You could write a book describing all of the ways oil explorationists have tried to acquire formation fluid samples over the years. Most of the techniques were successful, but there was always something that left the engineers unsatisfied. We should rule out the earliest “successes” like Spindletop, where Capt. Anthony F. Lucas and his associates were presented with a formation fluid sample of almost a million barrels right in their faces, so to speak.

Discounting the gushers, the first viable formation fluid samples were obtained when the brothers E.C. and M.O. Johnston introduced drillstem testing to the industry in 1927. The biggest advantage of their method over past attempts was that the well was under control, and a sample could be retrieved without drenching the lease and surrounding areas. But giving a viable fluid sample to explorationists was like giving candy to a baby. They just wanted more — more timely, more economical, more pure, more accurate. And so, the race began.

Steady improvement in fluid sampling was forthcoming from the service industry with a variety of formation tester tools spanning the last 60 years or so. Each generation of testers brought advantages. But the “holy grail” has always been the ability to acquire fluid samples while drilling. The task was daunting.

With the introduction of its GeoTap formation pressure-while-drilling technology (FPWD), Halliburton threw down the gauntlet that launched the development of several pressure-while-drilling solutions by various companies. Development was not without its challenges. Building tools that could survive the drilling environment was difficult enough. Getting them to set reliably and measure formation pressure accurately in a timely manner, then repeat the process over and over, required years of work and rigorous testing.

To its credit, the industry recognized that FPWD represented a valuable addition to its formation and reservoir evaluation capabilities, and many innovative applications ensued. These included pressure and fluid mobility profiling and compartmentalization determination. But the customers were still thirsting for a drillstring tool that could actually acquire and retrieve a representative fluid sample. The latest development, Halliburton’s GeoTap IDS, promises to do just that.

Actually, the new system goes beyond simply acquiring a fluid sample. It includes the ability to set on a particular formation, verify the hydraulic seal, and pre-test to obtain formation pressure and mobility data. Once these basic measurements have been completed and data sent to surface using either mud-pulse telemetry or wired drillpipe telemetry, the decision can be made to obtain a sample. A flowline inside the tool is opened and fluid is produced with the help of an internal pump, then expelled into the borehole annulus. As fluid passes through the flowline, it is analyzed using a series of sensors to determine its relative quality.

Even though formation sampling-while-drilling is performed closely behind the bit, it is possible that some drilling mud filtrate has invaded the porous and permeable formations, contaminating the formation fluid. By measuring the fluid’s pressure, temperature, resistivity, and dielectric constant in the flowline, its degree of filtrate contamination can be assessed. When flowline measurements confirm that pure formation fluid is being produced, a decision can be made to commit a sample chamber to receive it.

GeoTap IDS comes with collars containing five removable sample chambers each. Three or more of these collars can be run in tandem in the bottomhole assembly, providing the ability to acquire 15 or more individual formation fluid samples. The company introduced GeoTap IDS at the Society of Petrophysicists and Well Log Analysts’ annual meeting this June in The Woodlands, Texas.

The “holy grail” may be within reach at last.