Team work

Weatherford and Chevron teamed up to develop a LWD service capable of running in high temperature environments, such as the Gulf of Thailand. Jerry Lee reports on how the project came together.

Technician examines HEX electronics in Songkhla. Photos from Weatherford.

Logging-while-drilling (LWD) tools are robust and built to withstand the stresses of oilfield conditions, but even they can succumb to the demands of high temperature environments. Operations can become challenging, making data acquisition difficult. Dealing with such a situation, Chevron Thailand partnered with Weatherford to develop a LWD tool capable of running in high-temperature environments, to reduce non-productive time (NPT).

In the Gulf of Thailand, an area which sees some of the world’s highest bottom hole temperatures, standard LWD tools are typically not up to the challenge; with temperatures reaching over 200°C (or as high as 3.2°F/100ft), standard LWD tools are only rated to 175°C. Lacking a hardier tool, drillers adapted by using temperature mitigation techniques; e.g. stop drilling, pull up to a cooler zone, and circulate mud to cool the tool. This mitigation process works well enough as a short-term solution, however, it must be done each time the tool needs cooling. If the process does not work, the tool will likely fail and will need replacement; in both cases, NPT and high rig costs will accumulate.

Chevron Thailand was familiar with LWD-related NPT, however, the operator still needed to drill safely and has a specific requirement to eliminate or minimize wireline logging in all wells.

“For our operation, we want to drill at maximum speed without any interruptions,” says Douglas Ellis, drilling engineer and joint development project manager, Chevron Thailand Exploration and Production. “Logging the well and taking surveys needs to be done concurrently with the normal routine drilling operation to maximize efficiency.

“In addition, the directional driller uses the survey data to calculate and make adjustments to the well trajectory and the earth scientists use the petrophysical data to determine the rock and reservoir properties. All of this is done during the drilling operation,” he says.

With NPT costs mounting, Chevron knew it needed a better solution: a triple combo high-temperature LWD (HT LWD) tool capable of acquiring porosity, density, and resistivity data. This fell in line with Chevron’s capital efficiency strategy and the Offline Data Acquisition Project, the aim of which is to develop concepts and technologies to optimize rig-time; e.g. acquiring the petrophysical and reservoir data while drilling. As a result, Chevron asked Weatherford to accelerate the development of HT LWD tools.

Weatherford dedicated its research and development resources to fast track the development of 200°C capable tools, with Chevron investing US$1.575 million for development cost.

Feeling the heat

HEX Tools ready for deployment in Thailand.

For phase 1 of Weatherford’s proposal, prototypes were developed utilizing high-temperature mud pulse telemetry, directional sensors, as well as neutron porosity, gamma ray, and pressure-while-drilling logging tools.

At fields with temperatures exceeding 175°C, the electronics in standard LWD tools start to break down and fail. For areas like the Gulf of Thailand, electronic components that can survive in these temperatures long enough to get the logging job done are needed.

“We completely redesigned the electronics packages within the tool to withstand 200 hours of operation in 200˚C and four hours of survival in 210˚C,” says Richard Barton, product champion – new technologies, Weatherford. “At 210˚C the tools are designed to shut down and preserve themselves so they can be tripped out of hole and reused again.”

The HeatWave Extreme LWD service leverages technologies used in Weatherford’s HEL system but improves the temperature rating. The new service also includes optional bore and annular pressure as well as gamma and neutron porosity measurements.

Innovation in electronics was required for the tool to work at these high temperatures. “The biggest hurdles, and time cost, in the development part of the project was the selection of the electronic components that could operate at that temperature,” Barton says. “We took components off the shelf, heated them up, and they failed. We had to use different components organized in different ways to find a solution, and each time we had to rewrite the firmware to use those components. Then, we designed a completely new PCB (printed circuit board), populated the PCB with the selected components, and qualified them at 200°C for 200 hours and 210°C for four hours.”

In addition to the PCB and components, the HT-LWD tool required new elastomer seals and a new type of battery insert that has the ability to function at high temperatures.

With the ability to operate at high temperatures, engineers can focus on drilling, logging, and working towards optimizing the cost of the well. Mitigation tactics to cool the tool are avoided, as well as the need to trip in and out to replace the tool if it fails.

“If you stop temperature mitigation procedures then you could be saving up to 11 hours per well,” Barton says. “And if you prevent one trip per well, then you’re saving at least 12-15 hours of rig time.”

Case study

Winners of the 2015 Thailand SPE E&P Award. [Left to right] Steve McBride, Weatherford Country Manager, and Doug Ellis, Senior Drilling Engineer, Chevron Thailand.

Five HT-LWD prototypes were completed and qualified and then taken to the Gulf of Thailand in January 2015 for field testing. The HeatWave Extreme (HEX) project, as it was called, involved utilizing the HT LWD tools (HEX tools) for a 22-well campaign. During this campaign, Chevron experienced zero tool failures, blind runs, safety incidents, or NPT in 25 runs and 1218 hours of drilling. Without having to perform cooling trips, Chevron saved around 223 hours of rig time and decreased the average time to drill and log the well to 6.2 days per well.

To date, 27 wells and 186,250ft (56,769m) have been drilled, with no failures or service interruptions in 2175 operating hours. The HEX tools also set multiple drilling records for Chevron Thailand: deepest 3-string production well: 11,566ft TVD; first well greater than 10,500ft TVD drilled in less than four days: 10,552ft TVD in 3.88 days; fastest well deeper than 11,000ft TVD: 11,316ft TVD in 5.31 days.

The HEX tools experienced extreme temperatures, including a maximum circulating temperature while drilling of 198°C, and recorded a maximum temperature of 213°C. During the 213°C run, the tool was run to bottom however circulation was not initiated until it was near the bottom and transmitted a temperature reading of 212°C. All of the sensors and batteries were operational except for the neutron sensor, which had thermally shut-down at 212°C. After being cooled, the neutron sensor functioned normally.

“This is something that’s unprecedented,” Ellis says. “Normally, we would never see wellbore temperatures that high and circulation would be initiated occasionally while running in the hole. I doubt this will ever happen again in our operation.”

As a result of their success, the HeatWave Extreme project won the 2015 SPE E&P award on 26 Feb 2016 in Bangkok, Thailand.

“This was Chevron Thailand’s first joint development project, and Weatherford’s R&D did an awesome job designing, testing and building the tools,” Ellis says. “Winning the award would not have been possible without the operational team in the office and on the rig. It was the personnel in the field that pushed the tools to the absolute limit and proved the reliability of the tools.”

Next phase

Despite the success of the HEX tool, Weatherford is not yet finished with the project.

“At the moment we’ve completed phase 1 of the project with Chevron,” Barton says. “Phase 2, we’re going to be developing resistivity and density measurements to go along with it as well.”

Phase 2, endorsed by Chevron in January 2015, will complete the suite of high temperature triple combo tools.

“The big savings will come when the HT triple combo tools are deployed,” Ellis says. “These tools can be run on all wells with the potential to exceed 175°C without the downside of having to spend time running wireline logs. One question that I have always been asked [by operations personnel] during the field trials was, ‘when will the HT triple-combo tools be here?’ My answer is Q3 2016.”