the mud pump is pumping down hole Fcir pilot hole circulation loss factor The total volume, Vream, in barrels of drilling fluid consumed not available for...

Tracking

In HDD applications tracking is the ability to locate the position, depth, and orientation of the drilling head during the drilling process. The ability to accurately track the drill is essential to the completion of a successful bore. The drill path is tracked by taking periodic readings of the inclination and azimuth of the leading edge of the drill string. Readings are recorded with a probe that is inserted in the drill collar as close as possible to the drill bit. The three most common type...

Identification of Risks

Horizontal Drill Path Design

An important part of the planning and design phase of a HDD project is to identify and avoid or at least reduce possible risks. If potential risks cannot be avoided or reduced, the crossing alternative should be closely evaluated and other alternatives considered. A decision has to be made as to whether to accept the risks or select another crossing option. Even with the best planning and design efforts unexpected risks can occur. Experienced and qualified contractors are well equipped to solve...

Pullback

Once the drilled hole is enlarged, the product pipeline can be pulled through it. The pipeline is prefabricated and usually tested on the bank opposite the drilling rig. A reamer is attached to the drill string and then connected to the pipeline pull head via a swivel. The swivel prevents any translation of the reamer's rotation into the pipeline string, allowing for a smooth pull into the drilled hole. The product pipe has to be supported for the pullback operation. This is usually...

Ductile Iron Product Pipe

Inch Ductile Iron Pipe Laying

As can be seen in the preceding section, in many ways plastic pipe and HDD seem to be made for one another. As HDD became commonplace in the underground TABLE 4-9 Typical PVC Safe Pulling Loads Straight Pull Stress 1800 psi Bending Pull Stress 800 psi Typical PVC Safe Pulling Force cross sectional area x pull stress TABLE 4-9 Typical PVC Safe Pulling Loads construction market during the 1990s, plastic pipe was the material installed most often. Today, the use of plastic pipe in HDD installation...

Work Area Conditions

Horizontal Directional Drilling Plan

The area required for the HDD rig must be sufficient for the rig and its ancillary equipment. In general, the size of the required area will depend upon the size of the HDD crossing, including length of bore and diameter of the pipe to be installed. The length of the crossing and diameter of the product pipe will dictate the size of the drill rig and the drilling equipment to be used. See Table 1-3 for the recommended workspace requirements for different classes of drill rigs. Preferably each...

HDD Technology and Equipment

A basic horizontal-directional drill-rig is illustrated in Figure 3-1. Horizontal directional drilling is accomplished using a drill rig. It services a bottom-hole assembly BHA that is responsible for creating a curved bore hole. The BHA consists of a drilling tool that is capable of creating a curved bore hole and a guidance system that locates the bore hole and directs changes in the trajectory. There is a variety of HDD rigs currently in use. Table 1-3 lists the three general categories of...

Applications

HDD is a multi-billion-dollar annual industry with hundreds of contractors and thousands of drilling rigs operating on five continents. HDD in North America has grown from 12 operational units in 1984 to thousands of units today. This rapid growth is attributed at least partially to 1. The increasing traffic-control and restoration costs involved in the installation of utility conduits and pipes in congested urban areas and the need to dig around existing utilities. 2. The increased awareness...

Permitting and Easements

As in traditional pipeline or utility construction projects, there are numerous federal, state, and local agencies that may be involved in HDD crossings. Large projects or projects on federal land typically require a lead agency to coordinate the permit-application process and to monitor construction compliance with the applicable permits. The U.S, Bureau of Land Management, U.S. Forest Service, U.S. Fish and Wildlife, U.S. Army Corps of Engineers, and the Federal Energy Regulatory Commission...

Economic Feasibility

Once the technical feasibility of a prospective HDD installation has been established, its economic feasibility can be assessed. This assessment includes estimating the economics or costs of the HDD project as well as considering how the technical aspects of the project may impact project bids and contracts. This assessment can be accomplished by comparing it to the costs of past similar installations or by getting estimates or preliminary bids from qualified HDD contractors. HDD crossings that...

Breakaway Pulling Heads

Recent reports from several natural-gas utility companies reveal concerns regarding failure experiences on HDPE pipes installed by horizontal directional drilling. These failures were attributed to deformation of the pipe due to the use of excessive pulling force during installation. A mitigation measure adopted by some gas companies involves the use of breakaway swivels to limit the amount of force used when pulling PE products. The weak link used can be either a small-diameter pipe but same...

Drilling and Steering

Drill Head Steering Tool

Drilling curved and horizontal bore holes requires specialized drilling equipment. This equipment is contained in a bottom-hole assembly BHA that consists of a drilling tool, a bent subassembly, and a steering tracking tool. Pilot-hole directional control is achieved by using a nonrotating drill string with an asymmetrical leading edge. The asymmetry of the leading edge results in a steering bias. When a change of direction is required, the drill string is rotated so that the direction of the...

Hdd Drilling Opener

Hdd Pulling Swivel

Torque Reamer duct and nuts and bolts passed through a pull chain. This put the entire load of the pull on the holes drilled through the duct and was for that reason quite ineffective. Today, every duct manufacturer recommends the use of a puller that distributes the load around the entire circumference of the duct. The most common type of puller has a set of wedge-shaped teeth on a conical mandrel that is inserted inside the end of the duct. As the mandrel is pulled forward, it forces the...

Distribution of Particle Sizes

The distribution of particle sizes larger then 0.075 mm No. 200 sieve is determined by sieving, while the distribution of smaller particle sizes is determined by a sedimentation process. For the USCS, rock fragments or soil particles are defined as follows 1. Boulders particles of rock that will not pass a 12-inch-square opening. 2. Cobbles particles of rock that will pass a 12-inch-square opening and be retained on a 3-inch U.S. standard sieve. 3. Gravel particles of rock that will pass a...

Equipment Setup and Site Layout

The following are guidelines for setting up equipment on the site 1. Sufficient space is required on the rig side to safely set up and operate the equipment. The workspace required depends on the type of rig used. A working space of similar dimensions to that on the rig side should be allocated on the pipe side, in case you need to move the rig and attempt drilling from this end of the crossing. 2. If at all possible the crossing should be planned to ensure that drilling proceeds downhill,...

Required Workspace

While selecting a larger class of drill rig may seem appropriate, you need to consider the available workspace as well as operating costs. The proper method is to balance the required power, pullback, torque, and fluid handling capacity with the drill rig that can do the HDD crossing reliably. The rig should be capable of doing most of the anticipated jobs without reaching the limits of the drill system's capabilities. The best drill system will perform the job while staying well within its...

Down Hole Mud Motors

Downhole Mud Motor

With high-capacity pumps and HDD rigs with higher drilling-fluid-flow capacities, the down-hole mud motor has become the tool of choice for directionally drilling in rock. The drilling-fluid requirements to power mud motors are much higher than for mixing and transporting cuttings however, the majority of the fluid can be recycled and reused. The important factors in classifying mud motors for HDD applications are the output torque, fluid volume requirements, and length. Length is important...

Project Contract Documents Plans and Specifications

The contract is important for all HDD projects. It is important that HDD contractors understand the project contract documents and technical specifications before starting any work. This will help reduce unexpected risks and delays in the project. It is very difficult to identify all the potential risks during the planning and design phase of any HDD project. The contract documents should address the risks of a failed bore due to unforeseen problems, and a shared-risk contingency plan should be...

General Information

When planning HDD crossings with plastic pipe, the primary concern for owners is usually whether the product pipe can safely handle the stresses and the required pullback loads. As discussed in Chapter 4, after selecting the required DR for the product pipe the next step is to determine if the DR selected can handle the installation loads. As with steel product pipe, plastic pipe, when installed by HDD, may experience high-tension loads, severe bending, and external fluid pressures. Usually...

Figure Typical HDD Drill

Vermeer Drill Rigs

Must be anchored to provide a reaction against which the mechanical system can operate. Anchoring is typically done by driving stakes through openings at the front of the rig, attaching the rig to a buried weight, or simply attaching the rig to a large, heavy piece of equipment on the surface. The drill rig must provide sufficient thrust and the drill pipe sufficient strength to advance the drill string the full length of the proposed bore hole and sufficient pulling force to retract casing...

Rock Conditions

Factors that are used to determine the condition of rock are measurements of unit weight, hardness, and in situ conditions. Rock hardness has been correlated with the unconfined compressive strength of rock specimens. Table 2-31 lists the hardness of rock as a function of the unconfined compressive strength. Because the unconfined compressive strength is performed on small rock specimens, it often does not represent the actual condition of in situ rock. This is caused by the presence of joints,...

HDD Design Basics

The planning, design, and construction of HDD projects requires a specialized knowledge of pipeline construction methods and HDD equipment and technology. While Chapter 3 provides information about HDD equipment, this chapter discusses HDD design and installation. The planning and design of a HDD crossing should focus on meeting the requirements of the owner while keeping the project costs as low as possible. Many factors have an impact on HDD costs, but the most important is the crossing...

Bore Path Profile

The procedures for designing the bore path for plastic pipe are basically the same as discussed for steel pipe in Chapter 6. The first step in calculating the estimated pulling loads is to develop the input data, such as pipe properties, DR, drilling-fluid properties, and code design factors, that will be used in the calculations. Examples of typically required input data are provided in the examples in this chapter. The bore path is selected based on the profile required to successfully cross...

Safety

Each bidder should submit a copy of the company safety manual, including Operating procedures that comply with applicable regulations, including shoring of pits and excavations when required Emergency procedures that comply with applicable regulations for inadvertently boring into natural gas lines, live power cables, water mains, sewer lines, or fiberoptic cables Emergency evacuation plan in case of an injury The drilling unit must be equipped with an electrical strike safety package. The...

Unified Classification System for Soil Type

The type of soil at a crossing site should be classified using a standard classification system. The purpose of a soil-classification system is to provide the engineer with a method to predict the behavior of the soil for engineering projects. For a soil-classification system to be effective in the HDD industry, it must be widely used, simple, inexpensive, and based on parameters that impact the HDD process. The unified soil-classification system USCS satisfies these standards. It is described...

HDD Down Hole Equipment

Hdd Pipe Reamer

Unglamorous as down-hole equipment may be, these tools perform their vital functions underground and out of sight, and no drill rig can function without them. Bits and reamers, transmitter housings, swivels and pulling heads all are down-hole tools necessary to make HDD possible. Bits cut through soil to make pilot holes. The slant-face bits still used by most drillers making utility installations provide the steering ability that makes the HDD rigs directional. Reamers enlarge pilot holes to...

Axial Tensile Stress

The maximum tensile stress during pullback is the sum of the tensile stress due to the pullback force, including the hydrokinetic force, and the tensile stress resulting from the bending of the pipe. The average axial stress acting on the pipe cross-section at points 1, 2, 3, or 4 is given by Tx DR2 E D x 2 , -TT Equation 7-16 ox average outer-fiber axial tensile stress at corresponding point in psi Tx tensile force at corresponding point in foot-pounds D pipe outside diameter in inches DR pipe...

Drilling Fluid Collection and Disposal

The collection and handling of drilling fluids and inadvertent returns is perhaps one of the most debated topics in the HDD community in North America. On one side the industry realizes the need to keep drilling fluids out of streams, streets, and municipal sewer lines. On the other hand, tough new regulations in some states e.g., California present HDD contractors with escalating expenses. Owners need to adopt an approach that addresses environmental concerns while at the same time avoiding...

Resistance to External Collapse Pressure During Pullback Installation

The allowable external buckling-pressure equation, Equation 4-14, with the appropriate time-dependent modulus value can be used to calculate the pipe's resistance to the external pressure during pullback with proper reductions. The reduction occurs due to ovality and the hoop strain created by the pulling force. If the pipe is empty, the buoyant force will cause a reduction in the vertical diameter. The deflection fraction due to buoyancy can be calculated using Equation 4-13. This value can be...

Mud Motor Rock Bits

Horizontal Drilling Contractors

Increase width, length, and or angle for more aggressive steering May be modified by adding teeth, tapers, etc. to match conditions Small surface steering area abrasion and impact resistant cutters Refer to International Association of Drilling Contractors for numbering schemes Refer to International Association of Drilling Contractors for numbering schemes No moving parts Sealed Bearing Roller-cone Tungsten Carbide Inserts Sealed Bearing Roller-cone Drag Bit Polycrystal Diamond Compact PDC...

Torque and RPM Considerations

Torque and drill-pipe rotational speed RPM are the drill-rig characteristics that determine possible production rates. Torque and rotational speed are a measure of the drive-spindle horsepower, delivered through the drill string, available at the drill bit or reamer. This is not the case when auxiliary power is used, such as a down-hole mud motor. The basic equation for horsepower is HP spindle horsepower T spindle torque, foot-pounds RPM spindle speed As can be seen in the above equation,...

Pilot Hole

The first step in a HDD installation is to drill a carefully guided pilot hole that delivers the drill bit and bore head to the surface at the specified exit point. The bore is launched from the surface, and the pilot bore proceeds downward at an angle until the necessary depth is reached. A small-diameter drill string penetrates the ground at a prescribed entry point and the design entry angle, normally between 8 and 16 degrees. To help prevent the drill rod from deflecting upward or to the...

HDD Risk Identification

Potential risks that are a part of all HDD projects include a failure to complete the bore, safety of the public and workers, environmental issues, damage to surface structures, and striking other underground structures. Risk reduction is the attempt to identify potential risks during the planning and design phase so that they may be eliminated or reduced. A risk contingency plan is often used by the engineer and or contractor to help identify the major risks and develop general plans and...

Reaming

Once the pilot hole is successfully drilled, the hole is often enlarged to a suitable diameter for the product pipeline. For instance, if the pipeline to be installed is 8 inches in diameter, the hole may be enlarged to 12 inches or more. This is accomplished by reaming the hole to successively larger diameters. Generally the reamer is attached to the drill string on the bank opposite the drilling rig, rotated, and pulled pushed in some instances back through the pilot hole. Joints of drill...

Hard RockMud Motor

Hard-rock bits are used in ground conditions ranging from hard soil to hard rock with compressive strengths up to 40,000 psi or higher. When drilling in rock or hard soils, the drill bit cannot be pushed without rotation. In these soil conditions aggressive cutting bits and mud motors are used. Hard-rock or mud motor bits are classified as tri-cone bits with mill-tooth and tungsten-carbide inserts, drag bits, and polycrystal-diamond-compact PDC drag bits. For rock drilling positive-displacement...

Frictional Resistance

Pipe Bending Formula

Pipe resistance to pullback in the bore hole depends primarily on the frictional force created between the pipe and the hole or the pipe and the ground surface in the entry area, the frictional drag between pipe and drilling slurry, the capstan effect at bends, and the weight of the pipe. Equation 7-4 gives the frictional resistance or required pulling force for pipe pulled in straight, level bores or across level ground Figure 7-2 . FP pulling force in pounds coefficient of friction between...

Average Radius of Curvature

The average radius of curvature for a pipe segment, such as point 1 to point 2 or point 3 to point 4 in Figure 7-1, may be estimated from the entry and exit angles and the depth of the bore by and the radius of curvature at any point along the bore path may be estimated by Ravg average radius of curvature along the bore-path segment in feet H depth of the bore beneath the surface in feet O bore entry and exit angle to the surface in radians degrees R local radius of curvature along the bore...

Pulling Back

The total volume, Vpua, in barrels of drilling fluid consumed not available for recirculation during pull back pipe installation is given by drilling fluid flow rate, barrels per minute drilled length, feet estimated pullback penetration rate, feet per minute pullback circulation loss factor Using the above equations, the total estimated volume of drilling fluid consumed Vconsumed is the sum of Vpiiothole, Vream, Vpuii, and the fluid system line fill. The fluid system line fill is the volume of...

Product Pipe Considerations

During the design process an evaluation of the product to be installed by HDD is critical. The design should evaluate the product pipe's suitability for the installation loads, corrosion conditions, pull-in installation, and intended function. In general, the pipe to be installed must be capable of being joined together continuously while maintaining sufficient strength to resist the high tensile stresses imposed during the pullback operation. The primary criterion governing the specification...

Operating Stresses

The operating stresses of concern include a combination of the longitudinal curvature stresses, external pressure stresses, and hoop and longitudinal stresses mentioned above. For operating stresses, the maximum working pressure of the pipeline is used to calculate the longitudinal and hoop stresses that will be imposed during service. After determining the individual and combined stresses, they are compared with the allowable stress limits for the product pipe. For example, ASME B31.8 provides...

Steel Product Pipe

Steel-pipeline properties such as wall thickness and material grade, as well as the bore path profiles, must be specified so the pipeline can be installed and operated without risk of damage. During HDD installation the pipeline is subjected to tension required to pull the pipe into the pilot hole and around curved sections. The tension comes from the drag due to the friction between pipe and bore hole and the fluid drag caused by pulling the pipe through the viscous drilling mud trapped in the...

Calculating the Pull Loads

Horizontal Directional Drilling Crossing

The first step in calculating the estimated pulling loads is to develop the input data that will be used in the calculations. This data includes the product-pipe material properties, the drilling-fluid properties, and any code or design factors that are applicable. An example of the input data required for calculating estimated pulling loads is provided in Example 6-1 later in this chapter. Defining the Bore Path The next step is to define the bore path for the crossing. Figure 6-1 defines a...

Transmitter Housings

Bit location and data needed to guide the drill path are relayed to the drilling crew by a radio transmitter located behind the drill bit. While the transmitter itself isn't classified as a down-hole tool, the housing it's in is one of the most important down-hole components, protecting the tool from the stresses of drilling and allowing cooling fluid to flow around the transmitter. The newest radio-transmitter housings are made of more durable materials to resist cracking, and their designs...

Cable and Pipe Pulling Devices

Cable grips are used for pulling cables and small-diameter pipe, usually 4 inches or less. Cable grips are attached to the outside of the pipe and can be taped or tied with clamps at the end to prevent them from pulling off. When using cable grips for pulling pipe, the normal practice is to use a solid insert that is at least twice as long as the inside diameter of the pipe in order to help prevent the pipe from collapsing. Duct pullers are also a very important part of pullback operation. The...

Percussive Drilling

One of the most common misconceptions about a percussive hammer is that it is not a proven method for rock drilling. Percussive hammers have been around for decades in the vertical industry. There are three basic categories rotary, percussive drifter, and down-the-hole percussive hammer. Rotary drill equipment was covered in the previous sections. Drifter percussive drills do not rely on high thrust or high torque for the cutting action they operate on the percussive energy that comes from a...

Bore Path Geometry for Plastic Pipe

Hdd Pipe Reamer

In addition to the bore-path-geometry methods discussed for steel pipe in Chapter 6, other methods from ASTM1 and plastic pipe organizations1 are often used for plastic-pipe crossings. These methods use an average radius of curvature for the pipe section from the entrance of the bore hole to the end of the curve. Figure 7-1 defines a typical bore-path profile used for plastic-pipe crossings. The values are assigned based on the profile required to successfully cross the obstacle while reaching...

Subsurface Conditions and Considerations

The decision to use the HDD method for a crossing should be based on an understanding of the HDD process and the crossing site's characteristics. The natural and man-made features in the area will dictate the design for the HDD crossing. After determining if the surface conditions are suitable for HDD construction, the next item to consider is the subsurface conditions. A vital element of many HDD design projects is a comprehensive geotechnical survey to identify soil formations at the...

Directional Drilling Noise

Noise is often an area of concern in congested urban areas. Many local areas do not have noise ordinances that establish limits such as maximum decibel levels. In fact, there does not seem to be any consensus on what level of noise is a problem. If the regulatory agency has noise-control provisions, the contractor may use the manufacturer's specifications for the equipment and or measure noise levels at various distances. Based on the data, noise-abatement equipment can be used as necessary to...

Geotechnical Investigation

The information from the geotechnical survey is used to select the crossing route, drilling tools, procedures, and the drill-path design. The level of effort required for the geotechnical investigation depends on several factors, such as the pipe diameter, bore length, and the nature of the HDD crossing. For many HDD projects, especially in municipal areas, the subsurface investigation consists primarily of research of existing geotechnical data. Due to the costs and the congested nature of...

Pullback Loads

HDD drill rigs can exert extensive pull forces. Most of the force is applied to the cutting face of the reamer. As discussed in Chapter 6, it is a difficult task to estimate what portion of the total pullback force is being transmitted to the product pipeline. The pulling force, which overcomes the combined frictional drag, capstan effect, and hydrokinetic drag, is applied to the first joint of plastic pipe. The axial tensile stress intensifies over the length of the pull. The duration of the...

Disadvantages

Hdpe Pipe Accessories

No disturbance in water body or wetland. Ground disturbance of drilling and target areas. Fractures in the subsurface may release drilling fluids into the water body. Greatly reduces the clean-up and reclamation efforts and costs. Largely dependent upon the subsurface conditions. Specialized equipment and crews required. Limits on the stress radius of the pipe to be installed. Another factor in the increased popularity of HDD for municipal applications is the acceptance of HDPE pipe for water...

SMYS fl fs

F maximum allowable pull force, pounds R design radius of curvature, feet E modulus of elasticity, psi A cross-sectional pipe area, inches2 D pipe outside diameter, inches SMYS specified minimum yield strength of the steel, psi fl maximum load factor fs safety factor TABLE 4-1 Typical Steel Pipe Specification for HDD Steel pipe shall conform to API 5L X52 specifications. The pipe shall be seamless or electric resistance welded ERW steel pipe as specified in ASME B31.8. Butt-weld fittings shall...

Surfactants

Surfactants, or soaps, are wetting agents that are used to break clay water bonds and disperse clay particles to stop or break up clumps. Surfactants are usually used in sticky clays. TABLE 5-3 Applications of Bentonite-Based Drilling Fluids Courtesy of DCCA Bore Gel Specially blended system using high yielding Wyoming sodium bentonite. When mixed with fresh water, develops an easy to pump slurry with desirable properties for HDD drilling Quick-Gel Viscosifier and gallant. Easy to mix in fresh...

Examples

Example 7-1 is an example of the calculations for pullback force, stress, and a safety factor for a HDD crossing with a 14-inch DR 9 PE pipe. All the calculations produced acceptable results. Example 7-2 is an example of the calculations for an 8.625-inch DR 11 PE pipe. With these calculations the pipe fails to meet acceptable conditions in several areas. One key point to notice is that it fails to provide for allowable pull force and stress. Example 7-3 has the same conditions as Example 7-2...

The HDD Process

Drilling Install Pipelines

The basic components of a horizontal directional drilling system include Drill pipe and downhole tools, including bits and back reamers Drilling fluid mixing or recycling system The HDD rig is connected to the cutting bit by the drill string, which is made up individual joints of pipe. Back reamers are used to increase the diameter of the pilot hole to the required size to accommodate the diameter of the pipe to be installed. The drilling fluid, commonly known as mud, plays an essential role in...

Design Radius of Curvature

Hdpe Pipe Curve Radius

Determining the entry and exit points, the depths that must be achieved, and direction changes for the drill path are all major parts of the planning process. One of the keys to these calculations is the bend radius of the drill rod and or the product pipe. Bend radius is often misunderstood. It is often confused with the number of feet needed to make a 90-degree turn. Bend radius is defined as the forward distance required for a drill string to make a 90-degree turn see Figure 4-2 ....

Risk Mitigation

Sharing risk with the contractor can significantly reduce the average bid price on a project. This is particularly true in underground construction. Factors that should be addressed in contracts involving HDD work may include provisions for ground or water conditions that are different from what is expected for the project and a walk-away provision. Adequate geotechnical information is invaluable in underground construction and can help to reduce the contractor's risk. However, even with good...

Figure Typical Downhole Equipment Diagram

Competitive, drillers are always looking for new down-hole tool designs to increase their production and decrease their downtime. Performance of down-hole tools directly affects productivity. And selecting the best tools for the machine on which they will be used and the soil conditions often makes the difference between success and failure of a directional-drilling installation. With the choices of down-hole tools available, a driller's objective is to match the tool to the job conditions. The...

Pulling Force

Most HDD crossings are comprised of a combination of straight sections and bends, and Equations 7-4 and 7-5 have to be applied to each straight section and bend in the bore hole. The corresponding loads may be estimated by the following equations. For calculating the estimated peak force on the product pipe the load is calculated at four points, as shown in Figure 7-1. The greatest load will be experienced at point 4. The loads may be estimated by using the following equations T1 exp Va a Va w...

Reamers and Hole Openers

New reamers offer drillers more choices than ever for the right tool for varying soil conditions, and reamers are available in more sizes than in the past. Low-torque tools require less force to cut through soils and mix fluid slurry. New reamer designs also have increased fluid-mixing efficiency. Reamers are used to enlarge the bore sufficiently to facilitate installation of the product. The reamer must be capable of displacing the native material or reducing it to manageable cuttings, mixing...

Hydrokinetic Pressure

During pullback the pipe experiences resistance from the drag of the drilling fluid. This develops a pressure gradient that corresponds to the force required to exhaust the drilling fluid out of the hole towards the pipe entry area. This is called hydro-kinetic force, and it is difficult to estimate. The drag force may be estimated by considering a balance of the forces acting on the fluid annulus in the bore hole due to the hydrokinetic pressure and the lateral shear forces acting on the pipe...

Chart Hdd Applications

Pipeline Construction Swamp

Stricter placement tolerances, as is the case in many municipal applications. Chart 1-1 lists the distribution by industry of HDD applications. As a result of the growth of HDD, the marketplace is providing a wide range of HDD units and support equipment. HDD rigs range from mini-rigs that are usually used for the installation of smaller pipe and conduits 2 inches to maxi-rigs that are capable of installing 48-inch pipelines. The length of pipe that can be installed by HDD is determined by many...

Drilling Fluid System

Typical Fluid System

For HDD construction the primary impact on the environment revolves around the use of drilling fluids. Many regulatory problems result from a misunderstanding of the effects of drilling fluids. Informing the regulatory agencies about the purpose and composition of HDD drilling fluids is important for many successful HDD projects1. For many HDD projects the drilling fluid system comprises a substantial portion of the HDD equipment and cost. The system is composed of both the equipment and the...

Work Plan

Establishing a work plan is an important function of a HDD project. The work plan should identify Table 5-1 is an example of a project management format that is often used in setting up a simple HDD project, and Table 5-2 is an example for a major HDD project. The work plan should contain a task outline. A good task outline consists of a brief summary of the scope of work required to complete the project described in the contract. The following can be used to evaluate the suitability of a task...

Plastic Product Pipe

Ovality Compensation Factor

Over the last thirty years, the underground piping market in North America has seen tremendous growth in the use of thermoplastic materials. Benefits such as corrosion resistance, improved hydraulics, and reduced installation costs have been paying large dividends for owners of natural gas, water, and sanitary and storm sewer systems. The most widely used of this group of non-metallic polymers is polyvinyl chloride, also known as PVC. The second most prominent thermoplastic used in the...