Abstract
Operators exploring presalt areas report issues with bottomhole assembly (BHA) wear and failure resulting from factors such as vibrations, stick-slip, and torsional resonance during drilling operations in salt layers. This study presents a new real-time analysis based on geomechanics capability to optimize energy consumption and rate of penetration (ROP) in salt-layer drilling and improve economic results.
A real-time geomechanical analysis based on mechanical specific energy (MSE) was used to optimize drilling and prevent nonproductive time (NPT) when drilling in evaporite intervals. This analysis defined two energy limits as a function of depth. Both maximum and minimum energy limits were calculated in real time based on estimates of confined compressive strength and intrinsic MSE, respectively. The intrinsic MSE calculation depends on the mechanical properties of the rocks [i.e., unconfined compressive strength (UCS), friction angle (θ), and the cutting environment].
When both limits were estimated, a real-time analysis was successfully developed based on measuring and comparing the following:
MSE applied during the drilling process, which depends on drilling parameters, such as ROP, rev/min, weight on bit (WOB), and torque
MSE intrinsic values
Confined compressive strength (CCS) of the evaporate
The analysis identified excessive energy consumption to help reduce and mitigate factors, such as axial/lateral vibrations, stick-slip, torsional resonance, and wear of BHA components in this geological environment. All factors were estimated and analyzed through empirical relations based on logging while drilling (LWD) logs and mud logging parameters.
Results of two case studies show how excess energy results in excessive vibrations and wear of the BHA when this energy analysis is not applied and energy stabilization, ROP efficiency, and mitigated vibrations when the methodology is implemented. A depth versus time plot shows drilling performance optimization with 12 operational days saved and no operational NPT registered. Economic results were also positive.
This study aims to create a methodology that helps optimize the ROP in real time for salt environments based on the estimation of the minimum and the maximum (optimum) values of energy necessary to drill efficiently and avoid BHA failures resulting from excess energy in the drilling system.
