Wireline bias hard to foil

March 20, 2006
High rig day rates, slack time-cutting campaign signals MWD-LWD acceptance, uptake, says Sperry; new technology looms ahead, too

High rig day rates, slack time-cutting campaign signals MWD-LWD acceptance, uptake, says Sperry; new technology looms ahead, too

There’s no doubt operators everywhere are using MWD-LWD services more these days than ever before. The reason is that much improved, real-time data from measurement/logging while-drilling tools are consistent with other down-hole tool advances in helping keep the drill string in the hole, drilling for longer periods. This translates into lower risk to drilling dynamics and significant reductions in costly non-productive rig time.

Ron Dirksen, global M/LWD manager in Halliburton; Sperry Drilling Services’ drilling and formation evaluation division, puts it this way:

“Rig day rates are sky-high everywhere today” he said. “Not so long ago, the choice between MWD-LWD and wireline applications was purely a financial one, wireline being the less expensive option. That’s not the case anymore. With while-drilling services, customers get detailed, real-time feedback instantaneously, instead of having to pull the drill string to make logging runs with straight wireline or pipe-conveyed wireline tools.”

Other obvious MWD-LWD advantages, said Dirksen, include better data acquisition before inevitable drilling fluid effects materialize at the borehole wall-an important consideration in high-cost drilling environments such as offshore and in ever-longer horizontal well sections.

“There is far less invasion and subsequent hole deterioration,” he said. “As part of the bottom-hole assembly (BHA), MWD-LWD tools operate near the bit as the well is being drilled. With other options, including wireline, wellbore stability issues can arise after the drill string is pulled from the hole and before the wireline tools are run into the hole to take their measurements. In that case, not only does the operator face the added cost of rig slack time, but his ability to get a ‘true,’ or near real-time measurement of down-hole conditions is, at times, compromised.”

Dirksen also noted that even in the recent past, smaller producing companies and national oil companies did not often choose the MWD-LWD option-but not necessarily because of the cost. There are differences that aren’t readily apparent, he added.

“Older, more experienced engineers and geoscientists grew up with wireline technology,” he observed. “We are also seeing that many of the industry’s newer hires studied wireline technology in university because MWD-LWD data was not generally available. The upshot is, they tend to want to look at wireline data also. It’s understandable. But it’s up to us in the while-drilling domain to further educate them about MWD-LWD technology and its advances. Fortunately, the data quality and the significant cuts in unproductive rig time are compelling evidence, so operators of all sizes are converting pretty fast.”

WD formation pressure tests bode well

While the benefits from MWD-LWD are numerous, perhaps one of the most persuasive arguments for while-drilling technology lies in the effectiveness of formation pressure testing while drilling, said Dirksen. It was a service first introduced by Sperry and was followed with similar tools from competitors. Almost universally such LWD tools deliver data quality equal to or greater than straight wireline and drill pipe-conveyed wireline testers, he said, which for years were deemed the most reliable technologies for gauging formation pore pressures.

Since it was introduced in 2003, Sperry’s GeoTap® LWD tester, with tools available for hole sizes ranging from 5¾ inches D. to 18 inches D, has exceeded expectations, said Dirksen.

The Sperry tester underwent extensive worldwide field trials before being commercialized, performing successfully in a variety of lithologies at depths greater than 29,000 feet and in deviations of up to 104 degrees inclination, both with and without mud circulation, Dirksen said. Since that time, numerous case histories attest to the tool’s effectiveness.

The GeoTap tester obtains direct pore pressure measurements in 7-10 minutes using a wireline-type probe and pad and a precision quartz pressure sensor. With it, numerous tests can be made in a single drilling run, Dirksen said, with accuracy ranging to within 1% of comparable wireline data.

The tool can be controlled from the surface with the company’s Geo-Span® real-time, bi-directional downlink drilling control system, he said. That allows operators to make on-the-fly decisions about testing while simultaneously sending other drilling and reservoir data up hole. Recent applications of the GeoTap/Geo-Span, coupled with the company’s Geo-Pilot® rotary steerable system, have delivered multiple formation pressure test data successfully in the North Sea, the Gulf of Mexico, as well as many other countries, he noted.

Most recently-late last year-a slim-hole (4¾-inch) rotary steerable BHA, including a GeoTap, was deployed in a 6½-inch hole section of a deep Gulf of Mexico well, said Dirksen. The package also included a quad combo (induction, litho-density, compensated neutron, sonic) LWD suite with vibration sensors. All 11 pressure tests were successful, said Dirksen.

“It was the first time pressures were taken with a 4¾-inch LWD formation pressure tester,” he remarked. “It also demonstrated the ability to eliminate the need for other logging technology. But it also saves rig time and reduces the potential risk of losing the borehole.”

Geosteering WD growing rapidly

With increased business come better revenue streams for service companies, Dirksen noted. That allows more research and development (R&D) spending for both new and enhanced MWD-LWD technology.

“The need to characterize reservoirs more accurately is an increasing trend in R&D,” he said, “as well as developing software and instruments to better place the wellbore in the reservoir, particularly for re-entry drilling.”

In Sperry’s case, better wellbore placement is being achieved with the new StrataSteer® 3-D geosteering service, said Dirksen. It is composed of the company’s Stellar® MWD-LWD suite of sensors that capture critical real-time data, advanced geosteering software that integrates the data with a surface geological model, steerable drilling tools to position and control wellbore trajectory, and a specialist trained to interpret the data to steer the well.

With such 3-D steering software, said Dirksen, it’s possible to interpret MWD-LWD and rotary steerable tool data to correctly land the well in the reservoir, optimize the well path by avoiding undesired bed boundaries or fluid contacts, analyze reservoir properties, interpret geological borehole images, and maximize the productive interval.

Crucial to optimal use of such geosteering/wellbore placement technology is real-time communications among the various drilling disciplines and their respective personnel, said Dirksen, and their ability to interpret the geological situation to make accurate, real-time steering decisions.

“Geologists, geophysicists, petrophysicists, drilling engineers, directional drillers and LWD specialists can all contribute to a successful geosteering operation,” he said. “But it’s sometimes not practical to have all these people available at the well site. That’s where INSITE® comes in.”

The INSITE service is Halliburton’s data acquisition, display and interpretation system, he said. Through it, the well site database can be replicated to real-time operations centers (RTOCs) located in customers’ offices or elsewhere. This allows an entire asset team-at the well site and at the office-to make informed, collaborative decisions, with 24-hour access to data view from any computer connected to the Internet. With the INSITE service, a well can be geosteered from any location, even if it’s thousands of miles away, he said.

Wired pipe expands telemetry options

While Sperry MWD-LWD systems use mud-pulse and EM telemetry to transmit data to and from the well, Dirksen said the potential for faster telemetry from newly developed wired drill pipe can be utilized with addition of interface subs.

“The main thing for us is to make sure our customers get their data,” he observed. “There is the possibility that we would take advantage of that technology in cases where wired pipe is used. In other cases, we might consider it supplemental in nature, using mud pulse for some tools and wired pipe telemetry for others. But that probably won’t be determined for at least a year or two.”

Since the 1980s, when a predecessor company invented wireline-conveyed logging using magnetic resonance imaging, Sperry continues to be a leader in that arena, Dirksen said. The company subsequently commercialized the industry’s first magnetic resonance imaging-based logging-while-drilling (MRIL-WD) tool in 2001, he added.

Magnetic resonance imaging logs provide total fluid-filled porosity in the LWD mode, as well as free fluid, capillary bound and clay bound water indices. For deviated well sections, the service provides hydrocarbon typing and permeability estimates in the while-sliding, evaluation logging mode.

Also, the MRIL-WD tool can provide a measure of rock porosity that’s lithology independent, making a radioactive source unnecessary, he said.

The next step is to combine magnetic resonance imaging technology with formation pressure test while-drilling technology for better formation fluid identification, he said.

Finally, Dirksen noted that current industry R&D efforts are being aimed at significant advances and refinements in the sophistication of MWD-LWD technology, with particular emphasis on new sensor iterations.

“And the advances will be in all sensors, not just the relatively few that are compatible with those in wireline technology,” he remarked. “All MWD-LWD sensors will eventually equal or be better than those associated with wireline technology, and while-drilling systems ultimately will dominate the drilling environment.”