| Popis: |
New energy demands are pushing the petroleum industry to drill more shale formations. At the same time, the shale slow drilling rate at depth convinces us that there is a need for serious attention to this field, namely finding a way first to understand the causality and then to resolve the bit balling issue associated with slow shale drilling. For this reason the industry has always been interested in finding viable solutions to mitigate "bit balling" as a main source of shale slow drilling rate. In this work we try by various means to understand the shale slow drilling issues. Rosebank is one such field located in the west of Shetland, North Sea. This field encounters slow drilling rate at great depths. The authors studied the aforementioned field to investigate different shale chemo-physical parameters affecting drilling rate and most importantly, those which adversely affect drilling performance. These parameters comprise (1) shale chemo-physical constituents and (2) operational drilling parameters. For finding a cause and effect relationship between (1) and (2) and characterizing the shale we carried out extensive Elemental Oxide analysis using Energy Dispersive Xray (EDX), Xray Diffraction (XRD) to identify and understand relationship between the shale-clays structural formula Non Performance Factor intervals. What guided us to these relationships were the chemical reasons for shale Water Retention which addresses part (1) and devise a theoretically sound model (HDPP) to pinpoint troublesome shale sections and for addressing the shale slow drilling issue in part (2) above. The results show a clear cause and effect relationship between (1) the shale chemo-physical constituents and (2) poor shale drilling at depth where the bit records indicate inefficient Drilling Performance Parameter. Specifically, we have pinpointed the depth where the increase in the shale Iron and Water content match the onset of poor drilling and the necessary sidetracking the well for the prospect under study. We concluded that shale water retention is due to the hydration property of Iron and Sodium especially when the ratio of Iron / Sodium becomes very high. This high ratio is also found where the ratio of Smectite / Illite and the shale water content is high as well. Obviously these high values do not permit the shale to completely expel water under the Compaction- Consolidation stresses at depth and that shale water retention renders it plastic, bit-balling shale. The benefit our work to industry is imbedded in our trouble shooting methodology for this particular prospect. Specifically, assuming all mud plan and treatments and the choices of selecting drilling parameters are made properly, we recommend the Iron control additives be a part of mud formulation for this prospect to mitigate further activation of shale stickiness and balling effect. |
