DIRECTIONAL DRILLING
Sigra personnel have a substantial background in directional drilling from a variety of viewpoints. These include the theoretical analysis of torque and drag models, the development of directional drilling equipment and the practical maintenance of directional drilling equipment. This experience covers directional drilling for civil engineering purposes, coal seam methane and hard rock applications. The paper "Directional Drilling - The Growth Area" was presented at International Drill '99.
top
Field Services
At the present moment Sigra offer no field services for directional drilling.
top
Consulting
Sigra can provide consulting expertise in designing directional hole trajectories to minimise drilling problems. This consulting assistance is based on sound practical knowledge supported by Sigra's software. This software comprises a drilling fluid model and a stiff torque and drag model. The original origins of this software is described in the ACARP report "Optimisation of Long Hole Drilling Equipment" (available in compressed MS Word [75kb], compressed WordPerfect [61kb] or pdf format [399kb]).
Given information on the borehole size, drill string and hole trajectory Sigra can model the fluid flow behaviour in the hole. One of the purposes of modelling is to ensure that turbulent flow in sloping and near horizontal holes is maintained. This is required to ensure cuttings are lifted. The model also provides a basis for examining in hole pressures from the viewpoints of blowout control and formation damage.
The stiff torque and drag model can be used to predict the loadings and hence stresses in every section of a drill string. Given Sigra's knowledge of drill string connection behaviour (see ACARP report C4049) rod loading can be interpreted in terms of safe drilling practices that will not lead to drill rod breakage or getting stuck in hole.
The software may be used either as a predictive tool prior to drilling or as a check during drilling. The real hole trajectory may be more tortuous than that predicted and this may have a dramatic effect on friction. Regular measurements of torque, thrust and pullback load are vital information that may be used as input for the model.
In addition to the drilling models described Sigra has a finite element model of a drill string that can be used to design stabilizers or collars. This is normally used to arrive at the design of bottom hole assemblies that will drill a straight hole.
top
Equipment
Sigra has developed three measurement while drilling systems. The first is a record-on-board rotary tool. The second is a geosteering tool which transmits information to surface whilst the third is a drill rig monitoring system. It has also built a directional hammer for drilling in hard rock.
Rotary Tool
The rotary tool is a record-on-board tool that is designed to operate with rotary drilling. The tool is a combination survey tool and torque and thrust sensor. It is designed to record processed torque, thrust and rotation speed information on board every quarter second. When rotation ceases the measurement of torque and thrust ceases and a survey of inclination, azimuth and tool face angle is made utilizing the tool's on board triaxial magnetometers and accelerometers. The tool then lies dormant until rotation recommences whereupon it restarts recording torque, thrust and rotation speed. At the completion of drilling the drill rods are pulled and information stored in the tool is downloaded into a computer.
To utilize this information it is necessary to maintain a record of the penetration of the drill with time. This can be either undertaken manually or more usefully through the use of an automatic drill rig monitor.
When used in combination with penetration rate data the torque and thrust data downloaded from the tool provides signatures for the rock type and structures which are encountered by the bit. The tool is used most advantageously behind a drag bit where the cutting signature is most clear. The best kind of drag bit to use with the tool is manufactured with poly-crystalline diamond cutters as these tend to self sharpen and therefore the signal is not degraded by the drill bit becoming blunt.
Experimental evidence shows that the information from the tool can be readily used to distinguish between coal types and different sedimentary rocks. The drilling trace information is also particularly useful for the detection of structure. As such it is potentially the most useful tool in existence for detecting outburst prone structures in coal seams. Research remains to relate all the various drilling signatures to rock types.
The present tool is N size (76 mm diameter) and could be used behind an 89 to 96 mm PCD drill bit. It would be possible to build smaller tools down to B size (62 mm diameter) as well as bigger tools.
The value of such a tool is that it can deliver information on hole direction and trajectory as part of a normal rotary drilling operation and without needing drilling personnel skilled in the use of electronics.
The use of properly designed stabilizers to ensure a straight hole makes rotary drilling attractive. This design can be achieved as described in the section on consulting.
top
Geosteering Tool
Sigra has developed a geosteering tool with the assistance of the Australian Coal Association Research Program and an Australian Federal Government Start Grant. This tool has been built for in-seam directional drilling in coal seams. Its use is however not necessarily restricted to this purpose.
The tool comprises a survey module based on Sigra's own triaxial magnetometers and accelerometers. This is highly accurate (0.15 degree in all directions) and very shock proof. A torque and thrust sensor is located ahead of the survey tool and behind it is located a resistivity tool.
Information from the drill is transmitted up the drill string electronically to a computer located at the drill collar. The communications is achieved by fitting the drill rods with an insulated conductor rod. When the rods are made up the conductor rods plug into each other via a waterproof connector. Communication is by a pulsed digital current loop via the conductor and the drill string.
This system is shown conceptually in drawing D14 and the assembly in D15. It is currently available for N sized drill rods.
top
Drill Rig Monitor
Sigra can fit most drilling rigs with a drill rig monitor based upon Sigra's field data logger. Inputs to this are head displacement, thrust, pullback, rotation speed, drilling fluid pressure, flow rate and in some cases, depending on the type of drill rig, torque.
top
Directional Hammer
Sigra has built and are continuing to develop a directional hammer. This is shown in photographs P11 and P12. Partners to further this project are sought.
top
Research and Development
All of the software and hardware described above has been developed and built in-house. This work represents a substantial research and development effort and capability. Sigra continue to develop and upgrade in-house equipment, software and expertise all the time. Sigra will also consider undertaking research and development for third parties.