With water production continuing to increase from mature reservoirs and the need to enhance hydrocarbon recovery from these reservoirs economically using existing wellbores, the requirement for innovative thru-tubing zonal isolation solutions has never been greater. Due to the complexity of the completion design and reservoir in mature fields, the benefits of high-expansion plugging devices and coiled tubing conveyance for chemical placement have become increasingly important.
Thru-tubing inflatable technology has, for some time now, been providing high-expansion devices to pass through the existing completion and isolate in the liner or casing below. However, as reservoirs deplete and remedial work such as re-perforation is performed, the conditions in which these tools are required to perform are becoming ever more challenging.
This paper will focus on two coiled tubing water shutoff interventions using thru-tubing inflatable technology in conjunction with cement or chemical placement. In these interventions, the wellbore conditions were considered particularly challenging - sub-hydrostatic bottomhole pressure, multiple perforated intervals and an existing zonal isolation device in the form of a straddle. These case histories will be examined in detail, with emphasis on the pre-job planning, equipment selection, operational procedures, lessons learnt and post job results.
In order to maximize the chances of success of a thru-tubing inflatable water shutoff intervention, it is imperative to properly plan the intervention. The following key aspects of the planning phase have been identified and should always be given full consideration:
Gathering of complete and accurate wellbore information
Full understanding of equipment limitations to ensure operating envelopes are not exceeded
Preparation of the wellbore prior to thru-tubing inflatable intervention
In order to facilitate the pre-job planning process, a number of initiatives have been developed and are used to ensure that the aforementioned key aspects are fully addressed. These initiatives have been discussed more fully in SPE 54476 - "Through Tubing Inflatables: Isolation Planning and Guidelines for Coiled-Tubing Applications" and some are listed below:
Client intervention planning guidelines
Structured interface document for recording of well bore information
Use of memory pressure/temperature gauges in drift runs
Engineering analysis aided by software and performance envelope
Increased global communication via webcasting technique
Problem solving/risk matrix for mitigation of risks to success of intervention
This paper will provide a detailed analysis of two particularly challenging thru-tubing inflatable water shutoff isolations, and will demonstrate how several of the aforementioned initiatives were used to maximize the chances of success of the interventions.