Horizontal Gas Storage Wells Improve Operational Efficiency

In the past, the Tri-Cities gas field near the city of Athens in Henderson County, Texas was an important contributor to natural gas production in the region. It is now a depleted reservoir, but its usefulness has not ended.

Depleted reservoirs, especially those near large consumption centers, provide a ready-made solution for storing natural gas—it can be injected underground into a geological formation that has already proved suitable, and withdrawn as needed to meet demand.

When Atmos Pipeline–Texas, a division of the Atmos Energy Corporation, selected the Tri-Cities site for an asset integrity review, the company engaged WSP USA to assist with analyzing the reservoir’s characteristics.

“We created a 3D reservoir simulation model to study the reservoir’s dynamic behavior so the client could properly assess how it would perform when used for storage,” said Liaqat Ali, the Houston-based reservoir engineering expert who developed the model. Ali, who is part of the industrial and energy sector’s oil and gas group, has a doctorate in petroleum engineering from Texas A&M University.

“These models also help determine the best drilling and operational strategies,” Ali added. “The fact that we have this in-house capability means we can offer our clients a complete and integrated set of services on reservoir projects.”

Five new horizontal natural gas storage wells have been drilled for Atmos Pipeline–Texas near Athens, Texas.

A Strategic Alternative

Russell Bentley, director of technical business development and WSP’s project manager for the facility’s development, noted that the existing vertical wells at Tri-Cities would not be able to “drain” the field efficiently during operations, so the project team had to look for alternatives.

“The solution that stood out was to drill a series of new horizontal wells, which would substantially improve the facility’s long-term operational performance,” he said. Optimum locations for five new horizontal wells were identified by the client and verified by the 3D reservoir model.

Drilling the wells presented some significant technical challenges. “After reaching a vertical depth of about 7,000 feet, we had to turn the wells 90 degrees to drill the horizontal sections,” Bentley said. “In addition, we were working within a very restricted natural gas zone that was in effect only about two feet thick.” A geosteering technique that involved the use of logging-while-drilling tools mounted at the bottom of the drill string allowed the team to receive real-time data about the formation.

The work was performed on a highly accelerated schedule, with two drilling rigs operating continuously for about four months to complete all five wells. During this stage, four drilling supervisors from WSP alternated shifts while living at the site. One of their tasks was to ensure that the work crews followed established safety procedures at all times.


Drilling was performed on an accelerated schedule from August through November 2015.

A ‘Christmas Tree’

When drilling was complete, the team began the step-by-step process of completing the wells. This stage involved installation of a complex piece of equipment at the surface to control the flow of gas inside each well. The component is called a “Christmas tree” because the intricate arrangement of valves and gauges resembles a decorated Christmas tree.

The drilling fluids were removed and the wells were allowed to “kick off” and start natural gas flow. The wells were also tested for flow rates to make certain they would perform as expected.

WSP’s extensive experience in reservoir and aquifer storage, hydrocarbon storage in salt and hard rock caverns, and waste disposal through deep injection wells was instrumental in delivering the project successfully.

“Using our expertise to help clients meet their strategic objectives is at the heart of what we do,” Bentley said.

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