Abstract

Exploration activities in Kuwait involve drilling of HPHT wells to search for high quality oil from the Jurassic formations. The wells drilled are very challenging with deep horizons (~16,500 ft), over-pressured formations and zones with narrow pore/fracture pressure windows which require the setting of multiple casing strings.

It is imperative that surface/intermediate casing strings are run to the maximum depths possible in order to reach well TD in a workable hole size. This presents the challenge of drilling long sections of large diameter hole in an acceptable time frame while maintaining borehole quality such that the big diameter tubular strings can be successfully run.

This paper will discuss the challenges of drilling 22" hole in such wells from 6,000 to 9,500 ft and the potential to replace established methods with new technology solutions to improve drilling performance.

The conceptual project consisted of an attempt to replace multiple 22" insert bits, rotary driven, with a single PDC bit design run on downhole motor. A partnership approach was initiated with the bit manufacturer and motor provider. Bit designs, downhole motor and rig equipment specs were developed and improved on over the project.

Bit and motor combinations were tested over a number of wells using several drilling rigs. The performance improvements were benchmarked with the original method. Over the trial, the goal was to try and drill the entire section with one bit from shoe to shoe, thus cutting interval costs and drilling times.

This paper will detail key factors in drill bit design, analysis of downhole motor performance, plus the critical role of 'state of the art' rig equipment. It will present a case history of this 'design and development' process with conclusions which provide the basis for future optimization of the technology.

Introduction

Kuwait Oil Company has been involved in the drilling of HPHT exploration and appraisal wells in the North Kuwait area for the last 10 years. Recent finds of commercial quantities of hydrocarbons in the Jurassic horizons has resulted in the launching of the 'North Kuwait Gas Development Project' covering the production of gas and light oil from six of the north Kuwait oilfields.

The development of the North Kuwait Jurassic Project is a major project with a planned production growth up to 1,000 MMscf/d of gas and 350,000 bbl/d of light oil by the year 2015. To meet these production rates a total of 70 new wells are planned to be drilled by 2015 followed by a further 20 wells to sustain the production plateau rates.

In this transition phase between Exploration/Appraisal and Development well activities, it was necessary to change the approach to the drilling of the wells in order to reduce overall project timing and cost. A re-think of present drilling methods was necessary and the application of new technology solutions was needed to optimize drilling times.

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