Abstract

There has been a considerable number of matrix acid stimulation treatments performed in high porosity – low permeability chalk reservoirs in the Danish part of North Sea over the last four decades. During this time, several acid types and diversion techniques have been employed to obtain a desired fluid distribution without the ability to measure the actual success of this distribution. The typical references to design such treatments were based on the knowledge of carbonate dissolution reaction by acid, lab scale core testing and reference outputs of matrix acid model simulators 1 . Limited work has been carried out to capture actual dissolution behavior and distribution down the well. This includes understanding both acid-diversion efficiency and production contribution for complex and extended reach intervals.

The implementation of Distributed Temperature Sensing (DTS) and Zonal Downhole Gauges as part of the lower completion in one complex, newly drilled well, has enabled the possibility of monitoring real time temperature profiles along the wellbore allowing determination of flow distribution both before and after an acid and diverter stage enters the formation 2 . Realizing the effects of acid and diverters will lead to a better understanding of the chemistry, reaction and diversion process, and subsequently to the optimization of future designs. Fluid flow path and zonal isolation was also monitored during the treatment which provided insights into mechanical issues with respect to tubing, packer, cement and wellbore integrity. In addition to the real-time data gathered during the execution of the treatment, considerable knowledge of post stimulation zonal production contribution was afforded for both production and stimulation modeling.

This paper discusses the benefits, challenges, execution and findings of a complicated application of both DTS and zonal gauges for matrix acidizing treatments and production characterization on an Ekofisk chalk formation. The primary stimulation and the subsequent re-stimulation was executed in opposite ends of the perforated interval with DTS being recorded prior to and after the stimulation fluid was pumped. The captured lessons learned will be an invaluable reference for future acid stimulation treatments of Danish chalk in the North Sea.

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