Potential of Microbial Enhanced Oil Recovery in Selected Australian Reservoirs
Engineering Honours Degree, 2006
University of Adelaide
Microbial Enhanced Oil Recovery has potential in Australia and in particular in Santos Ltd’s fields. The possible MEOR fields reside in the Cooper / Eromanga Basin. The geothermal gradient for this basin is high and therefore the applicable fields are quite shallow. They are typically at a depth of less than 4200 ft. Thus, temperature is the most limiting factor for MEOR in onshore Australia. Offshore wells were generally found to be too deep and also of too high a temperature. The microbial limit of 200˚F restricts the number of fields applicable for this technology.
The possible Santos Ltd fields are mostly a mix of undeveloped and primary recovery fields. This means that recommendations made are not currently applicable for most of the reservoirs. The recommendations made are for the future when full development has occurred and tertiary recovery is more appropriate. However, there are fields and formations where MEOR could be instigated at this time.
The Jena, Alwyn, Limestone Creek, Biala and Ulandi Fields (JALBU Complex) present the opportunity for waterflood improvement in the Murta formation. This is subject to the results of a pilot waterflood in the Jena Field. Due to the high permeability streak in the Murta, after waterflooding there is also the possibility of permeability modification. Blocking the high permeability zone using microbial plugging will divert the waterflood into the lower permeability zones unlocking additional oil. These applications should be carried out after the initial field waterflood is performed.
The Kobari Field has yet to undergo any field development and therefore it is difficult to propose any MEOR applications. However, due to the similarity of the Murta in this formation to the JALBU Complex, waterflood enhancement may be a possibility in the future.
The Thungo Field has production from the Murta. The Murta in this field is similar to the JALBU so there is the possibility of adding microbes to a waterflood, followed by blocking high permeability areas using microbial mechanisms to increase recovery.
The Namur Formation in the Biala Field, the Namur / McKinlay Formation in the Tantanna, and the McKinlay Formation in the Jena and Ulandi Fields offer MEOR opportunities. Having reasonably strong water drives allows injection in peripheral wells which have watered out to enhance the displacement of oil by water to the remaining production wells. There are wells in the Ulandi and Tantanna Fields which have already watered out and are ready for microbial injection. The Biala Namur and Jena McKinlay have yet to reach uneconomical water cuts. In the Jena Field there also exists an opportunity to apply stimulation using microbial sweep improvement to continue production on crestal oil pools that have watered out.
In the Nungeroo and Mooliampah Fields, there is the opportunity to stimulate the low rate wells using microbes to re-initiate or increase production.
In the Tintaburra and Toobunyah Fields, the bottom water drive does not allow any waterflood or aquifer improvement. Therefore, stimulation microbe species can be injected into wells that have watered out. After a shut-in period the wells can be reopened and a small increase in oil production should be noticed.
Prior to implementing MEOR in any of these fields, some additional steps and research needs to be undertaken.
Temperature is a crucial environmental factor for microbial survival and activity. Therefore, if possible, the temperature of the relevant formations should be checked to verify that the temperature is below the limit of 200˚F.
Basic laboratory testing such as bacteria compatibility, microbial transport and plugging tests need to be carried out to confirm microbial injection is appropriate for the identified situations. The applications of MEOR in Santos Ltd are in smaller oil fields and so costs should be minimised. More extensive and expensive laboratory testing such as MRI and X-Ray CT should therefore be avoided.
The costs of implementation need to be further examined. Laboratory testing and microbe purchase are two initial costs. Field equipment is not extensive but is specialised, so the costs need to be closely examined and estimated. The cost of a mobile MEOR unit is the main equipment cost. For injection into the formation, a further cost may be the conversion of a production well into an injection well. Lastly, it is likely an experienced MEOR person or microbiologist will need to be hired to assist in on-site microbe inoculation, growth and injection.
CSIRO is currently commencing research into the subject of MEOR. It is likely that they are looking to form industry links to further their field research into the area. A relationship with the CSIRO should be investigated.