Salt Creep Monitoring in Real Time Drilling Geomechanics: How to Define in Real Time the Mud Weight to Get a Safe Time Window to Drilling, Casing Running and Cementation Job

Abstract

Abstract

Drilling in, and through salt was for a long period avoided due to the challenges that was present when drilling these formations. However, large oil and gas reservoirs are associated with salt structures. In the Gulf of Mexico (GoM) some important oil and gas reservoirs are located below salt bodies. To reach the hydrocarbons section is necessary to drill thick layers of salt with different characteristics. The salt can reach considerable deformation when exposed to the drilling fluid. This deformation is function of the magnitude of in-situ stresses, mud density, exposure time, temperature and the mineralogic composition. This behavior is known as salt creep.

The real time salt creep analysis can describe the wellbore diameter in function of drilling time. The higher mobility will faster to reduce the wellbore diameter. One example was a well in the Campos Basin in Brazil where the closure velocity was obtained in the order of 0.05 inches per hour in Halite. This rate of deformation depends on the conditions under which the rock is submitted. High mobility can generate non-productive times such as: back reaming, stuck pipe, well deviation and a catastrophic lost hole.

This paper presents a new monitoring methodology that compute the wellbore diameter in function of exposure time while drilling, using an analytical model, calibrated with offset wells data. The specialist updated a geomechanical model, considering the lithology and mineralogic composition of the salt section using the LWD data and drilling parameters. Profiles of hole diameters and forecast from the actual time to the end of section are available in real time. The information allow the drilling engineers adjust the planned mud weight to reduce risks of stuck pipe and ensure a successful casing running and cementing operations.

AAPG Datapages/Search and Discovery Article #90260 © 2016 AAPG/SEG International Conference & Exhibition, Cancun, Mexico, September 6-9, 2016