Post Depositional Alteration of Rock Properties/Surfaces and Implications for Rock-Carbon Dioxide Interactions in the San Juan Basin and Adjacent Areas

As part of the DOE funded San Juan Basin (SJB) CarbonSAFE project seeking to identify faults and potential communication conduits impacting carbon dioxide injected into Jurassic formations, cuttings from four wells forming an approximately 12-mile transect were analyzed using rock volatiles stratigraphy (RVS). RVS was developed by Advanced Hydrocarbon Stratigraphy to provide direct measurements of the volatile compounds in rock samples and rock properties related to the ease with which the 40+ volatile compounds including CO2, various sulfur species, and hydrocarbons measured are released. Legacy cuttings analyzed covered the Jurassic section of each well and typically several thousand feet above and below. Transect wells include a basin well (Kirtland-1, drilled 1961), one effectively on the Hogback monocline (HM) (a fault/fold feature which results in 3-7 thousand feet of "upthrown" vertical displacement; Stephenson-1, drilled 1981), and two wells on the western side of the HM (Ute Dome - Gotor-1, drilled 1981; and Barker Dome - Ute-8, drilled 1975). Data acquired at the time of drilling and RVS data show several matching features providing confidence in the RVS analysis of the legacy unpreserved cuttings. There is evidence in the RVS data of vertical gas migration from the deeper Paleozoic gas zones in wells on the "upthrown" side of the HM. While cuttings from wells on the "upthrown" side of the HM in the transect contain similar quantities of CO2 to the "downthrown" side, these samples have a markedly decreased affinity for CO2 compared to "downthrown" side. The Paleozoic gas zones in the study area are known to contain sour gas rich in sulfur compounds. Linear correlations between the ease at which CO2 is released from samples from wells on the "upthrown" side of the HM and detected sulfur compounds are present. Given sulfides like carbonyl sulfide and carbon disulfide are known to be incompatible with CO2 in gas mixtures due to in situ interactions it is likely that the vertical movement of sour gas has resulted in rock surfaces being modified by these sulfur compounds which in turn modified the affinity of these rocks for CO2 compared to those on the "downthrown" side of the HM. These RVS data, the described mechanism, and the potential implications on CO2 behavior in the surface in the study area will be discussed.