Sampling the pre-salt

Antônio Mataruco, Flávio Dias, and Fernando Marcançola

August 1, 2014


Internal and external rupture disks. Photos from Halliburton. 

Halliburton’s Antônio Mataruco, Flávio Dias, and Fernando Marcançola discuss the first fully acoustic-telemetry downhole sampling operation in a pre-salt environment in deepwater Brazil.

The new oilfield reserves recently discovered in Brazil have been located in more hostile environments than previously explored; these investigations had not been pursued earlier, because until recently, no technology was available that would allow safe investigation and production in the deeper, more hostile environments. In addition, it was not feasible to attempt to research these areas, when considering that drill-stem testing (DST) operations require reduced pressure applied to the annulus to operate the downhole tools. In addition to safety, economics also was an important consideration because of the various wireline operations that would be necessary.

Fluid sampling operations are very important for reservoir evaluation. But, to consider testing in the deep, more hostile environments, the methods traditionally used for conducting sampling had to be adapted to the new scenarios, before they could be considered for accurate testing operations. The goal of this discussion is to review a case study in deepwater Brazil to explain how a testing application using acoustic telemetry technology was capable of operating in the hostile conditions to perform the diagnostics required from downhole fluid samplers.

Representative reservoir fluid samples are essential prerequisites for providing quality fluid properties and characteristics. Accurate sampling techniques often provide critical input to reservoir simulation models and help to optimize processing of facility designs to help boost the profitability of an oil or gas field. A physical sample of the reservoir fluid is also crucial for defining the potential monetary value of a hydrocarbon reserve.

Acoustic telemetry systems help optimize operational cost because of their capability to quickly access real-time data pertinent to the reservoir evaluation, thus allowing immediate well-timed decisions or changes to be made to DST operations.

For the first time, the major operator in Brazil made the decision to use real-time acoustic telemetry to monitor and control a DST operation. The job was conducted from a semisubmersible rig, at 7053ft water depth, in the pre-salt region of southeast Brazil, in a well 17,600ft deep.

The bottomhole sampler is one of the most important tools in a drill-stem testing operation. It is responsible for collecting the first representative sample of the fluid produced by the reservoir. Its operation was usually performed by the actuation of rupture disks. Up to three different disks could be installed, allowing the actuation of the sampler in three different times of the testing. Each rupture disk was connected to three different samplers, totaling a quantity of 3600-cc of representative samples.

On the other hand, adapting the pressure ranges of each rupture disk demanded predetermined calculations. Besides the samplers, all the rupture disks used for the downhole tools were required to be within a tight range that had to be determined by the pressure to which the casing has been previously tested.

Using acoustic telemetry-operated triggers, the samplers can be actuated by rupturing internal disks, which are not dependent upon the annulus pressure.

Acoustic telemetry communication with the bottomhole samplers provided important advantages to the client:

In this DST, the acoustic triggers were actuated on the 15th day of operation. The acoustic command was sent and received downhole successfully. It was confirmed because of the feed-through capability of the acoustic system. The “fired” diagnostics status was sent, after the sample had been collected.

On the 37th day of operation, the bottomhole sampler was pulled out of the well. The downhole sampler’s rupture disk was intact. Then, it was possible to visually confirm that the bottomhole samplers had been acoustically actuated (See figure 1).

A pressure and temperature gauge installed on the nitrogen chamber of the bottomhole tool also confirmed the actuation of the nine samplers at the same time. The gauge allowed the reservoir engineer to confirm that the sample bottles had maintained the reservoir pressure. This ensured that the collected fluid had contained all the physical and chemical characteristics required. The verification that annulus pressure provided showing that the sample was collected acoustically is shown in the graph.

The black line shows the pressure data collected by the gauge installed on the nitrogen chamber of the bottomhole sampler. The blue line represents the annulus pressure. In fact, the nitrogen pressure did not change when the annulus pressure was applied. This is another reliable indication that ARMADA bottomhole samplers were actuated acoustically.

As presented, the results proved the success and quality of the sampling operation, in a reliable and distinctive manner. The operational safety is a great advantage, as the use of annulus pressure can be largely minimized.

Annulus pressure ensuring sample was collected acoustically. Source: Halliburton.

A benefit of the wireless operation, the acoustic method of actuation of the ARMADA bottomhole samplers has the potential to save days of rig time. Once the reservoir and well engineers define the proper moment to actuate the samplers, a single click on the control computer will start the process. Additionallty, the risk of repeating sampling operations due to the collection of unrepresentative samples is very unlikely to happen. Constant monitoring of the pressure and temperature of the sample guarantees that it has been monophasic during the entire test.

Recently released by Halliburton, the RezConnect well testing system provides an acoustic feedback feature. It allows for complete understanding of what is occurring downhole. This capability enables immediate and accurate decisions to be made during well test operations. Decisions are made in real time. Operators can more efficiently plan and achieve their intended well test objectives, with less rig time compared to conventional sampling and testing methods.

Using Halliburton’s successfully established proprietary DynaLink telemetry system, RezConnect well testing system integrates all the DST tools and allows surface verification of operational status.

Flavio Dias 
joined Halliburton in 2001 as a data acquisition specialist for testing and subsea (TSS). In 2004, he worked overseas, developing skills on surface well testing technologies. After his return to Halliburton in 2007, Flávio worked as a TSS field engineer, testing offshore coordinator and DAS shop supervisor. From October 2012 to March 2014, he was the testing and subsea technology technical professional engineer for Latin America, based in Carrollton, Texas.  Flávio currently works on the TSS business development team in Southeastern Brazil.  Flávio holds a degree in petroleum engineering from Universidade Estácio de Sá.

Fernando Marcancola 
has over six years of oilfield experience in deepwater exploration as a reservoir field engineer in Brazil. In 2013 Fernando held an assignment at Halliburton’s Technology Center in Carrollton, Texas, supporting operations and technology for well testing operations, focused mainly on telemetry controlled well tester valves. Currently he  is a project team coordinator for Halliburton’s Testing and Subsea product service line in Brazil. Fernando holds a degree in control and automation engineering from Universidade Federal de Itajubá in Brazil and is currently pursuing a Master’s degree in petroleum engineering at Heriot Watt University.

Antonio Mataruco 
joined Halliburton in 2009 as a testing and subsea field engineer in the sampling sub-product service line and worked with Sampling in Brazil and Mexico. He was promoted at the end of 2013 to the shop supervisor position. Antonio holds a degree in production engineering from Universidade Federal de Itajubá.