Production Enhancement Strategy by Combining Ultralong Horizontal Wells with Single-Phase Retarded Acid

Abstract

Abstract In carbonate stimulation and production enhancement, wormhole length is one of critical parameters to increase hydrocarbon recovery from a reservoir. It is well known that wormhole length is a function of the reaction kinetics, acid volume, acid concentration, and acid interstitial velocity. To support longer wormhole propagation especially in low-permeability formations, the stimulation industry has developed retarded acid systems that allow the acid to react with the same strength but delay the speed of reaction so the acid can be pushed farther while consumed to generate longer wormholes. From a well construction perspective, maximizing reservoir contact (MRC) in low-permeability formations increases well productivity. This approach has also been used in UAE to maximize oil production per well and to reduce well count. Record-breaking wells have been drilled in UAE for development and appraisal of low-permeability (less than 2 md) offshore carbonate reservoirs. These record wells have lengths of more than 40,000 ft measured depth and horizontal laterals with more than 25,000 ft of reservoir interval. This paper is going to discuss the application of a retarded acid system in the productivity enhancement of an ultralong MRC lateral. The stimulation design of the ultralong MRC lateral started by evaluating the expected production enhancement with retarded acid in comparison to treatment with normal hydrochloric acid. This was done first by evaluating the production performance of a benchmarked well of similar length and reservoir properties and stimulated via normal hydrochloric acid. Then, by building and validating its production forecast model using nodal analysis, the calibrated model was used to forecast production enhancement utilizing the retarded acid expected skin reduction. The retarded acid system forecasted skin and wormhole lengths were obtained from an acidizing simulator that is tuned to experimentally derived data. A set of key performance indicators related to job execution were designed and monitored such as fluid parameters and pre- and post-stimulation production performance of the retarded acid well. These indicators were used for the retarded acid well model calibration to ensure fair and measurable comparison with the benchmarked well. In the execution phase, data collected from the retarded acid and normal acid stimulations are used for analysis of three objectives which are maximizing production potential from the field using the same volume of acid dosage, improve operation efficiency by volume optimization to get the same production performance, or a combination of the two options. The study is also evaluating the potential enhancement of injectors since they are placed in layers with high volume of dolomite. Many novel technologies were utilized for the successful execution of this study. On the fluids side, dual-retarder on-the-fly mixing retarded acid system has been used. On the job design side, a log-and-completion-based simulator is being used to model the fluid distribution and reaction kinetics to develop wormholes along the ultralong horizontal well lateral. On the lower completion side, a limited entry liner was designed to provide mechanical diversion of acid during bullhead stimulation. On the stimulation conveyance side, a high-volume state-of-the-art stimulation vessel with high pumping rate capability was used to conduct all treatments on the island offshore environment.