Crosslinked Gel Provides Long-Term Control of High-Pressure Gas Well During Coiled-Tubing Fishing: Challenges and Success Story

摘要

Identifying suitable kill fluids to temporarily control prolificoil and gas reservoirs without risk of formation damage hasbeen a challenge within the Niger Delta. Various attempts,particularly in gas wells using conventional brines and gels toenhance well intervention processes normally requirestimulation treatments, in order to bring the wells back toproduction.The engineered cross-linked gel is a temporary blockingformulation used to protect permeable zones from invasion offluids. This system contains a low-residue cellulose-polymerwith a cross-linking agent and can be designed for use with aninternal or external breaker. In general, the use of losscirculation material (LCM) is not recommended because of itstendency to block perforations, complicate fishing operationsand increase the difficulty of clean-up if fishing becomesunsuccessful.This case study is of a gas well drilled and completed for anOperator on the E4.2-reservoir with production capabilityestimated at 8,000 bbl/day of condensate and 150 mmscf/dayof gas. Following the installation of the memory gauges, a 10-hour build-up test of this particular interval was conducted.During the retrieval of the BHP gauges, several incidents leadto three successive fishes getting stucked into the wellbore.The Operator was faced with many challenges: ‘do nothingand produce the well in an unsafe manner at 50% potential',‘attempt a workover' or ‘attempt a coiled tubing riglessintervention', with each option having its attendant limitations.The success in retrieving the multiple fishes was attributed tothe ability to kill the high pressure gas well with a timedependent and acid degradable cross-linked gel system through a high rate bullhead pumping technique. The gel hadlow damage potential to the formation and prevented themigration and fingering of formation gas to the surfacethroughout the fishing operation that lasted for approximatelyone month on 24-hour daily operations. The pre-fishingconduit potential was preserved, indicating that the crosslinkedgel completely got degraded internally at the end of thefishing operation leaving the near wellbore region undamaged.In this paper, the laboratory simulation, features, engineeringdesign, field application and benefits of the engineered crosslinkedgel system are discussed. In addition, the process ofwell killing, specialized coiled tubing and wireline fishingtools and performance evaluation are addressed. The successof the operation includes regain of the original wellperformance, competence in well killing and complex fishing,cost savings and high NPV. Over $2.0 million was savedoperationally with the CT rigless activity when compared to‘workover' or ‘do nothing' options.