Options of multiple drilling in the Mako Trough

Tibor Balázs, Zsolt Feczkó, Gary Lavold (TXM)

As some of you may know, Falcon/TXM has been actively exploring the options of bringing the basin-centered gas accumulation (BCGA) in the Makó Trough under production. Over the past few years, Falcon/TXM has taken strides toward utilizing this significant prospective gas reserve. The years following the development of the play have been dedicated to locating and drilling 4 wells on the flanks and 3 on the basin centre based on 3D seismic survey data. The data obtained from these wells in turn have been used to refine the model set up on the basis of the 2D and 3D survey results. Drilling these wells has reconfirmed a fact that had been widely known for some time: the reluctance of the Makó Trough to give up its riches.

In order to reach the BCGA cells, the wells need to penetrate to great depths of 3500 to 5500 m. Drilled in high-temperature, overpressured rock cells that are also compacted and have poor permeability and porosity to boot, the wells will not be capable of economically feasible production until after hydraulic fracturing has been performed. Mainly due to the poor permeability, BCGA wells have a drainage area of a rather small radius compared to conventional wells, albeit one that is much longer vertically.

While these challenges clearly entail financial consequences, the economy of production will to a large extent depend on well pacing. As to increasing that spacing, the obvious solution is to drill several wells from the same single site – a process known as multi-pad drilling.

Many modern drilling rigs today come capable of being skidded from cellar to cellar using a simple hydraulic system even with a drill pipe stand in the mast, and those that do not can be retrofitted for that capability with relative ease.

The ideal distance between the cellars in the same common concrete basement is 4 to 6 meters. In the simplest configuration, which is the linear one, the substructure and the mast with the stand can be skidded from one cellar to the next, in hours rather than days, while everything else – the tank system, pumps, generators etc. – remains in place. It can be said, therefore, that the number of wells that can be drilled in a linear multi-pad configuration without rigging up and down will be determined, in addition to the well pacing, by the pressure loss in the hoses and lines and the maximum length of the flow line. This yields 4 to 6 wells that can be drilled with a single rig up/rig down. A four-well cluster already represents significant economy of time and thus significant savings.

The costs can be further reduced by regarding all the wells drilled from the same spot as a single drainage area, and by planning stimulation, fracking and other jobs on a rolling schedule so they can proceed from well to well without interruption or loss of time. One potential benefit of this method is keeping the rig drilling away while fracking or even production testing is under way on another well that has already been completed.