DRILLING & PRODUCTION

Limited-emission sampling, testing

One of the most important steps in the process of drilling and completing an oil or gas well is the temporary completion of the well to determine its dynamic rate through time, pressure, and fluid property data. More commonly known as well testing, this process provides valuable data that are used to determine how the well will perform under various flow conditions and its reservoir characteristics and parameters.

However, escalating rig rates, increased attention to environmental and personnel safety, drilling-rig space requirements, and limited success using traditional well test systems in heavy oil and/or unconsolidated reservoirs have substantially reduced the number of drillstem tests currently being performed.

“The FasTest system has been developed that is environmentally friendly, yet a cost-efficient replacement for selective formation testing, reservoir description tool, wireline testing, or full drillstem testing,” according to Halliburton’s Mark Favret, global product champion, Advanced Well Testing, and Henk Kool, product manager, Reservoir Information.

Reliable technique

According to Favret and Kool, the reservoir fluid sampling and testing technique can acquire reservoir fluid samples taken at in-situ conditions, as well as reservoir permeability, skin, pressure and radius of investigation information in any well, especially those drilled in environmentally sensitive areas.

It can be used, they say, for applications that include drill pipe, premium tubing, horizontal and multilateral wells (one branch at a time), and various deepwater operations. Other situations where the system would be applicable are when wireline formation sampling doesn’t yield the desired results, when a full-scale well test cannot be performed, and when perforating and testing prior to a stimulation or sand control treatment.

Performance

The company says that the system combines closed chamber testing, limited flow testing, tubing conveyed perforating (TCP), downhole test tool testing, and reservoir evaluation in one operation that offers:

•Multiple single-phase 600-cc samples per run controlled by acoustic telemetry, annular pressure, or timer

• Calculates dynamic reservoir properties, permeability, skin factor, and initial reservoir pressure

•Pressure measurements for estimating downhole fluid flow rates

• Near wellbore reservoir parameters

• Assessment of productivity potential

• Fluids, solids identification, and sanding potential

• Less surface well testing equipment required

• Production beyond filtrate damage

• Real-time downhole data collection and transfer using acoustic telemetry system (ATS)

• Real-time surface control of downhole samplers using acoustic energy transmitted through tubing walls,

• Real-time monitoring and control from office.

The system’s tools can run in 7-in. OD and larger casing and can be adapted to run with almost any size work string. All tools are rated for a 15,000 psi differential pressure at 400° F and are suitable for sour gas service at temperatures above 175° F per NACE MR-01-75.

GoM well test

In the GoM deepwater, the system was used for a major operator whose primary objectives were to calculate reservoir permeability, skin, formation cleanup, radius of investigation, and capture oil samples. Because of reservoir un-consolidation, the operator wanted the test with minimal drawdown at the sand face.

Initially, the well was perforated underbalanced using tubing-conveyed perforating guns and a nitrogen cushion.

The nitrogen pressure was bled off at a pre-determined rate to yield a constant oil rate at the reservoir followed by a shut-in to calculate reservoir permeability, skin, and radius of investigation. Then, the well was reversed out and the oil captured in a surface tank for bulk sampling. The tubing was displaced with nitrogen to achieve the desired underbalance at the formation. The circulating valve was opened and the system performed. Next, the nitrogen pressure was bled off to induce a second flow and second shut-in. Finally, the downhole samplers were triggered acoustically and the well was reversed out to conclude the test.

“The job resulted in four analyzable flow periods, decreasing skin, indicating formation clean up, radius of investigation, reservoir pressure, and a large bulk sample for flow assurance testing,” Favret said.

Offshore Brazil well test

Another system job was performed for a major operator whose primary objective was to capture clean, single-phase oil samples at reservoir conditions. Secondary objectives included reservoir permeability calculation, skin, radius of investigation, and acquisition of a bulk oil sample. Because the formation was highly unconsolidated, the test was designed for a minimal drawdown.