Mellott Ranch field is located in Section 28 of Township 53N and Range 67W Wyoming and is currently operated by Hilcorp. The Minnelusa A and B reservoirs have a total pore volume of 26,762 Mbbls with an OOIP of 20,686 MSTBO. The porosity is 20.5% and permeability ranges from about 100 mD to over 1,300 mD. It produces a 22o API gravity crude oil with a viscosity of 23 cp. The portion of Mellott Ranch ASP flooded is the northeast portion of the field. Wells 22-11 and 32-11 served as injection wells with 34-02, 41-11, and 12-11H being the production wells. No withdrawal occurred to the southwest within the same sand pod. The 15-11 and 43-10A wells in the most southern pod B Sand were production wells with water injection into the 34-10. Wells 12-11, 22-11, 43-10, 44-10, 34X-10 and 14-11 were either converted to disposal wells into the Minnelusa C sand or plugged at the time of the pilot. Water was injected into the most southern pod because wells 15-11, 43-10A, and 34-10A had comingled production and injection with the Minnelusa A sand above the B sand. Mellott Ranch Minnelusa B net pay isopach is shown to the left. Swept or floodable pore volume between the 21-11 and 32-11 injection wells and the 34-02, 41-11, and 12-11H production wells is 12,200 Mbbls. Original oil in place is 9,860 Mbbls or 80.8% oil saturation. Bo is 1.02.
Initial production from the swept area was from the 32-11 in August 1961.Within the next six months, wells 34-02, 41-11, and 21-11 were drilled and placed on production.Primary oil recovery from the flooded pore volume was determined as 50% of the production from 32-11, 34-02, 41-11, and 21-11. Primary production from the swept area was 205,744 bbls or 2.1% OOIP. Water injection began in wells 12-11 and 23-11 in December 1965.Response to water flood is evident beginning August 1966 in both the 32-11 and 21-11.Well 21-11 was plugged in 1973 due to mechanical problems with the last injection occurring in December 1972.Injection continued into 12-11 until July 2000 when it was deepened to the Minnelusa C and used as a disposal well.Wells 32-11 and 21-11 were produced until April 1989 and December 1968 respectively when they reached an uneconomic oil cut.Well 21-11 was converted to water injection in August 1984 and Well 32-11 in January 1990.Well 12-11H was drilled and placed on production in January 1998.Waterflooding continued until ASP solution was started in August 2000.Waterflood production from the swept area was 3,628 MSTB or 36.8% OOIP for a total primary plus waterflood of 3,833 MSTB or 38.8% OOIP at an oil cut of 5.3%.Stock tank oil saturation in the swept area is approximately 49% PV at the end of the waterflood.A final well, 44-2 was drilled in the SESE of section 2 and is considered out of the ASP flood swept area.
Westport Oil and Gas took control of the field in the early 1990s and initiated the study to implement a chemical flood in 1999.A laboratory ASP design program was performed with radial coreflood results for the field injected solution shown in the figure above.In August of 2000 when oil cut was about 5.3% injection of an ASP solution consisting of 1.0% NaOH + 0.1% ORS-46HF + 1,300 mg/L Alcoflood 1275A began in two wells.Injection of ASP continued until June of 2004.Polymer drive solution was injected from June 2004 to October 2006.A total of 0.301 pore volume of ASP solution was injected into the swept area and 0.200 pore volumes of polymer drive.The injection rate for the swept volume is relatively low averaging about 0.07 pore volume per year for both the ASP and polymer drive solutions injection.
This compares with 0.08 pore volume per year for the preceding 6 years of water injection.Oil cut increased to a peak of 13.9% with 681,257 bbls produced from August 2000 through November 2008.Well 41-11 responded best to ASP solution injection with oil cuts increasing from 9.6% to a peak of 35.8%with the total oil production from August 2000 to November 2008 being 142,797 bbls.The figure above on the left depicts the 41-11 production and the figure above on the right depicts the swept area production. The figure below shows the Mellott Ranch production compared to the Cambridge Field and the average of eight Minnelusa waterfloods.Note that Mellott Ranch waterflood performance is a typical Minneulsa waterflood.
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