Limited-Entry-Liner Well Stimulated Effectively With a Viscoelastic Diverter-Acid System

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213785, “Effective Stimulation of a Limited-Entry-Liner Well Using a Leading Viscoelastic Diverter-Acid System,” by Timothy I. Morrow, SPE, and Ahmed M. Fawzy, ADNOC, and Abraham Ryan, SPE, SLB, et al. The paper has not been peer reviewed. A horizontal water-injection well with a limited-entry-liner (LEL) completion in an onshore Middle East carbonate reservoir was stimulated with hydrochloric acid (HCl) using a large volume of a viscoelastic diverter-acid (VEDA) fluid system ahead of the main acid stage. The VEDA stage was needed to deliver sufficient acid volumes to the toe of the well, resulting in a significant increase to the injectivity index and more-even distribution of injected water across the horizontal drain. The LEL is a lower completion type designed for openhole wells. It consists of an array of small, unevenly spaced holes placed along a string of blank pipes. Swell packers typically are placed along the LEL completion to divide the lateral into compartments. The size of the LEL holes usually is in the range of 3–6 mm. The LEL completion provides the capability to perform acid stimulation by bullheading at high pumping rates, and the distribution of the holes serves to provide a type of mechanical diversion of the stimulation fluids. A simplified schematic of the LEL concept is shown in Fig. 1. The properties of the LEL used in this study include the following: - Hole spacing broadly is within the design range of 40–60 ft - Average compartment length is within the design range of 500–1,000 ft - A significant permeability contrast exists between the heel (Aones 1 and 2) and the toe (Aones 4 and 5). The total injection interval for this well is 4,075 ft. Because of the large permeability contrast between the heel and toe, however, it is possible that a bullhead acid stimulation may result in a relatively small volume of acid entering the toe compartments. The acid stimulation for this well consisted of 42 gal/ft of 15% HCl to be pumped at the maximum allowable rate. Acid stimulation treatment modeling was performed for the following three scenarios: - A hypothetical scenario of 15% HCl pumped into an openhole completion - The baseline scenario of 15% HCl without any VEDA stages pumped into the LEL - An alternate scenario in which a VEDA stage is added to the beginning of the acid package and pumped into the LEL The purpose of modeling the hypothetical scenario was to illustrate the mechanical diversion provided by the LEL. For a hypothetical openhole completion, a bullhead acid stimulation at maximum allowable pumping rate was predicted to place very little acid into Zone 5 at the toe of the well. Conversely, the higher-permeability heel Zones 1 and 2 would take most of the acid (approximately 80%), with Zones 3 and 4 receiving just 20%. By comparing the simulation results between Scenario 1 and Scenario 2, the mechanical diversion effect of the LEL completion could be estimated. After adding the LEL configuration to the stimulation model, the model was calibrated with production-logging-tool (PLT) data acquired from the well during the prestimulation injection period.