Technology Update: Well Stimulation/Completion Using High Explosives
Authors: JPT staff _ 
Published: February 2015

The objective of using high explosives in well stimulation is to increase the effective drainage area at reduced cost. One form of explosive stimulation uses dilatant technology, in which rock-volume is permanently changed through the use of explosives. Porosity can be increased 200% or more as a result of controlled microfracturing/cracking.

Introduced by Sigor Corp. in 2004, the SWT orpedo, a dilatant explosive technology (Fig. 1), is based on rock behavior under overbalanced dynamic stress, when rock fails at 5% of its strength and dilatancy/shearing is triggered as far as 60 ft from the wellbore.

Field applications of the technique have shown that extensive microfractures increase yield as much as five-fold in oil wells and seven-fold in gas wells; water production is doubled in irrigation wells. Stimulation of potentially productive intervals in which rock properties are known and hydrocarbons in place was 96% effective.

The dilatant method requires a relatively small amount of high explosive compared to the amount required for common explosive techniques/propellant tools. It can supplement acidizing and/or be used ahead of an acid job to increase acid/rock contact, and it is competitive with the hydraulic-fracturing method (designed to extend a fracture up to 150 ft in low-permeability sands). The dilatant method also can be compared against the use of nitrogen in shale when the tool is detonated in formation water or in diesel.

The technology was applied in the Appalachian basin with JP Oil and BJ Oil and Gas in cased gas wells and openhole wells, respectively. The result of the stimulation effort for JP Oil in Medina sands was an increase in gas production from a maximum of 7 to 50 Mcf/D. Also in the Appalachian basin, this technique was used by BJ Oil and Gas to increase production in an openhole well that had been producing for 40 years before treatment. Production increased from 4 to 20 BOPD and from 20 to 53 Mcf/D of gas. The increase was sustained for 6 months and then declined to 12 B/D (Fig. 2). Coalbed-methane wells in the Powder River basin were stimulated using dilatant technology, and Williams Production saw an increase in beneficial water production from 76 to 128 B/D.

Dilatant technology has been successfully applied in the following formation types:Strong, medium, and weak sandstones.Strong, weak, and dense limestones.Dolomites.Strong and medium shales.Strong coal.Granite.

Increasing Drainage Area

Extremely high pressure on an average of 1 million psi created by high explosives usually lasts for a few microseconds, often causing rock compaction, but extending time for such high pressure up to 3 milliseconds will initiate shearing (all active forces are compressive), and allow microfractures to propagate as far as 120 times the radius of the explosives being used. For instance, a 3½-in.-diameter tool containing explosives will shear the rock as far as 30 to 35 ft from the wellbore. The drainage area will equal the area of an ellipse horizontally 70 to 90 ft and vertically 50 to 65 ft in size. This drainage area often exceeds the effective drainage area from a 150-ft-long fracture created by a hydraulic- or sand-fracturing method.