The Mississippian oil trend is an expansive carbonate stratigraphic trap producing at shallow depths ranging from 4,500 to 7,000 feet below the surface. The reservoirs lie at the regional Pennsylvanian/Mississippian unconformity, as a result of uplift, alteration and erosion of shallow marine Mississippian carbonates.
The uppermost Mississippian member is a widespread debris-flow deposit formed through a combination of uplift and erosion of the Mississippi Limestone, consisting of varying amounts of weathered chart, limestone and dolomite called the “Mississippi Chat”. The “Mississippi Lime” underlies the chat and also exhibits good reservoir characteristics. The formation was subject to weathering and digenesis and erosion at the regional unconformity. This results in greatly varying reservoir properties both horizontal and vertically. Where the digenesis and weathering have enhanced the reservoir properties, the porosity is generally 15-20 per cent. and can be more than 100 feet thick. Where it has not been enhanced, the porosity is only 4-6 per cent. and has low permeability. This results in lateral discontinuous reservoirs that are ideally developed with horizontal drilling technology.
The horizontal wells drilled in the play have lateral lengths of between 2,500 feet and 5,000 feet and are fracture stimulated in 6-12 stages. The fracture stimulation treatments are not as large as those in the Bakken play or the other unconventional resource plays such as the Eagle Ford. Because of the shallow depths and smaller fracture stimulation treatments, the typical completed well cost ranges from $2.4-$2.9 million. Current drilling times are approximately 17-28 days from spud to total depth.
The active operators in the play have published significant information on their results and expectation on the performance of wells in the play. Sand Ridge currently has over 650,000 acres under lease and the company has completed over 60 wells in the play. They estimate they have over 3,000 potential drilling locations. SandRidge’s published type curve for well performance is 409 Mboe with expected well recoveries ranging from 300,000 to 500,000 boe at an average drill and complete cost of $2.7 million including allocated salt water disposal well costs.
Moyes has analysed the performance of 56 Mississippi Lime horizontal wells that were completed between 2007 and early 2011. The wells had 30 day average initial rates ranging from 60 bopd to 750 bopd. The average estimated oil recovery was 366 Mbo from this sampling of wells.
