Analysis of steering in horizontal directional drilling installations using down-hole motors

Horizontal directional drilling is becoming an increasingly popular technique for the installation of pipes in urbanised environments or in locations where trenching is difficult, such as under rivers or railways. This technique utilises down-hole bits to create the bore before it is expanded with back-reamers to allow installation of the product pipe. Controlling the path of the bore is critical to the success of many horizontal directional drilling installations and the potential inability to maintain such positional control is a factor that prevents the widespread adoption of this technique in place of traditional open cut methods. Two types of drill bit are commonly used in horizontal directional drilling; shaped jet-cutting bits and bits mounted on bent-subs and driven by mud-motors, the former being utilised in weak ground conditions and the latter in stronger formations. This paper analyses a dataset of survey data from pilot bores for fifty-four HOD installations that used mud-motors to investigate the parameters that impact upon the control of the position of the drilling bit. The drives are broken down into sections of rotary and slide drilled borepath and these are investigated separately. Drilling practice, drilling equipment, length of drive and the geology in which the bore is being established will have an effect upon the ability to control the position of the drilling bit. (C) 2010 Elsevier Ltd. All rights reserved.