ACID GAS INJECTION IN THE PERMIAN AND SAN JUAN BASINS: THREE RECENT CASE STUDIES FROM NEW MEXICO

Acid gas injection is an increasingly popular choice for disposal of gas processing wastes and CO2 sequestration. Over the last 5 years, we have brought six AGIs online and additional projects have been successfully permitted. The first AGI well in the San Juan Basin was successfully completed last year. Sour gas containing high H2S and CO2 has traditionally been treated to remove H2S and CO2 from the field gas using a sulfur recovery unit (SRU) which discharges the CO2 to the atmosphere. AGI has been proven as a cost-effective and environmentally-beneficial alternative to traditional treatment by:

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

This paper explores the geologic process of reservoir selection and characterization, permitting, design and completion of AGI wells using examples of wells we have successfully completed.

The Jal 3 AGI was completed in December 2008 to increase plant capacity, sequester CO2 and eliminate the SRU. This AGI system is designed to handle 1.5-5 MMCFD 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 in the upper San Andres/Grayburg dolomite and anhydrite in the lower San Andres.

The Linam AGI was designed to replace an SRU and reduce flaring at the plant. It commenced injection in late 2009 and is currently injecting 2.5-3.5 MMCFD of dry gas (25% H2S and 75% CO2) at about 1100-1300 psi. The reservoir is ~8700 feet deep in the carbonates of the Lower Bone Springs Formation. This unit is capped by the Clear Fork Formation,a tidal-evaporite sequence.

The Pathfinder AGI #1 was also designed to replace an aging SRU, sequester CO2 and eliminate flaring. A suitable reservoir to sequester approximately 4 MMCFD of treated acid gas with a composition of 20% H2S and 78 % CO2 was located in the Entrada Sandstone with 24 feet of net porosity between 6350 and 6490 feet depth. This well was completed in November, 2010 and 160’ of core was taken from the cap rock and reservoir. The reservoir is an aeolian sandstone capped by tight carbonates and mudstones. Geolex is currently designing and permitting 3 additional wells in the Permian Basin and in southeast Texas.