Twelfth Annual CO2 Flooding Conference, Midland, Texas, 6-8 December 2006
David Hughes (david.hughes@senergyltd.com), of Senergy Ltd in Aberdeen and editor of IOR Views, attended the Twelfth Annual CO2 Conference in Midland, Texas. Here he presents his overview of the conference, including his observations on the visit to Oxy Permian Ltd's Denver Unit CO2 flood and processing facilities.
Introduction
This is the third occasion that I have headed for Midland, West Texas in December, having previously attended in 2003 and 2005, and it is an ideal opportunity to catch up with colleagues with real CO2 experience including nowadays a sprinkling of Europeans. This time I was also privileged to be able to make a presentation on North Sea CO2 developments. The CO2 flooding conference is it its twelfth year and the associated carbon management workshop (which on this occasion was held earlier in the week in Houston) is in its fourth year.
In total around 500 delegates registered for the two events – reflecting the growing importance of the issues surrounding CO2. I didn’t attend the workshop but a full report and downloads are posted on the SPE Permian Basin website. The highlight was the luncheon address by the Hon Michael Williams, head of the Texas Railroad Commission. He leads the Texas initiative to obtain FutureGen for the state (Texas has two sites in the final shortlist of four) and is keen to exploit the synergies between clean coal and CO2 EOR.
Field Visit
I arrived in Midland in time for the visit to Oxy Permian’s Wasson field where CO2 flooding has been underway for over 20 years. There were 80 of us in two busses that left downtown Midland for the one and a half hour journey north to Denver City. Once there we congregated in the community centre where Oxy staff outlined the scope of the operations at Wasson and what we were going to see. We also consumed our packed lunches provided earlier.
Figure 1: Map of Oxy Permian operated Wasson San Andres field
Currently 80 Mstb/d oil, 420 MMscf/d gas and 570 Mb/d water are produced from Wasson with 620 MMscf/d gas and 560 Mb/d water injected. Around 200 MMscf/d of CO2 is imported, with the balance from recycling. There are 90 batteries and satellites, 60 compressors, 300 pumps and 1 turbine. 4 gas plants recover NGLs with 3 also recovering CO2 for reinjection. Oil (33°API) initially in place in the 300 ft thick San Andres formation is 4.4 billion stb of which 2 billion has been produced so far. The carbonate formation has a permeability of 1-5 mD in the overlying F (first porosity) zone and 8.5-12 mD in the M (main pay) zone. Oxy operate 4 units in the field, 3 were put on CO2 injection in the mid 1980s and 1 in the 1990s. In total there are 2000 producers and 1200 injectors (vertical wells) on 20 acre spacing, with 100 staff managing the units.
Figure 2: Pumped producer and CO2 injector at Wasson
Some producers flow naturally with some pumped; surface pressure is 150 psia. CO2 injection pressures are 1600-2000 psia and the project is miscible throughout. Injection wells have glass reinforced epoxy coatings (Duoline 20), and corrosion inhibitors are injected into the annulus to protect the carbon steel. The flood is optimised by pattern balancing using a computer program. Slug sizes are 40-100%, averaging in the low 50s%. The incremental recovery is 10-20% OIIP over waterflooding.
Figure 3: Willard gas processing plant at Wasson
As we toured around the Denver Unit in the busses we viewed a CO2 injection well head – in particular we saw the metering arrangements. The same meter is used to measure the CO2 and water rates, with remote operation of the valve which switches between the two fluids. We moved on to see producing wells, test separators, gathering stations and other fluid handling facilities. Finally we toured the Willard gas processing plant, which processes 240 MMscf/d of produced gas. Sulphur is reduced from 2000 ppm to <100 ppm, NGLs are recovered and CO2 is separated from the hydrocarbon gas and conditioned ready for reinjection.
Following a brief comfort break we then made a leisurely return to Midland; altogether a very interesting and constructive day out.
CO2 Conference
The themed sessions on Thursday and Friday morning attracted around 350 attendees.
The integrity and risk management programmes used on their pipeline infrastructure were discussed by Kinder Morgan, improved operational and environmental performance at Monell, Wyoming by the use of state of the art of automation was presented by Anadarko, and EnCana and Fiberspar spoke on the successful deployment of continuous spoolable composite flowlines at Weyburn. Kinder Morgan presented results on their understanding of hydrocarbon gas production during CO2 flooding at SACROC which is important in maximising the value from NGL yields.
In CO2 injection wells, it is important to maintain pressure and rate targets at bottom hole conditions. With reference to SACROC, Kinder Morgan presented methodology to undertake automated rigorous material balance calculations at every injector including improved PVT calculations. ‘Short circuits’ between injectors and producers severely impair the performance of CO2 floods. Oxy described how these may be caused by leaching or fracturing from overinjection and how such features at the Anton Irish unit were remediated using gels.
Denbury presented results from their Little Creek and West Mallalieu Units in Mississippi. Very high incremental oil recoveries (around 17% of oil initially in place) have been obtained from the earlier phases at Little Creek, but this requires significant throughputs of injection gas (300-600% of hydrocarbon pore volume). West Mallalieu is responding in a similar manner. INA described the results a CO2 pilot project in the Ivanić field in Croatia. A nearby industrial source of CO2 has been identified at the Molve gas processing plant and it is hoped to implement fieldwide CO2 injection. The compositional modelling studies for this were described. Apache Canada spoke about a novel pilot project to reinject acid gas (65 mol% CO2, 35 mol% H2S) into a number of pinnacle reefs at the Zama field in northern Alberta. This has the threefold benefit of increasing reserves, eliminating the need to produce free sulphur and reducing CO2 emissions.
Anadarko described the recent performance at the Salt Creek CO2 flood in Wyoming and results and simulations from the Wall Creek I immiscible pilot. Following on from the Thursday visit, Oxy spoke on the performance improvements they are making in the Denver Unit at the Wasson field. This includes adjustments to the WAG strategy (slug size, use of tapered slugs etc), optimisation within the patterns, modifications to the patterns (e.g. convert to inverted nine-spots) and production from the residual oil (transition) zone. Chevron presented studies on the flood expansion at the Vacuum Field in New Mexico. Performance to date has been excellent with quicker than expected response. Areal expansion is planned as well as targeting the transition/residual oil zone.
I was in the honoured position of making the final presentation of the conference. I spoke on the UK Government’s targets to reduce CO2 emissions and how, in part, it is hoped to achieve these by capturing CO2 at fossil fuelled power stations and using it for EOR in North Sea fields. Together with colleagues at Senergy, I have been working as a contractor member of the team at BP designing the proposed CO2 flood in the Miller field. This is part of an integrated project to capture CO2 at a new hydrogen power station at Peterhead in Aberdeenshire, Scotland and export the CO2 to Miller along the old gas export pipeline for EOR and eventual storage. With BP’s permission, I presented an overview of this project (known as DF1) concentrating on the subsurface performance. I was asked questions on the possible effect of compartmentalisation, how significant was override, could horizontal wells be of benefit, can the fate of the CO2 be detected with seismic surveys, what subsidies would the project require and has onshore CO2 disposal been considered in the UK.
My overall impression of the conference is that where there is a relatively economic supply of CO2 available, CO2 flooding is a mature business and today’s high oil prices are promoting ever increasing activity. The challenge now is firstly to get the economics right where CO2 is captured at, and transported from, large industrial sources such as power stations, and secondly to take CO2 flooding offshore. The availability of CO2 credits in cap and trade schemes will help the economics, but the adaptation of offshore facilities and wells to CO2 flooding still represents a considerable challenge. Nevertheless, I look forward to these challenges being overcome and hope to return to Midland again for future conferences.