Dynamic Underbalanced Perforating System Increases Productivity and Reduces Costin East Kalimantan Gas Field: A Case Study

摘要

New gas wells at Tunu field in East Kalimantan are normallyrnperforated using the extreme underbalanced (EUB) technique,rnin which a large static pressure differential between thernwellbore and formation, or initial underbalance, is set beforernthe gun is fired. This requires an operation to unload wellborernliquid, a wireline operation to set an anchoring tool, andrnseveral slickline operations to run and retrieve the gun string.rnThe required degree of underbalance depends primarily onrnrock properties such as permeability, porosity, and strength.rnA new approach produces a well dynamic underbalancern(the transient underbalance just after creating the perforationrncavity). By basing the job design on the properties of thernreservoir, wellbore, and gun string, the technique consistentlyrnminimizes perforation damage and thus maximizesrnproductivity. This technique is based on recent single-shotrnperforating experiments that show that it is the maximumrndynamic underbalance—not the initial underbalance—thatrngoverns perforation cleanup. The wellbore pressure was foundrnto vary considerably during the first half-second after therncharges were detonated. This variation in wellbore pressurerncan be manipulated to give a large dynamic underbalance.rnPerforating with the new technique and electric wirelinernwas performed on 10 wells in the field. Software thatrnconsidered wellbore geometry, fluid, gun-string selection, andrnreservoir properties was used to design a specific gun-stringrnconfiguration and to predict the productivity increaserncontributed by the underbalance. The jobs were performedrnsmoothly with significant cost savings compared tornconventional EUB operations and yielded an increasedrnproductivity. Details of the perforating jobs with the newrntechnique will be described, including a cost reduction ofrnapproximately 40% and a significant production increase.rnTesting revealed an average skin value for four wells of -0.29, versus the average skin of 4.73 from 35 conventional EUBrnperforating jobs executed during the multi-year interval fromrn2000 to 2004.