CO2 Enhanced Gas Recovery Studied for an Example Gas Reservoir

Abstract

Abstract In the wake of the Kyoto protocol, CO2 emission reduction to control the level of CO2 in the atmosphere has become an important goal. One possibility of reducing greenhouse gas emission is to separate and inject CO2 from gas fired power plants into gas fields. To investigate the effects of CO2 injection on methane recovery, five different CO2 injection strategies were investigated for an example gas reservoir. The injection scenarios included installation of a Zero Emission Power Plant (ZEPP) at surface, supplying the reservoir with a constant CO2 rate over 25 years. Installation of a ZEPP enabled using a lower tubing head pressure than for gas delivery to the gas distribution grid resulting in accelerated methane production. For most of the cases investigated, the cumulative methane production was increased as well. CO2 breakthrough occurred between 3 and 15 years. The CO2 which was produced in the production wells was fed into the ZEPP and re-injected with the newly generated CO2. The highest incremental gas recovery was obtained for the case of conventional depletion of the gas reservoir until abandonment and subsequently injection of CO2, leading to enhanced gas recovery. The maximum incremental gas recovery was about 10% of Gas Initially In Place (GIIP). For the case of injection of CO2 early in the life of the gas field, the methane recovery was decreased compared with conventional gas production by depletion. Introduction In the wake of the Kyoto protocol, CO2 emissions reduction to control the level of CO2 in the atmosphere has become an important goal. Due to the lack of suitable alternatives for large-scale energy generation in the short- and medium-term, solutions for reducing CO2 emissions from burning hydrocarbons are intensively investigated. One possible solution is to sequester CO2 in the subsurface. Hydrocarbon reservoirs have a cap-rock which was sealing in geological history for geological times and are prime candidates for sequestration of CO2. CO2 injection into oil reservoirs has been extensively investigated and is commercially pursued, in particular in the USA. Current oil production from fields in which CO2 is injected is about 300,000 bbl/day. A small but significant fraction of the CO2 used for Enhanced Oil Recovery (EOR) in the USA is coming from anthropogenic sources. Currently, a number of feasibility studies are being performed to investigate the use of CO2 generated by power plants in EOR projects. CO2 injection into coalbed methane reservoirs is extensively being studied as well. Numerous laboratory experiments have been performed. In the last few years, field tests of this technology were conducted. CO2 enhanced gas recovery (EGR) has not been studies as extensively. The reason might be the already high recovery of gas for conventional depletion of reservoirs. Due to the fact that in some countries huge gas reserves exist and only a limited number of oil fields, sequestration of CO2 into gas fields might be an attractive option. In the study reported here, integrated power plants with CO2 separation (Zero Emission Power Plants - ZEPP) in combination with a number of different injection schemes into a gas reservoir were evaluated. For an example scheme of a power plant and gas field see Figure 1. To simulate the effects of CO2 injection on methane recovery, an example gas reservoir was chosen. In the following paragraph, the key properties of the field are presented. Then, simulation results for different injection strategies will be given.