Technical Paper: Effective Hydraulic Modeling and Field Data for Deepwater Horizontal Well With Low Drilling Margins in Unconsolidated Formation

Society: SPE
Paper Number: 167934
Presentation Date: 2014
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Effective hydraulic modeling to predict the equivalent circulating density (ECD) was highly critical for successful drilling of a pilot well in a deepwater development in the Gulf of Mexico. The drilling objectives included linking three reservoirs, divided by moderately thick shale at relatively high dip while upholding the properties between relatively narrow drilling margins. This difficult drilling environment mandated intensive reservoir drill-in fluid maintenance practices with specific focus on rheology, density, and optimization of bridging materials while reducing the incorporation of acid-insoluble solids.

The pilot, Well B, is one of a handful of horizontals drilled in ultra deepwater shallow BML, having over 2,000 feet lateral, that was successfully drilled in challenging 8,257 feet of deepwater in the Paleogene reserve at a shallow depth of 2,300 feet TVD below the mudline (BML) and the first well to be produced in this reserve development. Due to the shallow depth from the mudline and soft sediments, the drilling margins were extremely low – 0.7 lb/gal (i.e., 250 psi); thus wellbore stability analyses were critical in order to avoid unanticipated losses to formation, losses to mudline, influxes or borehole collapse. Despite the limitations of available offset data used as an analog, the pore pressure and geological fracture gradient were known. However, in comparison to offset Well A (3,800 ft BML) with pressure margins 450 psi, Well B realized a significantly reduced operating pressure window and shallower depth BML. The ECD, equivalent static density (ESD), downhole pressure, and flow rate were carefully monitored to enable drilling within the established operational window and increasing the success of attaining total depth. The meticulous monitoring was a key to the ability to successfully drill the lateral section with only marginal losses and no wellbore stability problems.

The paper presents the hydraulic modeling in addition to the field monitoring data as well as summarize the lessons learned from pilot Well B as compared with offset Well A.

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