Changes

Different types of rocks have different physical properties and contain different fluids: oil, natural gas and water. The location, size and design of the rock’s existing fractures, density and variations in subsurface pressures also affect the hydraulic fracturing operation, so all of these factors must be considered for every type of rock that will be hydraulically stimulated.

Different types of rocks have different physical properties and contain different fluids: oil, natural gas and water. The location, size and design of the rock’s existing fractures, density and variations in subsurface pressures also affect the hydraulic fracturing operation, so all of these factors must be considered for every type of rock that will be hydraulically stimulated.

   

   

For most oil and gas wells, the force of gravity on the rock generally determines the vertical pressure at any depth. Vertical pressure on the rock increases as you go deeper, just as water pressure increases as you go deeper in the ocean.

For most oil and gas wells, the force of [[gravity]] on the rock generally determines the vertical pressure at any depth. Vertical pressure on the rock increases as you go deeper, just as water pressure increases as you go deeper in the ocean.

   

   

An additional complication is that rocks are deposited in basins and are not all horizontal – and they are pushed as the continents shift. The vertical pressure always generates the largest stress on a rock; the horizontal stresses on a rock will control the lateral spreading of the hydraulic fractures. Fractures tend to form in the direction of the least stress, which is generally horizontal.  

An additional complication is that rocks are deposited in basins and are not all horizontal – and they are pushed as the continents shift. The vertical pressure always generates the largest stress on a rock; the horizontal stresses on a rock will control the lateral spreading of the hydraulic fractures. Fractures tend to form in the direction of the least stress, which is generally horizontal.