Automatic MPD & downhole temperature estimation and temperature effect on density

Abstract

Hydraulic model is the ‘brain’ of an automated managed pressure drilling (MPD) control system. It requires knowledgeable people to set up and tune before operation starts. Glenn-Ole Kaasa’s simplified dynamic wellbore model has been often utilized in recent years. It is able to model fluid flow during drilling under the condition of uniform flow pattern in the drillstring and annulus along the complete length. In this study, on the basis of the Kaasa’s model, a simulation of backpressure pump (BPP) method was given for the purpose of demonstrating automatic pressure control during a drillpipe connection process. A primary challenge during drilling high temperature and high pressure (HTHP) wells is to maintain a constant bottom hole pressure (BHP) in a relatively narrow operating window. Temperature plays a very important role on density determination. A small change in density can cause great pressure fluctuation in BHP. In this study, the downhole temperature behaviors are predicted for a circulating well on the basis of Eirik Kaarstad’ work[1], then couples this temperature model into a linearized density equation in order to study the downhole density under isobaric condition. The model is valid for using of incompressible drilling fluid. It assumes steady-state heat transfer in the wellbore and transient heat transfer in the formation. A large number of sensitivity analysis are performed in this study based on the temperature and density model. The results provided by these comparisons show how those different variables with variety of values can influence the temperature and density behaviors under circulation condition and moreover to what extent the temperature and density were affected. It gives a very good picture of dynamic downhole temperature and density behaviors.