A Simplified Jet Pumping System for Exploration Testing in an Offshore Environment
Authors: Bryant R. , Hampton P. 
Published: October 2008

This paper reviews the system selection process and implementation of an artificial lift system (jet pump) for drillstem testing a heavy oil exploration prospect in a mobile offshore drilling unit (MODU) environment.

The application of artificial lift technology on a floating semi-submersible while exploration drilling is the first of its kind in Canadian waters and is unique by virtue of the system's simple and self-contained configuration.

The system was comprised of a reverse circulated jet pump set into a conventional 3.5 inch drillpipe test string. Power fluid for pump operation was routed down the anulus via the marine riser kill line using the drilling unit cement pumps. Reservoir fluids were entrained in the power fluid stream at the jet pump and produced up the test string. Surface handling and storage requirements of fluids were minimized with a simplified separator configuration and by recirculating power fluid for re-use.

Actual field operation of this system proved it to be a safe and effective means of employing artificial lift to an offshore exploration testing program.

INTRODUCTION

With increasing frequency, heavy oil reservoirs in the offshore environment are being recognized for their massive development potential.1 Technology improvements have made evaluation of these reservoir types at an exploration stage more common, although testing programs often have either extensive equipment requirements or are of limited scope.2,3

While drilling an offshore exploration well, a relatively shallow, oil bearing sandstone was encountered. Wireline sampling (RFT) of the zone recovered heavy oil (12 deg API).4 Exploration objectives for the area required that a production test be employed. The defined testing objectives for this zone were:Demonstrate the ability to produce reservoir fluids to surface.Capture formation fluids sample.Determine reservoir parameters.

Based on RFT results, log analysis and offset well information, it was determined that artificial iii would be required in order to produce reservoir fluids to surface.

The subject well is located on exploration lands approximately 220 miles off the east coast of Canada (Figure 1). Situated in water depths ranging from 250-400 feet, this area is known for its environmental extremes of fog and heavy seas, as well as a yearly incursion of pack ice and icebergs. Ice movement in the area often forces drilling units to suspend operations and move off location in short notice. The timing of this well coincided with the regional peak iceberg period, placing additional emphasis on maintaining the ability of the MODU to suspend testing operations and move off location.

The decision to test this interval was made upon drilling through the zone which allowed very little time for planning, approvals and mobilization of test equipment. The success in quickly developing a detailed plan and implementing the program was the result of an affective team review and design process. The following discussion details this process end provides an overview of the actual testing operation.

DISCUSSION

The task of developing and implementing a testing program was carried out by a multi-disciplinary team of personnel from geology, production, drilling and reservoir engineering.