Well cleanup, multi-rate testing conducted on Apia, Black Widow

Recently, back-to-back deepwater well tests were completed successfully in a low-pressure dry-gas well and a high-pressure oil well, located in the US Gulf of Mexico. The projects were Apia in Garden Banks Block 73, and Black Widow in Ewing Bank Block 966, respectively. The overall objectives of the two projects were to clean-up the wells, evaluate their production capabilities, and collect fluid and reservoir data for further prospect evaluation.

Apia is a completed gas well determined to have a sustainable flow rate of 35 MMcf/d. Particularly important to this well was the recovery of any completion fluids, so as to leave it less prone to hydrate formation during production. For Black Widow, the most important goal was that the test be completed, reservoir conditions permitting, in such a way as to enable the well to produce effectively to its host facility three miles away. The reasons for success of the operation were pre-job planning, person-to-person communication, effective meetings, and effective use and management of third-party oversight.

Planning

The pre-test Apia completion meetings were particularly important because the Apia and Black Widow would be back-to-back completions on a recently upgraded rig. Because this was the first job since the upgrade, the rig crew had not yet worked with the rig or the equipment proposed for use during the well testing program.

Extensive internal and external third-party failure mode effect analysis (FMEA) was conducted to identify risks associated with hazardous operations, and to plan appropriate contingency actions. A third party performed inspections and reviews of all engineering calculations utilized in the surface well testing equipment package design, and participated in the team building and FMEA meetings.

Both completions operations used Halliburton's real-time operations (RTOSM) data acquisition system to collect all required surface data parameters, such as wellhead pressure and temperature, and high-stage and low-stage separator readings. Real-time wellsite data was transmitted to a data hub located in Houston, where it was made available for analysis at the real time operations center, and for remote viewing on a protected Internet web site.

Completing prospects

The procedures for testing and completing the Apia prospect were as follows:

1. The well was flowed to recover zinc-bromide completion fluids. When gas began to appear at the surface, flow was diverted through test separators designed for the test program.
2. Production of brine declined over time to quantities less than 5 bw/MMcf. At this point, the well was viewed as "cleaned up." The well was shut in for two hours, gathering surface pressure data to determine whether stimulation was necessary. Small pressure losses in the near-wellbore region indicated that stimulation was not required. Tandem memory gauges were run on slickline and the well was then opened up for a multi-rate flow test. Flow was ramped up to a rate of approximately 30 MMcf/d and then stepped down to 20, 10, and 5 MMcf/d, with two-hour flow periods at each step. By starting with the highest rate, the well was cleaned up for all the following rates and stabilized more quickly at each successive step.
3. The well was then shut-in for a buildup period in order to obtain information, which with the flow rate data, was analyzed to evaluate the producing capacity of the completed well.
4. At the conclusion of the test, the BHP gauges were pulled out of the hole, making gradient-sampling stops on the way.

The procedures for testing and completing the Black Widow Prospect were similar:

1. Completion fluids were produced initially. Not long after the volume of fluids contained in the tubing and riser were produced through the testing equipment, the flow changed rapidly to high quantities of oil with associated gas. Produced crude tended to foam, but testing equipment and chemicals controlled the foaming.
2. Following cleanup, the well was shut-in for a buildup test. Analysis of the real time surface-readout bottomhole pressures indicated that the buildup test could be terminated early, and that stimulation would not be required. The well was opened up for flow on chokes of 12/64, 24/64, 28/64, and 32/64 in. for four-hour intervals to understand the flow capacity of the reservoir. The well was shut in for six hours after this variable-flow-rate test and then flow resumed. Recorded well flow rates for the chokes listed were 515 b/d, 3,513 b/d, 4,880 b/d, and 6,425 b/d, respectively.
3. The well had been closed-in for the final buildup period. On-location analysis of the surface readout of bottomhole pressures confirmed the excellent deliverability of the completion. The test indicated that the completed well was capable of producing effectively to its host facility three miles away with a sustainable flow rate of 6,500 b/d and a flowing tubing pressure of 4,362 psi.

Site equipment

Production logging services, including gamma ray, casing collar locator, production fluid spinner survey tool, quartz crystal bottomhole pressure sensor, and a bottomhole temperature sensor were standing by on the rig. Surface readout capability in real time played a critical role in helping to facilitate decisions to complete the testing operations expediently. Single-phase, bottomhole samplers and memory gauges were used for collecting PVT-quality oil samples.

The surface testing equipment packages r were designed to flow 35 MMcf/d gas and 15,000 b/d of oil, respectively. More than 2,200 ft of flow piping with diameters of 3-in., 4-in., 6-in., and 8-in. provided interconnectivity of the surface well test equipment on the Black Widow project.

For the Apia gas well test, a two-stage, three-phase well test package provided a 42-in. by 15-ft, 1,440-psi MAWP, 90 MMcf/d separator for the high stage and a 84-in. by 15-ft, 250-psi MAWP, super-separator for the low stage.

For the Black Widow oil well test, a three-stage, three-phase well test package was provided utilizing the two separator vessels used on Apia. Two 84-in. by 15-ft, 45-psi MAWP surge tanks were added at the third stage. On-site reservoir sampling and analysis services collected the desired fluid and gas samples.

Marine equipment

For the Black Widow oil prospect, a 24,000-bbl capacity test barge was used for oil storage during the flow test and a 4-in. transfer hose with quick-connects was added. Tugs provided for barge movement and monitoring once it was moored at the location. After the barge arrived at the location, the zero-discharge, oil transfer hose was lowered and connected with quick-connects.

While transferring oil to the barge, there was constant communication between the rig, barge, and tug crews. A total of 2,835 bbls of oil were transferred to the barge without incident.

Data acquisition/communications

Realtime, satellite data communications allowed full functionality of Halliburton's real-time operations or RTOSM service. Data is transmitted in real time to a data hub located in Houston, then replicated at the hub and made available for viewing in real time on a protected Internet site. The real time surface readout and data communications reduced test time by an estimated 12 hours overall.

Both wells were cleaned up and their flow capacities satisfactorily evaluated in a safe and cost-effective manner. Pre-job communications and planning activities were effective in reducing the occurrence of unscheduled events. Discussion and reviews regarding FMEA procedures led successfully to an accident-free well testing operation.