What is a Frac Job?

I've had several posts on frac jobs of oil and gas wells.  It is actually a complex process and there is a lot of chemistry that goes into the design of a frac.  Each frac is specific to the well and its properties such as pressure, temperature, pH level, lithology, and others.  Thousands of gallons of water are used for frac jobs and very miniscule amounts of chemicals (.004% per thousand gallons of water) can completely alter the properties of the fluid .  The idea of a fracture job is to create a super highway for hydrocarbons to travel into the producing wellbore.  The shape charge perforations which I explained in earlier posts are the first step to the job.  The frac fluid is pumped into the wellbore and uses a crosslinker to suspend sand proppant and carry it into the perforation.  The crosslinker can vary from fluid to a solid composition such as one that Schlumberger uses.  The crosslinker can be modified to delay the conversion of the fluid into gel so optimization of sand suspension and placement can be achieved.  The type of sand used depends on the pressure encountered at the fracture.  Some sand can be crushed if the pressure is too great and man made ceramics can be used in these cases.  Once the gel has carried the sand into the fractures to create a super hydrocarbon highway, a breaker is added to return the fluid system to a less viscous state.  The fluid is pumped back to surface returning the majority of chemicals and additives in the fluid system to tanks on surface while leaving the proppant to maintain the fracture open.  This method of stimulating a well has become routine for nearly every well drilled in order to enhance production.  This method is the technology driving these tight gas sands and shale research for economic production of new reservoirs being discovered today.  Multiple zone fractures are highly common and a 3D image is seen below to monitor the effectiveness of a hydraulic fracture stimulation job.  Each color represents a different zone.

A frac job also requires a lot of hydraulic horsepower.  This is achieved by connecting several pump trucks ranging from 1000 hp to 3000 hp each to a unit called missel located in between the group of all the trucks.