by Martin Cherrington, Cherrington Corporation

Martin Cherrington conceived the use of Horizontal Directional Drilling as a practical alternative to conventional trenching methods beginning in the 1960’s. HDD, as it would become known, would ultimately revolutionize the way the Construction Industry would come to install underground utilities and pipelines in cities and under large natural obstacles like the Mississippi River.

Cherrington worked with his father, a construction industry contractor, early in his career where he gained experience working on dams, tunnels, pipelines, telephone and power cable projects. Construction projects during this period occasionally involved non-directionally controlled boring or drilling to place a pipeline or telecommunication conduit across roads or highways but only when conventional trenching methods could not be used to complete the project. Directional drilling methods and technologies that would one day make Horizontal "Directional" Drilling possible, as we know it today, were still in their early stages of development in the oil and gas industry.

While working for a contractor in the Los Angeles area in 1963, Cherrington realized that there might be potential for using drilling technology to greatly enhance the efficiency of placing cables and conduits underground. Cherrington was a foreman on a project to lay telephone cable by open trench method in a residential area. Just down the street another contractor moved in several weeks later to also lay cable similar in size and length. The difference, however, was that this contractor used drilling rather than trenching to install the cables and conduits. Not only did that contractor arrive two weeks after Cherrington’s project had commenced but finished two weeks sooner! Furthermore, the other contractor’s project was significantly cleaner during and after construction. This observation would spark an idea that ultimately would launch a whole new industry, Horizontal Directional Drilling.

In 1964, Cherrington built his first drill rig and formed Titan Contractors a company specializing in utility road boring in Sacramento, California. A unique combination of events contributed to Titan Contractors initial success. A building boom in Sacramento coupled with a national movement to clean up America sponsored by Lady Bird Johnson, President Lyndon Johnson's wife, motivated the local community and its utilities take action. Unsightly utility lines would need to be placed underground to free residential neighborhoods of utility poles and cables that had become an eyesore in every backyard in America. To comply with the First Lady's beautification decree, the County of Sacramento mandated that all utilities be placed underground. With streets, sidewalks, curbs and gutters already in place in many new subdivisions, Titan Contractors was presented a unique business opportunity. The local power company, Sacramento Municipal Utility District (SMUD) contracted Titan Contractors to drill in new underground cables throughout its service area. The workload volume was so great that several new drilling rigs had to be built to keep up with the demand.

In spite of Titan’s success, sources of funds for research and development to improve the technology were limited or non-existent. AT&T’s Western Electric experimented with some crude directional control methods but the techniques never became commercial. Titan therefore reinvested profits from its developing business to build more rigs, create downhole tools and experiment with new technology that would ultimately contribute to horizontal drilling technology becoming an accepted construction technique.

The company had to compete with the well-established and accepted companies that performed open trench services. As the building boom subsided in Sacramento, Titan Contractors found it difficult to convince local permitting authorities to favor Horizontal Drilling over open trench methods to cross streets and highways. Only in cases of heavily traveled areas did permitting agencies allow an alternate approach. Even then the issued permit would call out auger boring or jack and tunnel methods rather than drilling because of the lack of familiarity of the new technology. Permitting Agencies objected to drilling methods because it was believed that drilling fluids would soften, damage and wash out crossed roadbeds. This seemed to be a conundrum because most trenched streets leave a variety of scars in the form of dips, bumps and potholes for motorist to contend with forever. All horizontally drilled sites, on the other hand, never showed any signs that construction had occurred and never needed to be repaired. It is difficult to understand whether this was the result of the flawed logic of the local permitting agencies or the complacency with time proven existing methods. Sometimes it is difficult to change the status quo and get people to think in terms of a new paradigm.

Over the next few years Titan Contractors gained considerable experience and completed several significant projects. One such project required drilling and pulling back a power cable along a curved street 1530 feet in length. Titan used a 2000 lb push/pull rig with 500 ft-lbs of torque and 1-1/8" O.D drill pipe to drill the directional hole. Considering that no directional control technology existed for accomplishing this type of borehole, the successful completion of the project was quite remarkable. Despite achieving such a feat, there were no trade journals, professional societies or associations yet to report its significance to horizontal drilling.

In 1971, Titan Contractors was invited to look at and bid on several road crossings for PG&E (a major California gas and electric utility) near Watsonville, California just south of San Francisco. While physically investigating the potential job sites, a PG&E engineer asked Martin Cherrington to look at a site where the utility needed to cross the Pajaro River. The company was interested in a solution to take a gas line across the river without trenching it. Upon investigating the site it became obvious there would be a problem with using conventional trenching methods. The river had a steep high bank, approximately 20 to 25 feet high. The bottom half of the bank was composed of sand and the top half consisted of rich topsoil. The adjacent field supported rows of the artichokes that are a common crop for the area. On the opposite side of the river channel a small bank, 5 to 6 feet high flattened out and extended eastward 30 to 40 feet to a levee approximately 10 feet high. Beyond the levee was a field of potatoes. The bottom of the channel consisted of loose unconsolidated sand.

To trench the river, parallel double sheet pile would need to be driven deep enough so that the river bottom could be excavated sufficiently to lay the 4" gas pipeline between the piles. Once installed across the river, the trench would have to be backfilled and the piles extracted. Based on the cost of a similar project a mile down river, PG&E reasoned that a drilling operation might be a more cost effective solution.

Cherrington and PG&E initially considered driving two vertical caissons on either side of the river. One would be placed on top of the high West bank and the other just outside the East levee. The product pipe could be then drilled, bored or jacked from near the bottom of one caisson to the bottom of the other.

On his way back to Sacramento, Cherrington contemplated the problem further and realized that there might be another alternative. Experience to date had revealed a curious phenomenon that had plagued attempts to drill a straight hole from pothole to pothole on many projects. With no directional control technology available, some types of drill stem tool configurations had a tendency to drill upwards into existing substructures coming out unexpectedly in the middle of a busy street. These drill stem tools were discarded to the junk pile as design failures. Little did anyone know that they were a potential solution to a problem confronting many pipeline contractors - a way to conveniently cross major rivers without disrupting them.

With the hope of testing a revolutionary new idea using the discarded downhole drilling tools, Cherrington assembled his crew and horizontal drilling equipment and headed for the Feather River, a few miles north of Sacramento. The sand and soil characteristics of the location picked on the Feather River were similar to the Pajaro River near Watsonville. Rather than drilling across the river, it was decided to test-drill parallel to it on one bank. The entry angle for the first hole was approximately 10º from horizontal. After drilling about 60 feet, the drill bit surfaced. Increasing the entry angle of the second hole to approximately 15º, the drill bit surfaced well over 100 feet from the entrance. On the third and final test the entry angle was increased to 30º. Joint after joint was fed into the hole. Tension was high when finally the bit surfaced nearly 300 feet away and 40 feet offline from the planned bore path. Cherrington was both relieved and elated that the discarded drilling tools he had rescued from the scrap pile actually performed as expected. The tests confirmed that given the optimum entry angle, proper drilling techniques and the right downhole tool assembly a barrier such as a river could be crossed using horizontal drilling techniques. Horizontal drilling would be a revolutionary step to eliminate all the problems typically associated with conventional trenching methods. With confidence that his technique would work, Cherrington packed up and headed home to make plans to drill under the Pajaro River.

Convinced now that it was possible to traverse the Pajaro River using Horizontal Drilling techniques, the two-vertical caisson scheme was abandoned. Before starting the job, however, Cherrington decided to investigate available oil field directional drilling technology and methods that might be adapted to horizontal drilling. After learning what was available, he decided to change his original drilling plan to incorporate oil field tools and drilling practices that might increase his chance of success. This would be the first attempt to directionally drill, surface to surface, under a river using directional drilling tools.

Cherrington used a 5" OD mud motor with a bent sub above and a single shot survey system. The single shot device, while crude compared today’s downhole electronic survey instrumentation, would provide a reasonably accurate measurement of azimuth, inclination and tool-face readings of the bottom hole assembly while drilling. A single shot survey tool consisted of a gimbaled, free-floating compass incorporating a concave glass hemisphere scribed with azimuth and inclination lines. Housed in a

First HDD rig
1-3/8" OD, non-magnetic cylinder and liquid filled, the force of gravity on a small ball rolling in the glass hemisphere indicated the direction of the bottom hole assembly relative to magnetic north and its inclination relative to the vertical. The tool was pumped down the drill pipe and docked in a locating receptacle just behind the bent sub and mud motor. Once the tool was in position, a miniature camera with light and a timer attached took a picture of the compass and ball at a pre-set time.

The single shot was then retrieved to the surface via an attached wire line and the film was developed. The reading, or survey provided azimuth, inclination and tool face (a measurement of the direction that the bent-sub is pointing about the axis of the borehole relative to the high side of the hole).

Using the oilfield directional drilling tools proved disappointing, however. Hole angle could not be sufficiently built nor even maintained, so the approach was quickly abandoned in favor of more familiar utility boring techniques. Reverting to the lessons learned while drilling adjacent to the Feather River, Cherrington successfully crossed the Pajaro River using the discarded drilling tools that tended to drill back to the surface. It is interesting to look back on that experience today. Titan Contractors was a fledgling company trying to change the way the world did things. Experimenting with new technology was not necessarily without risk. Most customers were not willing to allow their projects to be used for proving new ideas or technology. Fortunately, PG&E’s R&D department funded the Pajaro River project that made it possible for Cherrington to prove his concept and introduce Horizontal Directional Drilling, HDD, to the world.

Since that first HDD crossing, Martin Cherrington has dedicated his life to pushing the limits of the HDD technology envelope. He holds numerous patents that have significantly advanced the industry and made what once was thought impossible a reality. Who would have thought, in 1971, while standing on the banks of the Pajaro River that one day pipelines and conduits would be routinely placed under rivers the size of the Mississippi, that outfall and beach approaches would be possible to bring deep sea telecommunications onshore, all with minimum impact to the environment.

For more info. visit www.cherrington.com