Optimizations and Tubular Practice from Integrated Packer Stress Analyses during High-Rate, Multiple Acid Jobs in Low-Permeability, HPHT Reservoirs, China

摘要

This paper presents various case studies that were performed on an HPHT gas well located in the TarimrnBasin, China, with a primary focus on well completion, string design, and technique in response tornpacker-seal failure resulting from the interconnection of production casing pressure when conductingrnstaged acid jobs with a straddle-packer string. After tripping out, it was discovered that the upper packerrnmandrel was broken. This paper discusses the factors that led to the broken mandrel and packer-sealrnfailure and provides a unique solution to these challenges during staged acid jobs.rnBased on a detailed investigation conducted at the scene and further post-mortem studies using anrnadvanced wellbore temperature simulator that integrates with tubing and packer-stress analyses, it isrnbelieved that acid jobs using a heavy-duty pump under high pump pressures have resulted in a rapidrntemperature drop inside the wellbore, causing possible liquid contraction within the enclosed spacernbetween the straddle packers and, subsequently, decreasing the pressure. High differential pressurernbetween the upper and lower packer, as well as inside and outside of the enclosed space, can lead to arnbroken mandrel and packer-seal failure.rnThis paper discusses the failures that were analyzed using a comprehensive model that integrates withrntubing and packer-stress analyses by implementing multiple iterations and conditions with variations inrnpressure that were established between the packers during acid jobs. In addition, the string mechanicalanalysisrnmethod was used for the staged acid jobs. Based on case studies on the different methods forrnmitigating string challenges, a method was selected as the primary measure for improving string safetyrnduring staged acid jobs for high-pressure wells, which has been successfully applied in staged acid-jobrnoperations for two wells in this field.rnVarious models for tubing and packer mechanical analysis for staged acid jobs were established,rnproviding a better understanding of pressure with change in temperature within the enclosed spacernbetween packers. The results were able to explain the causes of packer failure from the string mechanicalrnpoint of view, which identifies the effect of various parameters on pressures within the enclosed space andrnthe effect of pressure change to the packer and tubing stresses. The results were supported by a detailedrninvestigation conducted at the wellsite.rnThe thesis of this paper introduces various methods for improving the safety of packers and strings,rnincluding increasing the temperature of injected fluid, tapping on the string between packers, andrnoptimizing string design. Based on analysis and field study, tapping on the string between packers hasrnbeen the best measure for improving string safety during staged acid jobs for high-pressure wells in thisrnfield.