Dynamic Acid Placement Technique (DAPT) Improved Stimulation of Long Open Hole Tight Carbonate Reservoir
Authors: Abbad Bilal , Pathak Himanshu , Almutawea Yusuf , Alaskari Nasser , Engineer Yusuf , Malik Mohammed , AlDosseri Ahmed 
Published: February 2024

The main objective of matrix acidization treatment is to get homogeneous invasion and distribution of stimulation fluid over the entire production interval. When acid is pumped without mechanical or chemical means of controlling its distribution, it naturally tends to flow into the highest permeability zone, defeating the objective. This paper describes techniques, application, and lessons learned in carbonate acidizing through dynamic acid placement technique which doesn't requires any other mechanical or chemical mode of diversion.

Ball-sealers, foams, high-viscous pills and mechanical tools are amongst frequently used diversion methods. Whereas dynamic acid placement technique works on Bernoulli's principal where homogeneous acid invasion is achieved by jetting acid into open hole section at very high velocity. This phenomenon creates larger entry points at point of placement and creates insitu vacuum near injection point, resulting in acid treatment keep getting placed at point of injection and not leaking off in high permeable section. By combining identification of Sweet-spots, right additives, pumping schedule and dynamic placement technique the objective to form homogeneous and deepest penetrating wormholes could be achieved.

Detailed stimulation modeling, considering various application methods, such as bull-heading or injection by coiled tubing, at different rates, acid concentrations, and acid loading points of placement helped to validate the process. A combination of detailed study of candidate wells, identification of optimum treatment intervals, point of injection, customized pumping schedule and selection required acid additives and dynamic placement technique resulted operator in Bahrain to achieve maximum zonal coverage, radial penetration, reduction in skin, and deeper wormholes.

Mechanical diversion has limitation in wells having smaller production tubing and is relatively expensive as it requires special equipment. On other hand and chemical diversion can be placed in any type of completion but can still be very expansive and doesn't offers accuracy of placement and are not as efficient as mechanical means are; The dynamic placement technique requires relatively simpler tool that can be run on Coiled Tubing or jointed tubing through smaller production tubing and can direct the flow at the point of interest overcoming the shortfalls of mechanical and chemicals means of diversion resulting with an optimized solution for producing zones with nonuniform permeabilities and uneven damage distribution.

The best practices described in the paper resulting deeper acid penetration and homogeneous distribution over production intervals & significant reduction in skin, could be applied in similar applications. These best practices will help achieving best outcome from carbonate acidizing introducing dynamic acid placement by overcoming the limitations of other used mechanical and chemical diversion technique. It also opens the possibility of getting even better results by combining dynamic placement with mechanical and/or chemical diversion techniques.