The oil industry has long recognized the need for increasing wellproductivity. To meet this need, a process is being developed whereby theproducing formation permeability is increased by hydraulically fracturing theformation.
The "Hydrafrac" process, as it is now being used, consists of twosteps:
injecting a viscous liquid containing a granular material, such as sand fora propping agent, under high hydraulic pressure to fracture the formation;
causing the viscous liquid to change from a high to a low viscosity so that itmay be readily displaced from the formation.
To date the process has been used in 32 jobs on 23 wells in 7 fields, resulting in a sustained increase in production in 11 wells.
Although explosives, acidizing, and other methods have long been used, therestill exists a need for artificial means of improving the productive ability ofoil and gas wells, particularly for wells which produce from formations whichdo not react readily with acids. This paper discusses the development of ahydraulic fracturing process, "Hydrafrac", which shows distinct promiseof increasing production rates from wells producing from any type of formation.The method is also considered applicable to gas and water injection wells, wells used for solution mining of salts and, with some modification, to waterwells and sulphur wells.
Requirements of Process
In considering such a possible process, it appeared that certain requirementsmust be met. Some of these are as follows:
The hydraulic fluid selected must be sufficiently viscous that it can beinjected into the well at pressure high enough to cause fracturing.
The hydraulic fluid should carry in suspension a propping agent, such assand, so that once a fracture is formed, it will be prevented from closing offand the fracture created will remain to serve as a flow channel for oil andgas.
The fluid should be an oily one rather than a water-base fluid, because thelatter would be harmful to many formations.
After the fracture is made, it is essential that the fracturing fluid bethin enough to flow back out of the well and not stay in place and plug thecrack which it has formed.
Sufficient pump capacity must be available to inject the fluid faster thanit will leak away into the porous rock formation.
In many instances, formation packers must be used to confine the fracture tothe desired level, and to obtain the advantages of multiple fracturing.
As a necessary step in the development of this process, it was deemedadvisable to determine if the Hydrafrac fluids were actually fracturing theformation or whether these special fluids were merely leaking, away into thesurrounding formation. To determine this, a shallow well, 15 feet deep, wasdrilled into a hard sandstone. Casing was set, the plug drilled, and the welldeepened in the conventional manner. A fracturing fluid dyed a bright red wasused to break down the formation. Sand mixed with distinctively colored solidswas injected into the well with the fracturing fluid to prop open any fracturemade in the formation. A simulated gel breaker solution dyed a bright blue wasthen pumped into the well to determine if the gel breaker would follow thefirst solution.