Drilling optimization can be defined as the provision of real-time data to expedite decision-making based on information transmitted from downhole. Trends in data need to be looked at to derive accurate conclusions about bit status, weight transfer, drilling dynamics situation, hole quality, etc. — all aimed at achieving enhanced wellsite efficiency and increased bottomhole assembly (BHA) reliability.

INTEQ has launched the CoPilot real-time drilling optimization service built around a versatile downhole data acquisition and diagnostic tool. The downhole sub contains a variety of

The bending moment is a key CoPilot measurement, especially when drilling 3-D directional wells. This measurement represents the bending stresses in the BHA caused by well bore curvature and gravity. (Image courtesy of INTEQ)
sensors to measure downhole weight-on-bit, torque, pressure, accelerations, and rotation. All sensors are connected to a high-speed (1,000 Hz) data acquisition and processing system that continuously analyzes the incoming data stream. As an industry first, the CoPilot tool also measures the bending moments in the BHA generated by the side forces at the bit and other wellbore contact points. Inside the tool, two strain-gauge measurement bridges are installed perpendicular to each other to measure the bending stresses acting on the rotating BHA. The total bending moment is determined as the vector sum of the individual signals of the two axes.

The bending moment information along with other key drilling mechanics and dynamics information is transmitted to the surface via mud pulse telemetry. Presented on a display along with surface-acquired data, CoPilot information provides real-time insight into the downhole drilling and logging environment. Based on the feedback from downhole, corrective action can be initiated as required and its effects monitored.

As an example, the bending moment data provide continuous information about the dogleg severity of the well bore as opposed to the directional survey data typically taken every 100 ft (30.5 m) in standard directional drilling operations. If the development of a local dogleg is detected, INTEQ’s AutoTrak Rotary Closed Loop System BHA steering parameters can be adjusted immediately via downlink to counter the deviating trend.

The effectiveness of the system has been proven in drilling complex 3-D wells in difficult formations. Specific drilling procedures have reduced the severity of local doglegs, allowing smoother, longer lateral drains to be drilled in fewer runs and shorter time.

Case Study: Troll field

Troll field, the world’s largest offshore gas field, is located 50 miles (80 km) off the west coast of Norway at a sea depth of about 1,098 ft (335 m). Operated by Hydro, the field consists of the gas-producing Troll East sector, and Troll West, where recoverable oil lies under the gas cap.

Troll oil consists of thin oil-bearing layers that lie beneath the huge Troll gas reservoir in the North Sea. Large volumes of oil spread out through an area roughly 173.7 sq miles (450 sq km).

Hydro has developed Troll’s oil resources with the use of more than 110 horizontal wells,
A trilateral well in Troll field included a challenging 180° azimuthal turn. Monitoring of the bending moment and other drilling mechanics and dynamics data allowed immediate actions to be taken whenever a high, local dogleg was being formed due to calcite intersection. Run lengths were extended considerably; the entire well was drilled with just three BHAs with a total reservoir exposure of 26,083 ft (7,950 m) and 35.5 days ahead of the original schedule. (Image courtesy of Hydro)
positioned accurately about 1.5 ft (50 cm) above the oil/water contact and the thin sands between 88.5 ft and 26 ft (27 m and 8 m) thick. Applying field-specific multilateral technologies, complex horizontal wells with up to six producing extensions have been drilled.
Compared to conventional wells, multilateral wells have slowed down the rate of gas breakthrough and sustained initial production rates for a longer period of time, resulting in improved oil recovery and well life cycle.

The Troll reservoir formation consists of relatively loose sandstone and local hard calcite-cemented zones, which pose a constant challenge to directional control. Depending upon the orientation of the calcite interval and the drilling parameters when entering or exiting the calcite, the drill bit can be forced aside to create a potentially severe local dogleg. High local doglegs can introduce significant stresses in the BHA that can rapidly accelerate fatigue of the BHA components and connections. In addition, local doglegs can cause severe drillstring and casing wear and pose a limitation to the lateral reach of horizontal wells.

A trilateral well was a particularly challenging profile including a 180Þ azimuthal turn. The modular architecture of the AutoTrak rotary steerable system made it possible to position the CoPilot tool directly above the steering unit close to the bit. Monitoring of the CoPilot bending moment and other drilling mechanics and dynamics data allowed immediate actions to be taken at the earliest stage whenever a high, local dogleg was being formed due to calcite intersection. Run lengths were extended considerably; the entire well was drilled with just three BHAs with a total reservoir exposure of 26,083 ft (7,950 m) and 35.5 days ahead of the original schedule.

Case Study: Gulf of Mexico

The drilling program for an operator in deepwater GOM required hole enlargement operations while drilling through a salt section in a field located offshore Louisiana. Two offset wells encountered drillstring twist-offs within 1,000 ft (305 m) of the top of salt, presumably due to excessive vibrations. The twist-offs resulted in fishing operations and caused a significant time delay with respect to planned drilling days. It was also reported that the rate of penetration (ROP) was low in the salt due to weight transfer problems to the bit.

The operator decided to employ the CoPilot real-time drilling optimization service in conjunction with the AutoTrak rotary steerable system to mitigate possible twist-off, reveal critical downhole dynamic situations, determine the weight-on-bit as compared to downhole weight-on-reamer, downhole torque, and downhole rotation speed (RPM). Such real-time downhole information allowed for necessary adjustments to drilling parameters to ensure safe and efficient drilling from casing shoe to casing shoe in one single run without failure.
Specifically, as compared to the offset wells, immediate parameter adjustments in reaction to transmitted backward whirl diagnosis contributed to twist-off prevention.

For example, high lateral vibrations with energy content in the range of 5 to 15 g RMS (root means square)(lateral severity 4 - 6 on a scale 0 – 7) were reduced by adjusting drilling parameters down to 100 RPM and a steady weight-on-bit of 40,000 lb. These parameter changes not only reduced the downhole vibration level but also helped to increase the net ROP by 15% in comparison to the offset wells.

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