First Application of Multistage Pinpoint Acidizing with Limited-Entry Liner in a Record-Breaking Ultra-Long Openhole Horizontal Well in Central Iraq

Abstract

A record-breaking 3,553-m openhole horizontal well drilled in a carbonate reservoir in central Iraq posed significant intervention challenges. Extreme length caused excessive friction during coiled tubing (CT) run-in to total depth, while heterogeneous and low-permeability formations led to uneven stimulation and unstable production. A new stimulation and completion strategy was documented in this paper to enable full-depth CT access and effective wellbore-wide stimulation. The proposed solution integrates two complementary technologies. First, a partial limited entry liner (LEL) was suspended at the heel to reduce CT friction, regulate acid intensity, and balance inflow during production. Liner length, perforation density, and hole diameter were systematically optimized through coupled tubing-flow friction analysis and acid wormhole propagation modeling to ensure both safe CT access to total depth and uniform stimulation distribution. Second, a geology–reservoir–engineering integrated workflow was implemented to design multistage sand-jetting acidizing, optimize stage spacing, jetting intensity, and acid volumes. Sand jetting was used to initiate artificial fractures for deep reservoir connectivity, while subsequent acidizing generated wormhole networks to expand the stimulation volume in three dimensions. A toe-to-heel pull-back acidizing sequence was further applied to remove near-wellbore damage along the openhole wall, enabling full-length volumetric stimulation of the ultra-long horizontal section. Following close integration of simulation and field operation, a 1,480-m, 4.5-in perforated liner was successfully deployed to the planned depth, eliminating CT run-in risk and enabling 100% wellbore contribution. Based on limited-entry and acid placement optimization, perforation density was increased from 10 to 25 holes per meter with a 6-mm diameter, and a total of 1,500 m³ of acid was placed using sand-jetting, pinpoint acidizing, and a toe-to-heel pull-back sequence in a single trip. Diagnostic data confirmed that 23 distinct stimulation zones (Fiber optic logging), 3.5m average fracture penetration (Pressure matching), and wormhole density increase from 5/cm² to 20/cm². Post-treatment well testing yielded 10,647 bbl/d ~5× higher than conventional acidizing benchmarks. The operation achieved a 70%-time reduction compared with conventional ECP methods, zero CT stuck incidents, and USD 2.0 MM cost savings versus cased-hole completion, with stable production maintained over 90 days. This paper demonstrates a field-proven stimulation technology that achieves 100% wellbore contribution in an ultra-long openhole horizontal well through the integration of partial limited-entry liner completion, sand-jetting, and acidizing. It provides a technical solution for the low-permeability and complex lithology carbonate reservoirs in Middle East.