Abstract

Effective well cleanup during well start-up ensures efficient formation damage removal and maximises the resulting well production potential. Horizontal wells are more susceptible than vertical wells to formation damage due to the longer completion length, the longer drilling time, the potentially increased overbalance and the reduced cleanup efficiency caused by the heal-toe effect.

Extensive modelling and simulation work has been previously performed analysing the impact of formation damage and well cleanup in horizontal wells. This paper extends that work to advanced completions employing Interval Control Valves (ICVs) and Inflow Control Devices (ICDs). It reports a comparative study that illustrates the greater cleanup efficiency of advanced, long horizontal well completions over that achieved by the equivalent, conventional, openhole completion.

The highest cleanup efficiency is predicted to be achieved by an intelligent completion employing both sensors and ICVs. The well's full production potential will only be realised if a proper, real-time, cleanup monitoring and control procedure is implemented to optimise the choking strategy. Only then will the near wellbore cleanup efficiency be maximised. A dynamic well simulator has been used to illustrate the advantages of employing such a proper, real-time, cleanup monitoring and choke control strategy. This only becomes possible if an intelligent completion is employed. Sensitivity analysis is used to illustrate how an ICV completion gave the highest cleanup efficiency for almost all the parameters studied.

The single zone cleanup strategy employed by an intelligent completion requires that extra time be spent on the initial stages of the cleanup process. Guidelines are required to ensure economic as well as technical optimisation of the cleanup process. This can be achieved by use of the presented, practical downhole monitoring procedures for efficient well cleanup together with a novel procedure for identifying the time when the near wellbore region is sufficiently clean.

1.0 Introduction

Formation damage is one of the major factors controlling actual well productivity 1. This is especially true for long, horizontal wells that have been drilled and completed overbalance with water-based fluids 2, 3. Perforating may bypass the contaminated zone, but is itself susceptible to damage. It has been long recognised that well cleanup complications increase with increasing well length and number of completion zones. Cleanup management has been recognised as essential for successfully bringing the well on production with the highest possible production potential. Recent publications 4, 5 provided a qualitative discussion on cleanup as part of a comparative framework for the evaluation of the strengths and weaknesses of advanced and conventional completions. This paper sets out to quantify the advantages of advanced completions to improve cleanup by use of their permanently installed, downhole flow control equipment and measurement sensors.

Intelligent wells add additional value by providing more effective cleanup than conventional ones. Subdividing the total producing length into a number of zones which are opened successively during the well start-up period is a field proven practice that maximises the drawdown to a particular zone and minimises the chance of flow conduit blockage by deposition of produced sand. The increased drawdown created by unloading the separate well zones sequentially leads to more effective formation cleaning. This temporary zonation of the wellbore can be achieved with specially pre-installed devices (e.g. clean-out or sandface valves).

Real-time, downhole pressure data can be used to ensure that the flowing bottomhole pressure is kept above the sand production limit 6. Intelligent wells break the completion into a number of zones with downhole valves while their multiple gauges can be used to control and monitor the zonal production. They also have the additional capability of optimizing the cleanup operation.

This paper will first discuss the processes that cause formation damage in the near wellbore area due to drilling and completion fluids. We will then compare the conventional well's success in cleaning up this damage with that of an advanced well completed with either Interval Control Valves (ICVs) or Inflow Control Devices (ICDs). Finally we will develop recommendations for improved cleaning techniques.

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