Directional-Drilling Technology for Remote Intersection Between Two Wells
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 155892, ’One New Needle Technology of Remote Intersection Between Two Wells and Application in Chinese Coalbed-Methane Basin,’ by Tian Zhonglan, SPE, Shen Ruichen, and Qiao Lei, Research Institute of Drilling Engineering, CNPC, prepared for the 2012 IADC/SPE Asia Pacific Drilling Technology Conference and Exhibition, Tianjin, China, 9-11 July. The paper has not been peer reviewed.
In China, the pressure and penetration of and the water production from coalbed-methane wells generally are low. An extra vertical well is connected to the horizontal well to use a pump to remove water and to collect and produce the coalbed methane. The intersection target of the vertical well is less than 0.5 m in diameter, and the connection cannot be ensured by conventional well-path measurements. A remote-directional-drilling technique and relevant equipment were developed to guide the intersection of the horizontal with the vertical well. The theoretical principle is orientation by use of a rotating magnetic field. By processing real-time data about the rotating magnetic field, the distance and angular deviation of drilling direction can be calculated to aim the drill bit at the vertical cavity and connect the horizontal well to the vertical well.
Introduction
China has an abundant coal resource, and the total amount of coalbed-methane resources is 36.81×1012 m3 (approximately equivalent to the amount of conventional gas resources). Generally, the coalbed-methane reservoirs in China have low pressure, low permeability, and low water content. Horizontal wells and multibranch horizontal wells are used most often to develop these reservoirs. Depending on the characteristics and drainage method of the well, an additional vertical well usually is needed to produce gas from a horizontal well, as shown in Fig. 1, by placing a screw pump or rod pump near the intersection of the wells to remove the produced water. The remote-directional-drilling technique was used to connect two wells, and it is essential for drilling the multibranch horizontal wells and U-type horizontal well. The primary control technique for drilling these wells has been the use of measurement-while-drilling (MWD) technology to locate the reservoir and to control the direction of the drill bit. However, this new technique of drilling a horizontal coalbed-methane well provides a higher degree of measuring and controlling wellbore trajectory to complete the intersection of the horizontal well and the vertical well. Because the target area of the vertical well is a narrow rectangle (0.54×8 m), MWD technology cannot provide the required accuracy. Therefore, a rotating- magnetic-field-measurement method was developed. A magnetic-source transmitter is installed near the drill bit while drilling the horizontal well so that a rotating magnetic field is formed when the drillstring rotates. A signal-acquisition system is set in the intersection window of the vertical well and used to collect the rotating-magnetic-field signal to calculate the distance and direction of deviation by use of an established magnetic-field-measurement model. The remote-directional-drilling instrument was used successfully in several horizontal wells to intersect vertical wells in the Ordos coalbed-methane basin.