Hydraulic Fracturing "fracing" and some technical notes on how it is used

I comment again, I want people come to understand what Hydraulic Fracturing "fracing" is and how it is used. It is in simplest form, a method to stimulate the well. In the Industry it is just that, Well Stimulation. The professionals who design these plans to create pathways for the flow of Hydrocarbons from the reservoir to the wellbore concern themselves with permeability and proppant among other factors that ultimately define deliverability of trapped gas. By using Stokes' law, {which defines four parameters that influence proppant settling velocity in a column of water: fluid specific gravity, fluid viscosity, proppant size and proppant specific gravity} the natural gas people decide the volume of proppant designed into a facturing treatment. One way to minimize fracture stimulation costs is to minimize frac fluid viscosity. Although trade offs occur if you take this route, everything requires study, there isn't a templete, one size fits all. In Stokes' law, cutting the particle diameter in half reduces the settling rate by a factor of four. This attribute is often used when choosing smaller proppant sizes in facturing treatments. However, proppant size is also proportional to proppant pack conductivity. So proppant size reduction for transport purposes must be weighed versus the need for fracture conductivity.

What is proppant and why discuss it? We know sand and other items are mixed with water and injected, that is proppant. The official version is: Proppant: Sized particles mixed with fracturing fluid to hold fractures open after a hydraulic fracturing treatment. In addition to naturally occurring sand grains, man-made or specially engineered proppants, such as resin-coated sand or high-strength ceramic materials like sintered bauxite, may also be used. Proppant materials are carefully sorted for size and sphericity to provide an efficient conduit for production of fluid from the reservoir to the wellbore.

Fracture design models guide stimulation optimization by comparing treatment size versus fracture half-length and the resulting productivity predicted for a particular design.

For low-permeability reservoirs it is commonly accepted that fracture length dominates stimulation effectiveness. However, this is only partially true because any fracture length or height created without enough residual conductivity to be effective (i.e. unpropped) is a waste of the fluid that was pumped for its creation. So the return on frac investment was poor, a loss.

The water that flows back and must be treated also doesn't have a magic pill for set answer, each site is different. A well using a partial monolayer proppant like Lite Prop will have three times higher conductivity at 4000 psi closure than lbs of sand pack and 30 times more conductivity per lbs of conventional proppant in place.

Does length or size matter? It sure does when the producers create the game plan. The longer the transport distance the larger propped fracture area and stimulation efficiency. Many factors effect "fracing" and it is only fair for some of us to glimpse inside the mind of those production engineers. Also, from a layman, this does effect the amount of water used on each well.

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Comment by Gene Water Recycler aka.PPC on June 17, 2010 at 7:20am

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