Meeting Drilling Challenges in Shallow Extended Reach Wells in a Structurally Complex Field with Heavy Oil and Low Fracture Gradient

Stewart, Gregory L.¹
 Holmes, Gunnar E.¹
 Stockwell, Lee¹
 Levy, Bruno¹
 Kenworthy, Andrew M.¹
 Zambrano, Santiago²
 Van Konijnenburg, Jan-Henk¹

¹BC-10 Development, Shell Brasil E & P Ltda., Barra da Tijuca, Rio de Janeiro, Brazil.
²Drilling and Measurement, Schlumberger, Rio de Janeiro, Brazil.

Shell Brazil is developing a structurally complex Cretaceous heavy oil reservoir in a deepwater,shallow overburden setting, in offshore Brazil. The development plan called for completion of six 600 to 1000m long horizontal producers. Numerous challenges were encountered during development drilling. Integration of subsurface and drilling data was critical in overcoming the challenges.

Challenges encountered during development drilling, depended on the hole section, the formations penetrated, drilling assembles used and individual well path design.

-The shallow nature of the field (900 to 1000 m tvd below mudline) resulted in the need to start the build-up section near mud line.

-The 12 1/4” build-up section was drilled with Synthetic Based Mud (SBM). Induced fracturing, opening of minimum stress faults and the presence of high perm sands resulted in substantial SBM loss.

-The high net to gross (NtG) reservoir model predicted from the vertical well control, and the need for gravel pack sand control, lead to a completion interval design with a straight near horizontal well path.

As problems were identified, the subsurface team worked with the well engineers and directional drillers to optimize drilling parameters through the integration of drilling and subsurface data. As a result of the collaboration, many aspects of the drilling program were updated to improve drilling performance and well placement.

3D and 2D displays of seismic, with structural data, well bore lithology, and drilling data such as steering ratio, build rates, ROP and WOB were used to better understand the relationship between geological formations and drilling behavior. Understanding the drilling behavior of specific formations and lithologies at various depths helped in the re-design of BHA’s, refinement of the steering program, and updating LWD requirements.

Mud weights were reduced, drilling fluids modified, BHA’s and LWD tools changed to meet the drilling challenges. Recommendations for subsurface data collection from appraisal and development wells in order to reduce uncertainties and improve the drilling program were formulated. Even the basic well design and drilling philosophy was updated to include geo-steering in the reservoir and additional pilot wells in some areas of the field. Collaboration of subsurface and drilling teams lead to significantly improved drilling performance and well placement.