Operators in the Gulf of Thailand engage in fast-paced drilling operations, striving to produce sufficient volumes of natural gas to support the needs of Asia’s growing economies. As an example, an operator plans to drill about 500 gas wells over the next three years. The key technical challenge is that nearly half of these wells will penetrate reservoirs with bottomhole circulating temperatures above 175 C (350 F). That, as it turns out, is the operational limit of most of the existing commercial HP/HT rotary steerable systems (RSS) and of Schlumberger’s MWD tools.

When downhole electronics, seals and sensors are exposed to high temperatures, tool failures increase as their life expectancy plummets, causing increased nonproductive time (NPT) for operators. Reliability begins to suffer when temperatures exceed 150 C (302 F). Components designed to last about 1,000 hours at 150 C survive less than 100 hours at 175 C. Therefore, when temperatures reach 175 C, drillers in the Gulf of Thailand and other HP/HT regimes typically halt operations, pull the MWD and/or RSS tools out of the hole and continue drilling blind. They rely on conventional stabilized or packed bottomhole assemblies (BHAs) without any real-time measurements or directional control. After each hole section, they must pull out of hole again and run a separate gyroscopic survey to confirm well positioning.

This common approach takes longer than drilling under normal conditions. Additional trips incur NPT. Without downhole measurements to steer the borehole, risks and costs associated with well control and collision increase. It is possible, in some cases, to miss the target completely, resulting in lost production or potentially a dry well.

The following case study with recent advancements in MWD and RSS technology demonstrates how operators in the Gulf of Thailand—and elsewhere— are enabled to continue drilling safely, efficiently and confidently, even under very high temperatures and pressures.

Gulf of Thailand case study

One E&P company in the Gulf of Thailand plans to drill up to 75 exploration and development wells per year for the next three years in temperatures above 175 C. To reduce the cost of well construction and the uncertainty of inaccurate wellbore placement while drilling blindly, the operator decided to field-test a new HP/HT MWD tool. The top objective for its first test well was to reach the target reservoir in a single run.

The new tool is a collar-mounted MWD tool designed to operate reliably and continuously—not merely to “survive”—in circulating temperatures as high as 200 C (400 F) and pressures up to 30,000 psi. It provides directional and inclination surveys, annular and internal pressures, azimuthal gamma ray, and shock and vibration MWD. Existing high-temperature electronics systems typically harness ceramic-encapsulated chips mounted on plastic boards, which begin to deteriorate and crack once temperatures rise above 175 C. By completely removing the plastic elements from the BHA, the new proprietary microchip modules that comprise the MWD and RSS electronics are designed for purpose rather than merely surviving at higher temperatures, operating normally up to 200 C.

By deploying the new HP/HT MWD tool in the Gulf of Thailand, the operator’s first well successfully drilled the reservoir section in one run, even though the temperature reached 186 C (367 F). No additional trips were required for maintenance or a gyroscopic survey. Afterward, the tool was serviced locally to ensure it was still in good condition. Then it was deployed in four more wells without further maintenance, performing for a total of 256 hours. Maximum recorded temperatures in those wells ranged from 183 C to 193 C (361 F to 380 F).

During 2013, the operator used the new HP/HT MWD tool in 10 wells, encountering a maximum temperature of 193 C. Every well section was drilled in one run, saving 12 to 24 hours per well compared with previous wells. Given the operator’s HP/HT drilling plans, reducing drilling time by even half a day per well would save 25 to 37 days per year, saving about $3.5 million per year, substantially reducing rig costs and bringing gas production online sooner.

The combination of MWD and RSS services rated at 200 C now provides E&P companies reliable directional control under HP/HT conditions.

Latin America case study

An operator in Latin America was developing offshore reservoirs in abrasive rock with compressive strength around 25,000 psi, circulating temperatures above 150 C and pressures of more than 15,000 psi. Wells had low ROPs, and downhole tools suffered high failure rates. Drilling a typical 8½-in. section required multiple runs and took 30 to 35 days.

Using a conventional directional BHA with either motors or RSS rated up to 150C, the operator started drilling another deviated well with an expected bottomhole temperature of more than 170 C (338 F). When the tool reached its technical limit, drillers replaced the existing drive system with a conventional stabilized BHA and continued drilling blind. Without much directional control, the trajectory began deviating from the plan due to the well inclination and hard formation. Without altering the path, the wellbore might have missed the target objective altogether.

At that time the new HP/HT RSS had been introduced in the region, and a decision was made to use it to correct the well trajectory and finish drilling the 8½-in. tangent. The HP/HT RSS uses push-the-bit technology and the same ceramic electronics as the HP/HT MWD tool, and its bias unit replaces a large elastomer seal with a metal-to-metal seal. Without the use of plastic components within the electronics, the HP/HT RSS operates reliably and continuously at temperatures up to 200 C and pressures up to 30,000 psi. What’s more, the entire BHA runs on downhole turbine power instead of batteries, eliminating time limits on runs due to previous power constraints and HSE concerns of hazardous materials. It also decreases the environmental footprint by eliminating waste.

By deploying the new HP/HT RSS, drillers successfully corrected the well trajectory from 77 degrees to 57 degrees, completing two consecutive runs with a single tool in the same hole. They recorded a maximum bottomhole temperature of 173 C (344 F) and pressure of 16,000 psi. In addition, the RSS achieved an average ROP of 3.84 m/hr (12.6 ft/hr), which was 16% faster than the previous record for the field. The well was finished in 18 days rather than the planned 27 days. Reducing the drilling cycle by nine full operating days saved the company $1.35 million in rig costs alone.

Integrated solution

In 2012 the industry spent an estimated $21 billion for HP/HT operations, often in very complex wells and areas with high geological uncertainties where real-time measurements and directional services can determine the difference between success and failure. For the first time, a unique new HP/HT MWD service and HP/HT RSS provide operators with a fully integrated HP/HT logging and drilling solution, permitting operators to reach further and deeper into harsh HP/HT conditions in search for more oil and gas without compromise. Instead of tweaking legacy technologies to survive longer in HP/HT environments, the new HP/HT BHA was engineered specifically to thrive under extreme conditions. Currently, HP/HT RSS and MWD systems/BHA are used in four different places around the world, enabling operators to reach hot and deep challenging wells in HP/HT environments.