Offshore Northern Sea Case Histories of the Environmentally Friendly Testing Vessel, the "Crystal Sea"
Authors: Tjelta Odd , Ashwell Charles , Statoil Odd , Taylor Robert W. 
Published: October 2008

One of the problems that surfaces during offshore well test operations, stimulations, and routine work over's has been the discharges that are made into the air and sea, and in particular, the possible formation of dioxins during the combustion process. Since these operationsand tests have normally been performed by mobile drilling rigs that do not have storage capacity, oil and gas sequestered during performance of the procedures are burned off from the rig flare booms. Another major problem during well testing has been the incapability of the flare to operate at high flow rates. Since the burning process slows down the pace of a test and does not allow the well to be tested under full flow, valuable information about the well that would otherwise have been available cannot be determined.

In addition to the possible environmental dangers and losses of important data resulting from the decreased flow rates during testing, the flaring of hydrocarbons represents an economic loss. For example, in the case of oil rigs, the flaring process not only emits C02 into the atmosphere but also burns off oil during pursuit of its operations that could be sold or used.

In light of the economic and regulatory changes occurring in todays oil and gas industry, the justification for development of a cost-effective, environmentally safe lternative to flaring hydrocarbons was certainly indicated.

This paper will discuss the well test vessel, "Crystal Sea," and the initial two jobs on the Stafford North Satellite Field in the Norwegian sector of the North Sea. A map of the field location is shown in Figure 1. The success of these jobs confirms that the Crystal Sea canprovide an alternative to flaring that reduces the degree of pollutants discharged from oil rigs, and at the same time, can salvage the usable oil. The sale of the salvaged oil, which would normally be lost during the laring process, often can generate sufficient economic return to pay for the vessel.

"Crystal Sea" is capable of receiving products at approximately twice the flow rate as is possible with conventional surface test equipment from a rig. This increased flow rate not only improves the accuracy of the technical information obtained from the well test but also provides valuable tools for improved reservoir management.

INTRODUCTION

Flaring is done during well testing operations that are Normally performed to determine the size, viability, and optimum production capabilities of an oil field under exploration. The flaring of hydrocarbons on the Norwegian Continental Shelf is regulated by thePollution Control Act and is subject to very tight approvals.1,2,3,4The levying of taxes amounting to more than $228.5 million by the Norwegian government in 1992 exemplifies the extent of this problem. Additionally, mobile drilling rigs on exploration contracts or platform rigs under production, normally test the upstream slurry mix of gas/oil/water/mud and variousminerals from time to time. These tests are carried out and processed onboard the oil rig, taking samples from the mud/drilling fluids.