The majority of the petroleum engineers agree that fracture pressure gradient is one of the most important items to be considered when designing or drilling a well.
The perception of the importance of the fracture pressure gradient comes from the results of the severe economic losses that the oil industry has faced when dealing with lost circulation related problems. In the worst scenario, these problems can escalate to a blowout due to the reduction of the hydrostatic pressure in the well. In addition, lost circulation problems are likely to occur and become even harder to control if the well is in deepwater.
It is well known that a correct prediction of the fracture pressure gradient minimize drilling problems. However, the methods used by oil industry to perform this task are generally based on equations or methodologies that give questionable results and do not match actual field data.
Fracture pressure gradient methods are generally based either on equation derived from rock mechanics theories or in simplified methods. Although, the first tries to closely represent the rocks underground behavior, they are too complex and call for a number of data that normally are not available. On the other side, the second carries many simplifications and barely represents subsurface conditions. However, the last is simple to use and consequently more popular among drilling personnel. Regardless of the method, a good calibration, in general hard to be accomplished, is always necessary to provide good estimates.
Finally, performing leak off tests (LOT) is usually the procedure carried out by most of the oil companies to establish fracture pressure gradient values for a given area. Once LOT`s are obtained, they are used to calibrate simple equations or will be part of the company database to simply build fracture pressure gradient curves.
The objective of this work is to make a critical examination of the current methods used to estimate fracture pressure gradient. The work also presents simple methodologies based on leak of tests data to estimate fracture pressure gradient for a given area. Results based on actual field data to exemplify the use of the presented methodology will be shown, mostly for deepwater oilfield.