Abstract

As capital costs continue to escalate in the deepwater environment, there is greater pressure on operators to deliver wells in a more efficient manner. This paper will review the drilling and data acquisition strategies to successfully deliver a challenging deepwater development well. First, the well was the longest stepout and highest angle well drilled in the field to date. Second, the well targeted a fault block in a portion of the field that was poorly constrained due to limited offset well control and poor-quality seismic data. Third, the final hole section, 6,000 ft of 12¼-in. hole inclined at 48°, was to be drilled through two pressure ramps, one unstable slump zone, and one pressure regression on its way to the targeted reservoirs.

The evaluation program for the well was solely logging-while-drilling (LWD)-based and included structural dip and azimuth from density and gamma imaging sensors and formation pressures and gradients from an LWD formation tester tool. Real-time formation pressure data and rush processing of the azimuthal density image confirmed that the well had crossed an unexpected sub-seismic fault in the targeted reservoir section. Structural data derived from the density image log and projected fluid contacts based on LWD formation pressure tests were integrated into the existing field model in real time, allowing the team to quickly update its structural model, define the fault block size, and successfully plan and deliver a sidetrack well. A total of 129 pressure tests were attempted with 124 successful tests recorded (96% success rate), all while circulating to maintain wellbore integrity.

The viability and benefits of a fully LWD-based data acquisition program were proven in this challenging application, delivering improved wellbore placement and reduced drilling risk based on real-time evolution of the reservoir model.

Introduction

Discovered in 1998, the presented field is located in the Green Canyon protraction area of the Gulf of Mexico (GoM) in a water depth of 6,800 ft (Fig. 1). The main reservoir targets consist of stacked, oil-bearing turbidite sands of Miocene age, at a depth approximately 9,800 ft below mudline. The field is a large faulted anticline measuring 11 miles long by 4 miles wide (Fig. 2). Development of the field is complicated by shallow fingers of salt, which obscure the seismic imaging of the north flank of the structure and create a complex water bottom across the middle of the field, where water depth changes 2,200 ft across a one-mile width. Because of this lack of clarity on the northern flank, the south flank of the field would be initially developed via a central drill center location, designated as Drill Center One (DC1).

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