Depleted Well Intervention in Extended Laterals Using Coiled Tubing and Commingled Fluid Systems

Abstract

The objective of this paper is to clearly outline the basic principles and techniques required to successfully perform well intervention in wells with low-pressure formations, thief zones, and/or depleted reservoirs—specifically, horizontal or highly deviated wells. The paper aims to review the considerations and provide an example of reliable execution in its most basic form, including simplified calculations designed to be used in conjunction with advanced modeling software available in the industry. Coiled-tubing intervention in lateral wells with fluid-loss potential is inherently high risk. The risk of poor solid suspension or loss of fluid circulation results from the inability to avoid fluid loss and causes costly job failures, lost workstrings or equipment, or reduced well production. For land-based operations in the United States, coiled tubing has been reliably and successfully deployed in depleted and low-reservoir-pressure wells that were unable to support a hydrocarbon or water column to surface. These jobs include sand cleanouts, re-fracture preparation cleanouts, and underbalance millouts in extended laterals. Commingled nitrogen and water-based systems were used to reduce hydrostatic pressures exerted on the reservoir and, thereby, allowed for successful continued circulation. The fluid system was adapted to each well intervention to consider formation type, reservoir fluid composition, job requirements, BHA requirements and limitations, chemical compatibility, cutting suspension potential, and foam integrity. When combined with real-time monitoring of, and response to, well conditions, the occurrence of job failure was greatly reduced.