A Step Change in Openhole Gravelpacking Methodology: Drilling-Fluid Design and Filter-Cake Removal Method

摘要

The major trend of completion method in offshore reservoirs with sand control requirement is Horizontal Open Hole Gravel Packing (OHGP). Though gravel packing is a proven method to stabilize the well bore, controlling sand and maximizing productivity, it entraps the filtercake formed by the reservoir drilling fluid. This results in low production rate and consequently leads to the requirement of high drawdown pressure. Hence it is imperative that the filter cake be removed uniformly to ensure lower drawdown pressure, and even flow distribution throughout the producing interval of the well. A review of the completion methodology in poorly sorted unconsolidated sands with high fines content in Brunei also indicates that the situation is not much different from above, demanding to lower production drawdowns while delivering production quotas. The lower drawdown extends the integrity of sand control completion jewelry, reduces water influx, fines migration, and increases recovery factors and reserves. The Brunei Shell Petroleum’s (BSP) Tali asset strategy has been driven towards highly deviated wells with Open Hole Gravel Packs. OHGP requires a high quality mud filter cake to be maintained throughout drilling and placement of the gravel pack. Traditional methods with acid to breakdown filter cake have been proven ineffective as they cause highly conductive wormholes that contribute the majority of production. The acid can also react with sensitive clays in sandstone resulting in secondary and tertiary precipitations. Additionally, acid reacts with the screen metal causing variation in opening tolerances, which is unacceptable for these poorly sorted high fines content sands. The objective of this paper is to present the results of the application of a clean up fluid containing a chelating agent and an enzyme to dissolve the filter cake formed by the drilling mud. Use of enzyme breaker and chelating agent used in the clean up fluid helps to promote the dissolution of starch and calcium carbonate components used in the drilling fluid mud. Laboratory test procedures, results, field case histories and production results are discussed in detail. Laboratory tests include the effect of this cleaning up fluid on the filter cake formed by different drilling mud composition. Field case histories comprise of the gravel packing of the oil producer well and subsequent treatment with the proposed clean up fluid.