Integrated Approach to Drill Curve and Vertical Sections Across Multiple Porous Unstable Carbonate Formations with Superior Borehole Quality for Multi-Stage Fracking Completions in Deep Gas Wells
Authors: Ponomareva Daria , Corona Mauricio , Franco Nata , Ahmed Sajjad , AlAwfi Mohammed 
Published: February 2022

This paper will present the integrated approach taken to ensure high wellbore quality delivered across the reservoir sections while drilling in deep vertical gas wells to successfully run and set multi-stage fracking (MSF) completion or cemented liner. It also covers the integrated approach to drilling the curve section in horizontal wells to ensure well objectives will be met when drilling horizontal holes across the reservoir.

The gas field is characterized by a high level of lithological and geological heterogeneity, productions zones in such deep wells (more than 13,000 ft True Vertical Depth (TVD)) with different pore pressure had to be combined in the same section some cases due to well design limitations and production objectives. Applying industry-standard overbalance pressure while drilling is not enough to keep the wellbore stable and create a gauge borehole; therefore, an integrated approach was implemented in the planning and execution stages. As a result, it allowed combining depleted and charged production zones in the same section with a maximum of 4-5 Pounds Per Gallon (PPG) Equivalent Mud Weight (EMW) difference in pore pressure and keep the wellbore stable. This difference in overbalance is still manageable in vertical holes. However, the results can be very challenging in high inclination intervals.

Drilling the build-up/landing portion in horizontal wells can be very challenging from the directional work perspective. The landing of this production liner needs to cover most of the caprock as this is the key to avoiding any disturbance on the borehole while drilling the horizontal section below the previous liner shoe across the unstable cap rock. The proper selection of the mud weight requires geomechanics and structural models to anticipate any rock failure. Landing the previous production liner at the planned inclination will help to reduce the directional work amount left in the horizontal section. Any directional work in the horizontal section is limited to 1 deg/100 ft Dog Leg Severity (DLS). Based on the field experience, DLS bigger than 1 deg/100ft will complicate the deployment of the lower completion string, either MSF or Cemented Liner.

From the operational point of view, the building angle in the build-up/landing section is limited by the power transmitted from the surface to the downhole tools, rotation, and hydraulic power. Also, the selection of the directional tools is the key for performance; the wrong selection of the directional tool can compromise the directional work due to hydraulic power limitation that can be applied.

Last but not least, the high overbalance environment (2000-4000 psi) in the build-up/landing section plus the lithological heterogeneity and interbedded formations represent additional risks that should not be ignored, such as downhole mud losses and stuck pipe incidents. Combined expertise and project experience enabled an integrated approach while planning and executing these challenging wells. The proper geomechanical study, Bottom Hole Assembly configuration, bit selection, fluid bridging strategy, directional work distribution, and selection and control of drilling parameters together allowed achieving main targets in deep gas wells in the Middle East.