RIASSUNTO
Abstract
It is well known that monitoring cuttings allows drilling engineers to take remedial solutions to control wellbore instability while drilling. Unfortunately, just the cuttings volume interpretation can be easily misunderstood and borehole instability can become unmanageable. Besides, most of the projects are drilled in very complex areas. If too much time elapses after wellbore instability begins occurring and the decision to modify mud density is taken too late, the final situation can be stuck pipe, fishing operations and finally the always expensive side track operations.
This paper presents a real example of geomechanical integration with drilling operations, not only during planning, but during the drilling stage, in an area with huge geological and geomechanical uncertainties.
During the planning stage, geomechanical and wellbore stability models were defined based on data analysis and pore pressure, mechanical properties, and stress profile predictions. As a result of the planning, the mud weight window, mud properties and formulations were defined as well as BHAs and casing points. While drilling, borehole conditions were monitored to optimize a ""planning-while-drilling?? wellbore stability model according to the changing wellbore circumstances. This methodology can allow all the well construction objectives to be achieved.
Introduction
Commonly, the mud weight window is designed by using pore and fracture pressures as the lower and upper limits to this window, but sometimes this is not enough to control the different pressures that the wellbore wall is subjected to. For this reason, geomechanics has become one of the most useful tools to identify and reduce risks for drilling purposes.
It has been proven that increased drilling costs are related in several cases to wellbore instability. Stuck pipe continues to be the most expensive type of drilling-related non-productive time (NPT). If incidents that cause stuck pipe can be reduced, sidetrack risk is reduced. The formation's mechanical behavior due to the stress state and pore pressure alterations encountered while drilling, and the stress-strain relation of the formations exposed in the open hole can indicate a stable or unstable condition.
If the appropriate data is available, different failure criteria can be applied to the formation's mechanical properties, stresses and pore pressure to predict the borehole collapse. A wellbore stability study can identify zones that could increase the probability of a stuck pipe incident. The study integrates the mechanical properties of the rock, formation pressure, the magnitude and orientation of in-situ stresses, and the drilling events observed during drilling, making it possible to reproduce several drilling conditions.
The case presented here is an example of how geomechanics has been integrated into the well planning and execution processes and how geomechanics applied to drilling encompasses more than just the mud weight required to drill a well.