Abstract

Cuttings transport has been the topic of theoretical and experimental studies for many investigators, who have always focused, due to the complexity of the subject, on steady state flows. However, the adequate representation of the involved phenomena requires more realistic simulation of the process, which is typically transient. The test results presented here relates to the erosion of a solids bed, formed in a full scale flow loop, by different polymeric suspensions in annular flow, at several values of flow rates, wellbore inclinations and drillpipe rotational speeds. Adequate instrumentation allowed for the recording of the evolution of solids concentration and bed height as function of time. Analysis of the experimental data enables the prediction of the rate and time of erosion of the cuttings bed and can be used as guidelines for the optimization of the circulation of horizontal and highly inclined wellbores.

Introduction

The action of stopping drilling to flush cuttings out of the well is always a point of controversy among oilfield teams. The practice of circulating periodically the hole may avoid several operational problems during the drilling of a highly inclined wellbore. On the other hand, if minimum requirements for the cuttings bed removal are not achieved, circulation will be ineffective, time consuming and, in some cases, detrimental to wellbore stability.

The topic of drilled transport during drilling has been the subject of studies for many investigators (Iyoho, Sanchez, Peden et al.). who have all focused, on steady state flows. Martins et al. presented a discussion on the optimization of hydraulic parameters in the circulation of horizontal wells. In this study, the authors propose correlations for bed height prediction after circulation and for the critical flow rates for complete removal.

The development of drilling activities requires more realistic simulation of the process, which is typically transient, due to interruptions in the operations and instabilities of rock formations, which tend to generate higher amounts of solids than expected. Ref .4, for example, does not answer to the major question about the optimum time to circulate a well.

In the present work the authors propose a way to quantity the variation of the amount of solids removed from the annulus with time, during the circulation of horizontal and inclined wells. The main objective is to provide methods to evaluate the evolution of bed erosion for given hydraulic conditions. The study is based on an extensive experimental work conducted at University of Tulsa large scale physical simulator, as a cooperative program among PETROBRAS, SHELL INTL. E&P RTS and U. TULSA.

Experimental Facility

About 60 different hydraulic and geometric conditions were tested at the University of Tulsa (TUDRP) cuttings transport facility. The TUDRP flow loop has been designed and constructed by Stenevick and later modified by Bassal. It has been designed to simulate a wellbores in full scale and the main purpose is to perform research on cuttings transport experimentation. The flow loop is made up of a 84 ft long test loop section, composed of a 4 1/2 in drillpipe and an 8 in transparent acrylic outer pipe. Other components are a mud tank with an agitator of 85 bbls volume capacity, two parallel duplex mud pumps (one driven by a six cylinder diesel engine and another by an electric motor), flow lines connecting pumps via test loop section to mud tank, a cuttings injection tank and a cuttings collection tank (Fig 1).

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