Extended Well Tests (EWTs) are gaining increasing recognition throughout the offshore industry as a useful tool for evaluation of field development prospects. These tests, which can range from a few weeks to several months in duration, provide valuable data for reservoir evaluation and design of field development facilities. This paper describes how a contractor serving as project manager supported Texaco North Sea (UK) Company in the planning, organization and execution of a fast-track EWT at the Captain field prospect offshore Scotland.
In November 1992, Texaco North Sea (UK) Co. awarded a contract to Oceaneering to perform project management services for an extended well test (EWT) of its Captain prospect. Captain is located in the Moray Firth, Block 13/22 of the UK sector, 90 kilometers east of Wick, Scotland, in 107 meters of water, Fig. 1.
The field was discovered in 1977 when an exploratory well encountered 191 feet of oil-bearing sand. Further delineation followed in 1989 and 1990 with additional wells. A well to the north in 1989 found 93 feet of oil sands and flowed at 740 BOPD using an electric submersible pump (ESP). It was determined that horizontal wells were necessary if commercial production rates were to be achieved. In 1990, one horizontal well was drilled. Again using an ESP, it produced 6,500 BOPD of heavy 19Degree API gravity oil. From this and other data it was theorized that there might be about 200 million barrels of recoverable oil in the field.
The EWT program was originally scheduled to commence with the drilling phase in January, 1993, and to conclude following a 90day extended well test in September. During the test phase, the produced crude would be Processed by equipment installed a board a semisubmersible drilling rig and exported to a storage tanker as clean stabilized crude oil.
The purpose of the extended well test program was to confirm the magnitude and producibility of the Captain field. Test results would be used to determine sustainable crude oil flow rates and the probability of early water cuts which would impact field economics. This information would contribute to design of the eventual field development program and facilities. It was very important to test the oil and water separation techniques the high viscosity crude with the ESP-induced emulsions.
The main task a fix the EWT program included the following:
Establish appropriate management systems and Procedures
Finalize vessel and hardware subcontracts
Finalize flowline design and submit it to regulatory authorities
Direct requisite rig modificationsto accommodate the process facility
Ensure timely detail process design and fabrication.
The main EWT system components used during execution of the well test program were: the spread-moored semi- submersible which drilled the wells and later served as the test platform for the process equipment; the process system; the flexible export flowline and the dynamically positioned storage tanker, Fig. 2.
