Question answered by Charles Stockton, Managing Director of Stockton Drilling Services.
HDD expert Charles Stockton says:
Firstly, drilling risks should always be minimised by undertaking adequate geotechnical surveys prior to drilling commencing. The contractor then needs to maintain thorough drilling records, which can be used to continually refine the geological model and assist in decision making during construction. Too often geotechnical information is limited and specific geological surveys have not been conducted along the entire HDD route. If the geotechnical conditions are known prior to drilling, the identified risks can be minimised through proactive planning and management rather than being solved reactively on site.
Contractors or experienced consultants should work with the client to develop an appropriate scope of work for the survey, as Stockton Drilling are currently doing for Arrow Energy in Queensland. Regardless of how comprehensive the site geotechnical surveys for the drilling program are, it is also essential to maintain thorough site records. These records should be used to continually refine the geological model, assist in site decision making and plan for future projects.
Often I hear contractors complain that there isn’t sufficient or appropriate reference material available to help them plan complex crossings. I advise them that the best information available to them is their own drilling records. It is essential for contractors to keep accurate drilling logs for all projects completed. These drilling logs, once analysed, then provide the competitive edge and become the basis for planning and costing future projects. The drilling logs must accurately capture details of the tooling, rig performance and drilling fluid system.
These records can then be aligned with the steering engineers report, allowing for a precise geological model, including timeline plots to be constructed for use in the reaming operations. The timeline plots minutes per drill pipe by distance, clearly indicating the different reaming stages and formation changes making it a useful planning tool.
Often, the need for detailed data collection and mapping of each metre of the hole as it is drilled is overlooked, instead relying heavily on existing borehole data. Often these records would only be referred to if a problem occurs later on, which is a reactive rather than proactive approach. A combination of drillers logs, mud logs and steering logs should be used to build up a detailed geological model in real time.
Drawing timeline plots can also provide a means to:
•Compare tooling performance and refine cutter and tool selection
•Plan when trips will be conducted for cleaning or cutter change
•Determine the mud program and pump rates for each section of the hole
•Note any formation changes to prevent doglegs or twist offs during reaming
•Plan expected durations for each phase of the work
•Formalise information to be fed back into the estimating and planning departments
•Optimise decision making for schedule planning and equipment sparing.
The scale at which data is monitored and analysed must also be considered. Every metre or every minute may be too fine and only produce conflicting information; while every hour or 50m may be too coarse and not provide discernable differences. It may also be necessary to monitor different parts of the operations at different intervals. As long as the data is recorded regularly and diligently then it will always be possible to refine your search to highlight the areas of concern.
Another example of why precise record keeping is essential is during recovery of a broken drill pipe. When forward reaming, the drill pipe is put under compression rather than tension. Therefore the chances for drill pipe failure are substantially higher than with conventional back reaming. It is again essential that precise measurements are taken of everything that goes down hole so if something goes wrong the diameter and location of the broken component are known. Both internal and external diameters, the distance to the next upset or tool joint and the precise length and diameter of all components crossover and subs must be known. With this information available it should be possible for the team to determine the best fishing tool to be employed and carefully orchestrate recovery of the broken component.
Developing a culture within the industry where ideas are shared will help to promote HDD as a reliable and robust solution to the majority of today’s pipeline problems. The industry will continue to grow and not be surpassed by demand for new technologies as long as we continue to meet the client’s expectations.