Efficient Drilling of Ultra-HP/HT Wells in the Gulf of Thailand

Topics: HP/HT
Fig. 2—Arthit and Bongkot fields.

A new measurement-while-drilling (MWD) tool has been designed that can operate reliably at 200°C and 207 MPa, providing real-time direction and inclination surveys, azimuthal gamma ray, annular and internal pressure while drilling, and shock and vibration measurements. An operator in the Gulf of Thailand used this new MWD technology to drill wells in ultrahigh-pressure/high-temperature (HP/HT) reservoirs without the need to stop operation because of temperature limitations. Savings of ½ day per well have been achieved.

Introduction

Offshore drilling in the Gulf of Thailand increasingly challenges logging operations, with temperatures greater than 200°C. Hundreds of wells need to be drilled per year in this environment to fulfill long-term gas contracts. High efficiency is required in such a high-volume operation.

Existing commercial MWD and logging-while-drilling (LWD) technologies are only capable of operating up to 175°C, with an inherent decrease in reliability at higher temperatures. In the planned ­ultra-HP/HT projects, the bottomhole assembly (BHA), which includes an MWD tool for directional and inclination measurements in real time, will be pulled out of the hole once the circulating temperature reaches 175°C. Then, a new BHA, without measurement tools, will be used to continue drilling to total depth. This “blind” drilling section could be several hundred meters long, introducing risks associated with well control and well collision.

The main limiting factors in having MWD/LWD tools operating in these ultra-HP/HT environments are the downhole electronic components. Industry research studies show that plastic-­encapsulated components have a life expectancy of approximately 1,000 hours at 150°C; this drops to less than 100 hours at 175°C. Ceramic-encapsulated components last longer at 175°C, but they are bigger and heavier than their plastic counterparts. Because space is restricted in these tools, the best compromise yields a mix of both ceramic- and plastic-encapsulated components.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 25392, “Efficient Drilling of Ultra-HP/HT Wells in the Gulf of Thailand,” by Joy Araujo, Schlumberger; Keittipong Kaotun, PTTEP; and Panupun Dumrongthai and A. Adrian, Schlumberger, prepared for the 2014 Offshore Technology Conference, Houston, 5–8 May. The paper has not been peer reviewed. Copyright 2014 Offshore Technology Conference. Reproduced by permission.
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Efficient Drilling of Ultra-HP/HT Wells in the Gulf of Thailand

01 April 2015

Volume: 67 | Issue: 4

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