Mitigating geomechanical and drilling issues

Pluspetrol Norte S.A. initiated a series of horizontal drilling campaigns in the Yanayacu, Corrientes, Jibarito, and Capahuari fields of the Marañon basin in the northern Peruvian rainforest.

Previously drilled wells encountered considerable geomechanical and drilling problems. Costly sidetracks were common. The average historical NPT per well was 2.2 days. Geomechanical incidents, including stuck pipe, wellbore instability, and tight holes, accounted for a full 97% of NPT in deviated and vertical wells and 69% of NPT in previous horizontal wells. Only five horizontals wells had been drilled before—all with aggressive dogleg severities— using conventional downhole motors that required sliding nearly 100% of the time. Cuttings removal had been inefficient, lowering ROPs. Stationary components had created friction, further reducing ROPs and causing mechanical and differential sticking of the drillstring and packoffs.

Due to changes in reservoir conditions, advances in technology, and new environmental constraints, Pluspetrol decided to implement a fresh approach.

For the data audit, the team compiled, integrated, and analyzed all available data in geology, geophysics, geomechanics, reservoir engineering, and drilling engineering. As part of predrill planning, they performed a geomechanics study, building a 1D mechanical earth model (MEM), which provided a reliable wellbore stability forecast. They analyzed horizontal stress magnitude and orientation, performed trajectory sensitivity analysis, and evaluated potential drilling hazards. Finally, they created a plot from data measured from the DrillMAP drilling planning and management tool to summarize risks and guide preventive measures while drilling. During drilling, a Schlumberger geomechanics specialist compared data from the rig with the predrill forecast to detect deviations and unexpected borehole conditions. After drilling, consultants met with Pluspetrol to document key performance indicators, identify lessons learned, and optimize plans for subsequent wells.

In addition to the multidisciplinary evaluation and support, Schlumberger also recommended replacing traditional downhole motors with a modern rotary steerable system (RSS). Over a 3-year period, Pluspetrol drilled seven successful horizontal wells in the Marañon basin.

Saving time, accelerating ROI, dramatically lowering costs

By establishing best practices in geomechanics and drilling optimization, the company significantly reduced geomechanics-related NPT. The first two wells, for example, had no wellbore instability issues, no stuck pipe, and only moderate tight hole events, which were easily managed at the rig site. In another field, historical NPT that resulted from geomechanicsrelated drilling events dropped from approximately 70% to 15%, or from an average of more than 2 days to less than a day.

Use of the RSS improved drilling performance, required fewer BHAs per well, increased total well length 200–300 meters per well, and increased ROP despite the longer wellbores. Ultimately, Pluspetrol hit its drilling targets 5 to 9 days ahead of schedule, saving rig time, bringing production online sooner, and accelerating return on investment.

As a result, costs were dramatically reduced. Previously, drilling events, fishing, lost in hole events, and sidetracking had cost an estimated USD 2.38 million (sidetracking alone cost USD 2.2 million) per well. With the new approach, Pluspetrol not only eliminated about USD 2.36 million of those costs, but saved an additional USD 420,000 per well by hitting targets ahead of schedule. Net savings: approximately USD 2.78 million per well.