Drilling of shale oil and gas presents a unique opportunity for improvement. Since many similar wells are drilled during the life of a basin, even a small improvement can produce invaluable economic benefits. Drilling data of Eagle Ford wells were collected and analyzed to identify and rank major factors affecting drilling performance and economics. Solutions were developed and applied to Eagle Ford wells, resulting in savings in both drilling fluids cost and drilling days.

Drilling data of 965 horizontal Eagle Ford shale wells drilled between 2010 and 2013 by nearly 40 operators were collected and analyzed. Well drilling history was recreated from drilling data and reports. By analyzing this large number of wells with regard to well design, drilling procedures, drilling fluids, and solids-control methods, we confirmed the significant progress made in reducing drilling days and cost while increasing the lateral length over the years. The analysis also confirmed the detrimental effects of low gravity solids (LGS) on drilling operations. By comparing drilling fluids with high and low LGS concentration, it was found that high LGS concentration (> 9 or 10%, depending on the operator and data set) were associated with about 20% higher drilling fluids cost and an additional 2 to 3 drilling days per well. LGS are known for resulting in slower drilling, more non-productive-time (NPT) events, and downhole tool failures. By focusing the analysis on the most troublesome wells, it was found that the top NPT events were tools failure, wellbore instability, lost circulation, and stuck pipe.

This paper also presents an advanced solids-control solution and the early results of applying it in the Eagle Ford basin. This improved solids-control system is based on batch processing and staged centrifugation, used in tandem with chemically enhanced flocculation. It removes the ultrafine particles that cannot be removed with a conventional dual-centrifuge system. A comparison has been made between wells drilled by the same operator and drilling rig. Although the sample size in this comparison analysis may be too small to yield meaningful statistic results, the limited data showed a drilling-fluids cost saving (including solids-control costs) of 4.2 USD/ft by decreasing dilution and chemical additions, and an average drilling-time savings of 4.4 days per well.

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