From liability to cost effective data gathering opportunity The revival of a twenty year old exploration well
By Edwin Quint, Candy Beck Brake, John Bickley, Bud Johnston and Paul Huckabee Shell Americas
Commercial production from micro-Darcy reservoirs has only been established recently as a result of advances in hydraulic fracture technology. Little is known about reservoir pressures, drainage areas and recovery efficiencies in these ultra tight reservoirs all of which impact optimal field development and well spacing. Improperly developing a field based on incorrect assumptions about drainage area can be costly.
The Pinedale anticline in the Green River Basin, Wyoming, is an example of this type of reservoir. The producing formation is a thick section of fluvially deposited Lance formation that has over 5000 feet of gross thickness but only an average permeability of 5 micro-Darcy. Pressures vary considerably from the top of the producing formation to the base. Unfortunately direct accurate pressure measurements have been difficult to obtain with the standard wireline tools due to the extremely low permeability.
Many wells were drilled into the Pinedale gas accumulation prior to establishing commercial production. These wells were viewed as a liability given the need to plug them but one of the wells was given a ?second life? as pressure monitor well and will now provide data for years even after its abandonment. To address the spacing issue other operators have drilled closely spaced wells to monitor production interference between producing wells. However, in an area with complex geology it may take years to see interference and it will be difficult to distinguish it from compartmentalization. Pressure changes between wells would occur much sooner and would be more conclusive. However, most operators are reluctant to drill new wells that cannot be put on production immediately. Therefore the old wells provide a unique cost effective opportunity for long term pressure monitoring.
Instead of abandoning an old well with a few plugs an abandonment with multiple permanent plugs with pressure gauges below them and a wireless communication system can be used to transmit pressure data to the surface for years after abandonment. In addition to giving indications of depletion, these gauges provided the first reliable initial pressure data for Pinedale.