The Unconventional Well Factory

There are two broad sources from which the gas we use is produced – conventional and unconventional resources. Conventional gas comes from large pockets of porous rock in which it is trapped. The most common types of conventional gas are:

• Tight gas – mostly found trapped in limestone or sandstone formations with relatively low permeability
• Shale gas – mostly found trapped in layers of sedimentary shale rocks
• Coal seam gas – gas absorbed on the surface of relatively shallow coal seams

The formations unconventional gas is produced from typically have low permeability. Due to the low permeability the drainage radius (the no flow boundary) is much shorter for an unconventional well compared to a conventional well. This means (all else equal) that a well in a conventional field has a higher flow rate than a well in an unconventional field.

To get commercial quantities of gas, many more wells need to be drilled in an unconventional field than a conventional field (wells are drilled with closer spacing to recover the volume of gas stored in the reservoir). For example in a large conventional reservoir there may be fewer than 10 wells (yes there can be many wells deviating from a single well head but lets keep it simple) whereas a conventional reservoir may have hundreds or even thousands of wells spaced across it.

The high volume and frequent drilling of unconventional wells presents the question: do you drill 1 well 1000 times or 1000 wells 1 time? This is an important distinction to make because the costs in drilling these wells is controlled by the time required to drill and complete the well. By treating this mass of wells as a production line the cost to drill and complete wells can be drastically reduced.

Creating an unconventional gas well production line can be done by standardising parts and procedures across all wells as well as automating any dynamic and ongoing decision making required. In coal seam gas one piece of dynamic decision making required is to design the well completion to expose the coals and isolate the non-coal regions to prevent the well producing solids.

A popular completion method to serve this purpose is open-hole slotted liner completions. In this type of completion, the drilling team must determine the optimal coals to package into exposed regions and the optimal casing design to reduce completion time while achieving key well design specifications. Learn more about this and how Endla’s product AlphaTally is helping the coal seam gas companies reduce their drilling cost by taking another step towards a single production line well factory here.