Both geosteering and horizontal drilling essentially became household words during the Austin Chalk drilling boom beginning in the late 1980s.
Lateral wellbores became the “in” method to tap production in the long-challenging chalk.
But drilling sideways deep within the earth while remaining in a specific zone can be tedious, to say the least. Imagine, for instance, navigating the bit within a 10-foot lateral for a distance of a few thousand feet.
To do this required geosteering technology, which basically is a means of steering the drill bit with reference to geologic markers. The markers often are the top and bottom of the pay zone, frequently defined via gamma ray or resistivity data.
Subsurface data are interpreted in real time to enable steering decisions on the fly.
“The essential idea of geosteering is to use some unique dataset to identify target versus non-target stratigraphic horizons,” said AAPG member Stephen Grimes, senior staff geologist at Empirica, a division of ALS Oil and Gas. “Usually gamma radiation is used, but also geochemical data and any other type of stratigraphic data.”
Even though geosteering continues to be used mainly for horizontal well placement, there’s change afoot.
Operators are beginning to use geosteering as a research tool to help with exploration and more advanced data analysis.
“We are evaluating the use of other technologies for geosteering, such as mass spectrometry, which analyzes mud gases in great detail,” Grimes said, “or X-Ray Diffraction (XRD), which determines mineralogy of the cuttings.”
On Your Mark(er) …
Along with the array of data now being used to optimize well placement, operators in some areas are using multiple data sets to subdivide zones and create sequence stratigraphy maps.
Empirica recently used X-Ray Fluorescence (XRF) to geosteer a horizontal well. This method bombards a powdered sample with X-rays, causing each element in the sample to emit energy at characteristic wavelengths and energy levels, according to Grimes.
“By analyzing the spectrum produced, the machine is able to determine the relative abundance of elements in the sample,” he said.
In this instance, fresh cuttings at the drillsite were analyzed using the XRF. Prior to drilling, cuttings from a vertical offset well were analyzed using the same machine and methods. Various marker beds in the play having specific major and trace-elemental properties were identified.
“As drilling and XRF of the new well advanced, we were able to identify the marker beds and guide the client to steer the well to stay in the pay zone,” Grimes said.
The result: The operator managed to stay within 13 feet of the well’s target line.
“Additionally,” Grimes added, “our onsite mass spectrometry of the mud gases helped ensure the beds being drilled were actually productive zones.”
Science to the Rescue
The industry is waiting on the next big breakthrough for horizontal wells, according to AAPG member Josh Dill, remote operations manager at Empirica.
He mentioned the Permian Basin as being a kind of experimental locale.
The Permian is a happening place for operators these days, and there’s burgeoning interest in horizontal drilling in this old oil patch jewel, where vertical wells have traditionally been drilled.
“People are interested in what they can do to maximize economics out there as to horizontal drilling,” Dill said.
“It seems to be a sort of testing ground to see how that goes,” he added. “The work there seems to be using a lot more science to maximize profitability.”