Earthquakes are caused by a sudden release of energy in the earth’s crust when two sections of the crust slip past each other.The size of an earthquake is determined by the Richter magnitude scale, which ranges from 0-10. Earthquakes are sometimes classified as:
● Micro Earthquakes. Earthquakes that register less than 2.0 on the Richter scale are called micro earthquakes and are typically not felt at the surface. Micro earthquakes are so frequent that it is estimated that they may be continually occurring or that there are several million that occur each year.
● Minor Earthquakes: Earthquakes that register 2.1 to 2.9 on the Richter scale are called minor earthquakes and occur over one million times per year. Minor earthquakes can be felt slightly by some people, but cause no damage to buildings.
● Minor Earthquakes: Earthquakes that register between 3.0-3.9 on the Richter scale are also called minor earthquakes and are often felt by people on the surface, but very rarely cause damage to buildings. Minor earthquakes between 3.0-3.9 occur over 100,000 times per year.
Hydraulic Fracturing, and Disposal Wells and Earthquakes
Hydraulic fracturing is a well stimulation technique in which rock is fractured when a high-pressure fluid is injected into a well bore to create fractures in the deep rock formations where oil or gas is held in pores of the rock. Fracturing is usually necessary to obtain adequate flow rates in shale gas, tight gas/oil, and coal seam gas wells. Hydraulic fracturing was first performed in 1947 and over one million frac jobs have been performed within the United States. Frac engineers design frac jobs by evaluating the formation and determining the proper amount of fluid and pressure needed to fracture the reservoir rock in the zone of interest. The fluids used for fracking are recovered and disposed of by injection into a disposal well.
The early studies in this area are indicating that drilling and fracking may be correlated with earthquakes. You can access those studies here, here and here.
It remains to be seen what impact this information will have on exploration and drilling activity in Texas long term.