Three novel concepts have been identified which realise the benefits of screenless completions. The most developed of the techniques, the slotted completion for sand management, is described along with the underlying mechanism by which it is able to defer or avoid sand production.
The investigation of this novel completion is based on a laboratory testing programme centred around polyaxial cubical samples of Castlegate sandstone, subjected to a 3-d stress regime. The design of these block tests was based, in part, on numerical analyses, using in-house modelling capabilities for simulating Castlegate sandstone. The analysis assisted in defining the borehole and slot dimensions. The pre-testing numerical analyses are presented, along with the laboratory block test results. Both the analysis and test results provide ‘proof of concept’ for the mechanisms underlying this novel completion technique.
Sand production is a significant consideration when defining a field development strategy for sandstone reservoirs and for completion selection.Sand Production occurs if the stress acting on the near-wellbore region, during production, exceeds the strength of the sandstone formation: This leads to failure and disaggregation of the sandstone, which can then be transported to the surface facilities [1–6]
If sand production is anticipated during the productive life of the well, or field, two generic sand management strategies are available; allowing sand to be produced to the surface facilities, or limiting the sand transport and keeping the majority of the sand and solids downhole, through sand exclusion.
The first approach, sand co-production, has disadvantages resulting from the impact of the sand on the surface facilities. This operation requires additional surface cleaning, separating and disposal capabilities and close attention to monitoring any erosion of the flowlines and facilities . The advantages of co-production include zero or negative completion skins, with increased production, minimal completion costs and more remediation options.
The second approach of downhole sand exclusion, using screens and gravel pack systems, has the disadvantages of relatively high completion costs, positive completion skins initially and which can develop over time due to plugging of screens: this reduces production for given well conditions, e.g. drawdown. Gravel pack completions also impose limitations on the well operations in order to maximise the reliability of the completion. These include slow bean-up, and limitations on the drawdown, or production rate, acting across the completion [8, 9]. Success and reliability of gravel pack systems focuses on the design as well as placement of gravel packing completions: Success requires high quality control on all aspects of the operation. The advantage of successfully deployed sand exclusion technologies is that the volume of solids transported to the surface facilities is limited.
The optimum sand management solution is one where no downhole sand exclusion is required, minimising the risk of plugging, maximising the production and operability of a well, and minimising cost, whilst avoiding sand production to the surface facilities, i.e. screenless completions [10, 11].