New Blasting Methods Improve Oil Recovery
Authors: Spencer A.M. , Dysart G.R. , Anderson A.L. 
Published: December 2007

Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussions may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

While explosives have been used in the oil fields almost from the beginning of oil production in Pennsylvania, new explosives and more production in Pennsylvania, new explosives and more efficient placement techniques have revitalized interest in this old method of stimulation. We have examples of these new processes ranging from huge 80,000,000-pound equivalent of TNT at Project Rulison to liquids which detonate in thin fracture sections. The newly developed slurry explosives, the most powerful chemical explosives presently commercially available, have been adapted to oil field usage. Placement, initiation an-d containment techniques will be described. Test data from many dry hole experiments will be given. A fracture distance propagation equation was developed by correlating propagation equation was developed by correlating this data and the work of others and by the use of elementary rock mechanics. Finally, the results of field applications in Texas, New Mexico and Oklahoma will be given.

Introduction

Interest was heightened in explosive fracturing of oil and gas wells by the two recent nuclear explosions in right gas formations. Project Gasbuggy and Project Rulison were Project Gasbuggy and Project Rulison were efforts to unlock tight gas reservoirs with enormous energies poured into the formation. Much has been learned in these multi-million dollar tests arid the industry awaits the initial results of Project Rulison which should be sufficiently "cool" radioactively to be entered in March 1970. It is known that fractures were treated hundreds of feet from the site of the nuclear device and that these high energy sources can be totally contained.

These two very energetic explosions are only a part of the recent efforts to stimulate wells. with explosives. The Bureau of Mines has done extensive testing in shallow rock formations and has also participated in joint testing programs with an oil company. Some of the old nitro shooting still continues, provided the well is neither to deep nor to hot. provided the well is neither to deep nor to hot. Other experiments have been conducted with liquid explosives and slurry blasting agents primarily in shallow wells. primarily in shallow wells. This interest in explosive stimulation arises primarily from the non-directed fracturing which occurs upon detonation. This action is considerably different than that which occurs during hydraulic fracturing. Hydraulic fracturing tends to propagate the fracture along an existing plan of weakness in the rock. This leaves a rather large area which drains inefficiently (or not at all) simply because part of the formation has been untouched by part of the formation has been untouched by the stimulation treatment and the attendant pressure drop caused by producing hydrocarbons pressure drop caused by producing hydrocarbons into a fracture. This situation is diagrammed in Figure 1 where we are looking down on the bore hole with the fracture radiating along a line outward from the bore hole. The well fluids (or gas) flow into the fracture and thence to the borehole and surface. The drainage area has been increased along the plane of weakness in this type formation, however a major area is still relatively untouched. What is desired is that the formation will drain and feed the bore hole in a uniform manner. This situation is diagrammed in Figure 2 where a series of unoriented fractures intersect the wellbore.