Schlumberger

Technical Paper: A Novel Strategy for Reducing Well Cost in the Piceance Basin by Using ECD Measurements and Air Injection Through a Parasite Aerating String

Society: SPE
Paper Number: 119964
Presentation Date: 2009
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Abstract

Drilling on top of the Mesa in the Piceance Basin presents a significant loss circulation and stuck pipe challenge to operators wanting to exploit the huge gas reserves in the area. Operators have experienced losses that exceed 4000 barrels of mud when the intermediate section is drilled using conventional techniques. This is due to a combination of natural fractures and weak rock. Various strategies have been deployed to tackle the problems, including under-balance drilling operations and Direction Casing While Drilling (DcWD). A new technique described in this paper is now the best practice for ConocoPhillips in the area. It involves acquiring realtime circulating density (ECD) measurements and control of mud weight in the annulus, using direct air injection through a parasite aerating string (PAS).

During the development stages of this new process an annular pressure sub (APWD) was run to gather diagnostic data. Analysis of the data shows conventional drilling practices often yield up to 3 ppg variation in circulating density exposed to the formation. Analysis of the data also suggests there is a fracture reopening gradient of approximately 8.3 ppg and there are huge circulating density variations during connections. The new strategy shows these wells can be drilled with an ECD in the range of 5-7 ppg using conventional water based mud systems. This strategy allows wells with a very narrow mud weight window to be drilled safely. This simple approach avoids the use of complex multiphase models, giving the flexibility to quickly deploy the technique to the well site without the need for expert personnel. The information enables the driller to control and keep the ECD within recommended limits, delivering a safe and productive well.

The alternative approach of using conventional well design techniques would result in multiple casing strings and cost overruns, while more advanced techniques such as DcWD and under-balance drilling would require specialized equipment and crews. This new technique uses existing and common drilling technologies along with new software tools for geomechanics analysis and drilling surveillance to achieve excellent results. This paper presents a simple risk management technique using today�s conventional technologies to successfully manage loss circulation risk in the Piceance basin.