Session: 11-02-01 Well Drilling Fluids & Hydraulics

Paper Number: 127485

127485 - Transient Hole Cleaning Behaviour: What Can We Learn From Flow Loop Experiments 

Ensuring adequate hole cleaning is important for safe, efficient and economic drilling operations.  Most models and flow loop experiments assume steady-state conditions.  From experiments it is possible to derive empirical and semi-empirical equations for cuttings holdup and pressure loss.  The conservation equations of more physics-based models are also greatly simplified.

Drilling is an inherently transient process.  Even in the steadiest situation, the drill bit position advances continuously.  When inserting a new stand of drill-pipe there are transients in both string rotation speed and flow rate.  Additional transients occur when the drill-pipe is rotated and reciprocated to clean the wellbore. When drilling wells with a narrow pressure margin it is important to control and limit such pressure peaks.

We have conducted flow loop experiments in a drilling fluid rig with a 10 m long inclinable test section to investigate hole cleaning performance of field applied oil-based and water-based drilling fluids.  While the focus of the experiments has been on steady-state performance, the experiments also provide insight into the transient performance.  In a controlled laboratory setting transient signal responses provide quantitative information on cuttings entrainment and settling processes, which can be used for model closure development.  With the introduction of Along-String Measurements (ASM), transient responses may provide additional information on the presence of cuttings accumulation, both with respect to location and quantity.

In this paper we present a quantitative analysis of two types of transients observed in our experiments: a) the so-called alpha-wave type transient which is seen when starting cuttings injection with a too low flow rate, giving insufficient hole cleaning and b) the pressure surges which are induced by a step-wise increase in either flowrate or string rotation speed.  The first case corresponds to the start of drilling of a new length of drill-pipe stand and will usually give a slow increase in pressure gradient without overshoot.  The second case is characterized by a sharp pressure peak followed by a more gradual decline in pressure as the hole is being cleaned.

Presenting Author: Jan David Ytrehus SINTEF

Presenting Author Biography: He holds a Master of Science degree in mechanical engineering from the Norwegian University of Science and Technology (NTNU) with fluid mechanics as main area. Currently he is a senior scientist at SINTEF Industry. SINTEF has been his employer for more than 20 years and he has worked with oil field development, production, wells and drilling issues. He has managed projects for many Clients, such as the Research Council of Norway and Norwegian and International service and operating companies. His main field of expertise is within drilling fluids & well technology.

Authors:

Bjørnar Lund SINTEF
Ali Taghipour SINTEF
Arild Saasen University of Stavanger
Jan David Ytrehus SINTEF