Assessing Reservoirs' Viability for Long Term CO2 Sequestration Using Cuttings Volatiles

Abstract

Abstract We present methodology to evaluate long term sequestration viability of CO2 reservoirs using drill cuttings. Cuttings volatile data was obtained from 2 parallel horizontal wells, drilled along the same vertical trajectories, separated by 400 meters in 2019. One horizontal well drilled within 100 meters of a 1994 vertical oil well. The already produced section shows very low CO2 compared to the rest of this lateral and the entire length of the twin lateral. Oil production from the 1994 vertical well reduced reservoir pressure, caused CO2 loss from formation water, and produced CO2 to the surface, lowering reservoir CO2 contents. This example shows cuttings volatiles analyses can detect past CO2 reservoir loss, and is a valuable tool for evaluating long term storage viability of CO2 reservoirs. Another horizontal well, different location and formation, produced about one third of the expected oil. Cuttings volatiles indicate that the heel third of the lateral was oil productive, but that oil in the two thirds of the lateral towards the toe had been lost along a major fault. The CO2 contents in the oil pay zone are normal, but in the oil depleted zone CO2 is very low. Loss of oil from the reservoir along the fault reduced reservoir pressure, resulting in dissolved CO2 loss from formation waters, and CO2 loss along the fault. Cuttings from ten wells from the same limestone formation in a two county area in Oklahoma were analyzed. Nine of the wells show normal CO2 contents. The tenth well drilled across a major fault has 10 to 100 times less CO2 than the other 9 laterals. CO2 in interstitial waters was lost from the reservoir via the fault. Rock Volatiles data indicate the zone drilled by this well is not adequate for long term CO2 sequestration. A two mile high temperature gas horizontal well was analyzed crosses a major fault near the toe. Very high CO2 contents are observed at the fault. The CO2 is generated in a deeper formation and is migrating out through the penetrated formation. Neither formation is adequate for long term CO2 sequestration. Cuttings from two CCS wells drilled by the Kansas Geological Survey were analyzed for cuttings volatiles CCS reservoir viability assessment. Both wells show no signs of CO2 depletion, and are considered by us to be low risk for long term CO2 loss. Rock Volatiles CO2 analyses of cuttings and core is a powerful tool for assessing long term CO2 sequestration viability before new wells are drilled.