Acid Gas Injection in the Permian Basin: Recent Case Studies from Southeast New Mexico

Acid gas injection is becoming an increasingly popular choice for the disposal of gas processing wastes and CO₂ sequestration in the Permian Basin of southeastern New Mexico. Five AGIs have been brought on‐line and several additional projects have been successfully permitted in the last few years. The first AGI well in northwestern New Mexico (San Juan Basin) has been successfully permitted and is scheduled for completion by year end.

Sour gas containing high H₂S and CO₂ produced here has traditionally been treated to remove H₂S and CO₂ from the field gas. A sulfur recovery unit (SRU) is then used to convert the H₂S to sulfur and discharge the CO₂ to the atmosphere. AGI has been proven as a cost‐effective and environmentallybeneficial alternative to traditional treatment by:

• permanently sequestering both CO₂ and H₂S geologically
• eliminating costly SRUs
• increasing plant capacity
• reducing air emissions and obtaining carbon credits

While the Permian Basin has an abundance of deep saline aquifers suitable for injection reservoirs, site selection is complicated by extensive active oil and gas production. In this paper we explore reservoir selection and characterization, permitting, design and completion of AGI wells in southeastern New Mexico using examples of wells we have successfully completed. We will also discuss ongoing efforts to register these projects as permanent CO2 sequestration sites and obtain associated carbon credits.

The Jal 3 AGI #1was completed in December 2008 to increase plant capacity, sequester CO2 and eventually eliminate an aging SRU. It also replaced an existing Class II disposal well. This AGI system is designed to handle 1.5‐5 MMSCFD of treated acid gas (20% H₂S and 78% CO₂) and plant wastewater at about 880 psi. Injection occurs below ~4450 feet into the San Andres limestone with porosity up to 15%. This reservoir is contained between a low permeability zone (<=0.1 mD permeability) in the upper San Andres/ Grayburg dolomite and a layer of anhydrite in the lower San Andres.

Linam AGI #1. The Linam AGI was designed to replace the SRU, and reduce air emissions by eliminating excess flaring at the plant. Since there was no suitable reservoir located at the plant site, the well was drilled 1.5 miles away and connected to the plant by a pipeline. The AGI well was completed in December 2007, commenced injection in late 2009 and is currently injecting 2.5-3.5 MMSCFD of dry gas (25% H₂S and 75% CO₂) at about 1100-1300 psi. The well is injecting below ~8700 feet down into Lower Bone Springs Formation (Wolfcamp) carbonate, the lower of two potential injection zones. This unit is capped by the Clear Fork formation that includes tidal deposits and evaporites.