Sept. 1, 2000
The subject is widely discussed around the industry: if we could drill with lasers, all of our problems would be solved.

En-"light"-ened drilling

The subject is widely discussed around the industry: if we could drill with lasers, all of our problems would be solved. No more worrying about bit wear, junk in the hole, and everyone would be happy with exceptional rates of penetration. This was usually followed by collective laugh and never mentioned again. Well, that laugh may have just changed into a raised eyebrow of interest.

Researchers at Reading University in southern England have developed a laser beam technology, used to detect the presence of gas bubbles in a fluid column. Tested in the laboratory using water droplets in a fluid medium, success has been achieved measuring the size, speed, and optical properties of the water drops.

Basicly, the detection and measurement technique illuminates the fluid column around the drill bit with sheets of laser light. As fluid bubbles pass through these laser sheets, they reflect light similar to dust particles passing through a movie projector beam. Bubble size and speed moving through the annulus can be ascertained. The technique takes the simple measurement of bubbles in the fluid string to a higher level and actually measures the amount of light bending as it passes through the bubble. The degree of bending depends on the bubbles' optical properties giving the ability to distinguish rock cuttings from actual fluid components.

Although this is not actually drilling with a laser, the drilling process can be more effectively monitored via this measurement system, and is just one step closer to an actual laser drilling system. Other light energy-related measurement techniques used currently in the oil and gas industry include fiber-optic pressure and temperature monitoring markets, such as the Ghost tool from Schlumberger, the LaserStrat system from Sperry Sun Drilling Services, and Chemo-Strat developed in the UK. Fiber-optical measurement of temperature and pressure are not necessarily new, but a key component in the future of intelligent wells.

  • The Ghost tool from Schlumberger uses a light source and the optical properties of fluids to determine multiphase flow component percentages. Component percentage and relative flow rate of the multi-phase components can be determined.
  • The LaserStrat system from Sperry Sun Drilling Services and Chemo-Strat in the UK, uses laser technology for spectral element analysis of rock cutting samples. Stratigraphic characterization of the reservoir is then made possible in the absence of paleontological information.

As you can see, light energy technologies are playing a greater role in the upstream oil and gas industry - steps leading to, shall we say, a complete laser-optical drilling and well monitoring system."

HP/HT operations heating up

Deeper wells imply higher temperatures. Higher temperatures demand that top priority be placed on qualified electronics for operating in the tougher environments. A year ago, 200

For short periods of operation, these upper limits are achievable, but the jury is still out on what detrimental effects these short periods have on the total life expectancy of a given electronics assembly. In fact, industry-wide experience has shown that consecutive runs with the same assembly into these "upper-limit" environments may result in premature failures. The dominant industry-wide opinion is that there is no predicting what long-term effects will result after a tool has been exposed to "upper-limit" environments.

Reports of "strange" tool behavior (not necessarily hard component failures) are common with tools that have previously operated in an "upper-limit" environment. To minimize the potential of reoccurrence, and new problems, it is common practice to go above and beyond normal repair and maintenance service guidelines and replace all critical components - driving operating costs higher.

Wireline conveyed tools are more easily adapted to harsh environments. Heat dissipation can be improved via electrical and tool design methods. While-drilling tools, however, suffer more from the inability to dissipate heat, plus they generate a lot more heat than their wireline counterparts. While-drilling tools demand ruggedized electrical components. A lot of these components are the same as the wireline tools, but slightly re-designed and re-configured inside the assembly to minimize vibration and temperature effects.

Flexibility of tool design and configuration seems to be a strong asset when dealing with HP/HT electronics. Being able to replace failed and fatigued components easily, yields an advantage in adapting to HP/HT environments. As an example, a project in the North Sea recently required refurbishing and upgrading of existing tools to fit that project's specific HP/HT downhole environment. Flexibility of design and good planning resulted in record runs for one service company and operator.

Wireline HP/HT success

A deep North Sea Triassic well was logged with slim high-temperature tools earlier this year. The logging program was designed to evaluate Elf Exploration UK PLC - Franklin Field's Triassic section, which had never before been drilled or explored. The 5 5/8-in. hole was drilled to 20,408 ft at 23 degrees deviation, with 18.4 lb/bbl oil base mud. The geologic section was characterized by hard, low-porosity sediments, with downhole conditions reaching 204 degrees C and 19,000 psi pressure.

During the HP/HT logging runs, the Xtreme platform (being run for the first time in a 5 5/8 in. setting) from Schlumberger collected caliper, array induction, sonic, gamma ray, density, and epithermal porosity data. A high-temperature version of the SRFT* (Slim Repeat Formation Tester) tool was modified in Aberdeen to accommodate a second pressure gauge, a sapphire gauge in memory mode, to ensure that pressure data could be obtained during conditions exceeding the temperature limits of the tool's standard crystal quartz gauge.

This modified tool could withstand temperatures up to 221

All runs into this "upper-limit" environment were made successfully with no failures, and based on initial logging results, Elf decided to deepen the well and conduct further logging using the MDT* modular formation testing tool and a hostile OBDT* oil-based dipmeter string - also firsts, in a 5 5/8-in. well.

The formation testing tool's dynamic features were manipulated to confirm pressures and gradients in extremely tight formations.

Industry, electronics at odds on components

In the world of installed systems, like intelligent wells and well monitoring systems, extended time in the "upper-limit" environment is requ-ired. Expro (Aberdeen) has proposed a minimum standard of 5-years sustained exposure at 200

The limiting factor will be the availability of qualified, vendor-supplied components, which is where most of the effort will be focused. Working against these efforts is the electronics industry, which is adopting lower cost-effective standards set forth in the customer-off-the-shelf (COTS) policy already implemented by the US government.