Abstract

The first horizontal well (RA-156) was successfully drilled and completed in the Lower Burgan sandstone reservoir of Raudhatain Field, North Kuwait. The objective of the well was to produce water-free (dry) oil at high rate from a difficult-to-reach portion of the reservoir. Dry production is especially desirable due to constrained wet crude processing capacity. The well successfully delivered the expected rate, making this well the highest-rate producer in the field.

Uncertainty in structure and stratigraphy are inherent in the area due to weak/noisy seismic reflections and rapid change in reservoir facies in marine-influenced channel deposits. Innovative correlation schemes and detailed reservoir description were used to reduce uncertainties. The trajectory was designed along the direction of maximum principal stress to overcome borehole instability problems. The horizontal-section was drilled with minimum overbalance to avoid potential reservoir damage.

Well-site data including logging-while-drilling (LWD), cuttings, and drilling data were used to identify faults along the well and to optimize the selection of kick-off point (KOP) and end-of-build (EOB). Subtle markers were identified while drilling, and the trajectory was geo-steered within the channel sand while maintaining maximum standoff from a rising oil-water contact (OWC). Absence of shale along 3000-ft of horizontal/high angle section was instrumental in faster drilling. Low mud weight was used to minimize potential formation damage caused by prolonged formation exposure to high-density mud.

The completion of the well was designed to deliver longterm high-rate dry oil production. The horizontal section of the well was cased and cemented to ensure zonal isolation. A perforation strategy was developed and implemented to encourage even flow from the reservoir along the productive section to avoid local water coning, facilitate future well intervention and increase productivity index (PI) by reducing potential skin. External casing Packers were used to further ensure isolation of across a fault in the horizontal section. 5–1/2" tubing with appropriate jewelry was selected to accommodate the expected high rate and to ensure well integrity.

The details of the multidisciplinary approach and the lessons learnt during planning and implementation of this horizontal well are summarized in this paper.

Introduction

Horizontal well technology has made rapid strides since the pioneering efforts of drilling in offshore Italy in the late 1970's. In addition to improving well productivity1, horizontal wells have enjoyed success in combating coning/cresting problems, in accessing bypassed oil2, and in converting resources to reserves. In Kuwait, horizontal wells have not performed up to expectation due to various reservoir issues3. Three horizontal wells in Mauddud reservoir of North Kuwait have productivity somewhat higher than a vertical well. RA-156 is the first of its kind to be drilled in the Lower Burgan clastic reservoir.

The Lower Burgan is the main producing reservoir in Raudhatain Field, North Kuwait. Of late, the reservoir is witnessing a complex pattern of water movement in different layers leading to increasing water cuts. The existing water handling facility has reached its limit due to de-salter constraints, and there is a need to produce additional dry oil to maintain oil output at the target level. The reservoir has been exploited with vertical wells, which experience coning heights up to 40 ft. A horizontal well was envisaged to circumvent the problem.

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