Techniques for Managing Embedded Shales in Long Open Hole Laterals with Sand Control Completions

Abstract

A review of lower completion operations in Begonia development in offshore Angola. This work covers completion selection and analysis of open hole gravel pack operations in long horizontal wellbores with interspaced sands and shales. Development wells have been drilled and completed in the Begonia development with 9.5″ openhole sections ranging from 500m to 850m in drainage. The formation is characterized with clean unconsolidated sands interbed with shale sections. During drilling and lower completion operations hole stability is maintained with mud weights significantly more than reservoir pressure, in addition to the inclusions of solids within the drilling fluids to ensure filter cake stability. To increase the success of sand placement several lower completion tools were deployed that include shunted screens, open hole packers, interspaced blank sections and diverter valves. Open hole gravel pack (OHGP) operations were carried out using traditional pumping equipment with a Xanthan based gravel pack fluid that achieved the required viscosity and sand suspension properties to ensure successful gravel placement. Reservoir drilling fluid was an oil based inverted system with solid suspension, this was enhanced with a dedicated screen running fluid with high fluid quality specification to reduce the chances of screen plugging. All wells were successfully drilled and completed with a sand control lower completion design, deploying alternative path screens. Each of the wells achieved a 100% pack, however none of the wells exhibited a conventional screen out with zero pump rate as often found in sand control operations. Here confirmation of screen packing was carried out using analysis of bottom hole memory gauges on the wash pipes. To maintain shale stability during pumping operations a combination of open hole packers, blank sections and diverter valves were employed to force sand bridging and subsequent shunting at key intervals in the wellbore. Placement of these sand control tools was confirmed with the use of sand control placement simulator and investigation of open hole logs. This strategy prevented the release of shales into the gravel pack fluid that would have resulted in high completion skins on well testing. Due to these factors each well was able to achieve production targets will final skin of less than 6. Extended reach wellbores can be drilled with horizontal sections far exceeding traditional norms with sand control applications in mind. However, with the increase in drilling length also increases the probability of completing wells with multiple sand bodies or interbed shales. Previously these shale sections have been gravel packed or well length truncated to avoid gravel packing where destabilization of shales can cause challenges to well completion or compromise well production. This work has demonstrated a number of completions, drilling fluid and OHGP techniques that allow for successful gravel packing in these conditions.