The Reinvention of a Well-Established Coiled Tubing Intervention Workflow Creates New Perspectives for Acidizing Openhole Horizontal Tight Carbonate Water Injectors
Authors: Punnapala Sameer , Berrahmoun Hocine , Al Nuimi Saber Mubarak , Slamet Mohammad , Radwan El Sayed , Molero Nestor , Ali Khan Rao Shafin , Mhiri Adnene , Ramondenc Pierre , Belkadi Wafaa , ElAttar Ahmed 
Published: November 2020

Abstract
Reservoir heterogeneity, presence of faults, lower coiled tubing (CT) injection rates, precise fluid placement, and uncertainty of downhole dynamics are the major challenges for matrix stimulation of openhole horizontal water injector wells completed across tight carbonate reservoirs in the onshore Middle East. The stimulation strategy implemented over the past decade to address those challenges was deemed ineffective, often leading to a rapid decline in injection rates after the treatments and, therefore, frequent restimulation.
Since 2019, a different intervention approach has been implemented, leveraging a workflow based on CT equipped with fiber optics for real-time downhole telemetry and distributed temperature sensing (DTS). Results to date have been encouraging, yielding significant injectivity gains along initial trials. The workflow recently evolved with the inclusion of petrophysics and seismic data during candidate validation to determine a baseline zonation of the openhole section. This critical new step in the stimulation strategy is made necessary by the presence of faults or high-conductivity streaks, whose presence require additional engineering of the fluid placement to avoid early water breakthrough in the producers.
During job execution, after the wellbore has been conditioned using a high-pressure rotary jetting tool, DTS surveying is conducted to confirm the conductivity of faults crossing the uncased section and determine the distribution of high- and low-intake sections along the open hole. Adjustment to the pumping sequence—including zonal coverage, volumes, and diversion techniques—are decided based on that information. The prestimulation injection profile, together with petrophysics and seismic data, enables segmenting the open hole into intervals requiring different levels of stimulation, so each section can benefit from a customized treatment that increases injectivity and improves uniformity of injection. Complementary fluid placement techniques and diversion requirements, such as dual injection, are also identified at this stage and generally determined by the level of conductivity of the fault system detected with DTS. During the stimulation stage, fiber-optic telemetry is used to optimize jetting pressure and monitor downhole pressure in real time to ensure fracture pressure is not exceeded. Upon completion of the acidizing stage, another DTS acquisition is conducted to assess the poststimulation injection profile. The workflow enables incremental assessments through the course of the operation, adding flexibility to the operational sequence and the possibility to repeat steps when the expected injectivity gains are not achieved, or a new segmentation of the open hole is required.
This reinvention of the matrix stimulation workflow brings new perspectives for acidizing openhole horizontal tight carbonate water injectors featuring highly conductive streaks or faults. Using this methodology can significantly improve results over conventional practices more than twofold based on initial results. It is particularly adapted to wells where reservoir heterogeneities lead to nonuniform injection profiles and the risk to unbalance pressure support in the formation.