Drilling advances

	Vol. 226 No. 0
LES SKINNER, PE CONTRIBUTING EDITOR

 Drilling advances

 LES SKINNER, PE CONTRIBUTING EDITOR lskinner@cudd.com

Drilling research through DOE initiative. The US Department of Energy has announced several research projects aimed at making significant improvements in the recovery of oil and gas and improving the environment. Several of these have the potential for synergistic benefits while others are stand-alone projects.

The list is long and varied. It includes projects to improve subsurface definition and provide comprehensive subsurface studies in three depositional systems. Others deal with improved characterization and advanced recovery techniques from existing oil and gas reservoirs. Another project is intended to detect pipeline leaks from high-altitude, unmanned aerial vehicles. 

One significant initiative involves sequestering carbon dioxide in non-productive Frio sands along the Gulf Coast. Already, the first volume of CO₂ has been injected, some 1,600 tons of the stuff, and now the second phase of the project is in progress – finding out where it went. Others in the industry are looking toward CO₂ injection in coalbed methane projects, with the goal of simultaneously improving hydrocarbon gas recovery while sequestering the CO₂ through absorption on the coal’s face. 

Some of these research initiatives involve drilling. Two are intended to develop ultra-high speed downhole motors to provide bit rotary speeds well above those available using current technology through positive-displacement motors or turbines. APS Technology, Inc. is to design and test a gearing system for use with these conventional motors that will allow a bit to rotate up to 10,000 rpm. Impact Technologies and the University of Missouri at Rolla are investigating high-speed electric motors to provide this capability. This high-speed capability is to be coupled with bits capable of drilling at these high rotary speeds. 

The DOE is also sponsoring six research projects into microhole drilling. In this type of drilling, the borehole size is reduced considerably. For example, an 8-1/2-in. hole could be reduced to as little as 3-1/2-in. with associated reductions in mud system volumes, casing sizes, cement volumes and virtually every other portion of the drilling plan including the rig. Coiled tubing drilling (CTD) technology should be advanced both by the microhole drilling technology and high rotary speed motors and bits. Articles on this DOE effort appeared in World Oil’s February and December issues. 

While these research projects are fascinating, the subsequent research that is bound to follow should be at least as captivating if not more so. For example, what mud system is required for an ultra-high speed drilling system. Presumably, scraper-type bits will be needed since it is doubtful that any coned drill bit – whether tooth, button or disc – would have the bearing surface area and lubrication system necessary to spin at 10,000 rpm for very long.

It follows that drill cuttings from an improved PDC or other scraper-type bit would be very, very fine (roughly the consistency of foot powder). The best parallel is a high-speed dentist’s drill – the tooth cuttings are so fine they appear to be a vapor plume instead of solid particles. 

Circulating these cuttings out of the hole should be simple. Low slip velocities would allow viscosity reduction and thixotropic requirements for drilling fluids.

Solid/ fluid separation may become problematic with such fine cuttings. Specialized equipment and procedures to provide fresh, clean fluids may need to be developed. 

The mud logger is likely to have a difficult time identifying lithology and fossils with such small size cuttings. Will a small electron microscope be required in the field to find and identify tiny pieces of micro-fossils? 

Well control techniques will probably need to be revisited, where high penetration rates make it likely that the entire zone will be drilled through before a kick can be identified. An emerging problem today involves early kick detection where fast penetration rates exist. In a small-diameter hole, where the annular volume is limited, kick identification, rapid shut-in, and kick circulation may only require a few minutes.

Directional tools and controls may require upgrading through research. Accurate azimuth and deviation angle detection must be available quickly. Once the bit starts drifting off the intended path, a dogleg will probably develop rapidly. If CTD is employed, the currently available resources for changing hole direction are limited. Rotary steerable systems will probably be needed for microhole high-speed CTD using some type of yet undeveloped device.

High-speed electric motors require some type of conductor to provide current to the downhole driver. This conductor will probably provide the means for monitoring the BHA including the motor, bit, MWD, LWD, PWD and other systems. If conventional mud motors are used with an improved gearing system to provide the high rotary speeds, can the BHA and instrumentation package be monitored using conventional pulsers or electromagnetic data transmission? If not, perhaps the DOE’s research initiative into development of ground-penetrating radar to monitor drilling progress and downhole tools will provide the means for doing so. 

New, improved drill string connections may also be needed. A rotary tool imparting energy to the rock face, turning at any speed, transfers left-hand torque to the drill string above it. Will a bit turning at 10,000 rpm that encounters a tight spot simply unscrew itself when it turns loose? If so, a splined connection or some type of locking mechanism will be required to avoid leaving a fish in the hole.

One cannot help but think that fishing in a microhole is akin to submitting to some type of sadistic physical torture or perhaps a root canal. Fishing one of these high-cost bits out of a small-diameter hole must be avoided. So, research to develop specialized connections for high-speed microhole drilling is imperative.

These new developments will doubtlessly be valuable for other types of drilling operations. The trickle-down effect may be more significant for other drilling operations than for high-speed microhole drilling. The prospects for extending the results of these research programs to other areas in the drilling industry are no less fascinating or exciting. We wish those involved the best of luck. 

Les Skinner, VP and Division Manager for Energy Personnel International, Houston, and a chemical engineering graduate from Texas Tech University, has 32 years’ experience in drilling and well control with major/ independent operators and well-control companies.