Low-Cost Selective Perforation Provides Long-Term Sand Control, Sustainable Production and Low Carbon Footprint in Marginal Asset Offshore Malaysia

This paper presents an innovative approach on sand management through low-cost selective perforation providing long term sand control with sustainable production in marginal asset offshore Malaysia. Sand production is a prominent threat in the offshore oil fields in Malaysia. For Field S, existing wells are completed with a cased hole gravel pack for multilayer completion which is a costly capital expenditure. As part of EOR GASWAG infill development campaign for seven wells in 2016, detailed analysis was conducted to identify and selectively perforate competent sections while still delivering successful production target from the whole project. After more than 8 years, we revisit the decision and result from the successful selective perforation completion strategy. In target reservoirs with varying rock mechanical properties and sand production risk, selective perforation method was chosen. Geomechanical modelling was conducted using conventional core data from exploration and appraisal wells, and petrophysical logs of other development wells close to proposed target wells. Synthetic predicted open hole logs for the infill wells were generated with compressive strength and water cut sensitivities to determine best perforation intervals based on critical draw down estimated with varying reservoir pressure. This approach is used in real-time during drilling operation when open hole log data became available, model became further tuned and recommendations to improve completion strategy were communicated with completion and subsurface teams. This on-site advice which was made available immediately after each well drilling helped further tune the perforation interval selections and avoid perforating weaker intervals which were more prone to sanding. This perforation interval adjustment was looked in combination with quick look petrophysical evaluation and pay zone interval identification. Among the sensitivities performed with the model were perforation tunnels size, orientation, sand free envelopes and decreasing reservoir pressure to understand safe drawdown. After 8 years in production, the subject wells still in production without sand production which proved the selective perforation approach is indeed the low-cost and effective sand control for this type of well and rock properties and provided low carbon footprint with significantly less rig operation time, costs, and material consumption, compared to previous cased hole gravel pack method. In this Field S, the typical completion type has been gravel pack for many years. Different strategies used in sand control method where in this case selective perforation implemented for the first time in the field. Even with all diligence in project assurance, there was always some level of uncertainty. But the team has taken a bold decision for it and so far, sustainability in oil production and sand control has been maintained for the last 8 years. Capex has been significantly reduced by about USD 14 mil from 7 wells. Oil production target was achieved long term without sand production. Significant reductions in GHG emission and carbon footprint have achieved at estimated 40 tonnes CO2e from all the wells.