| dc.description.abstract | High-velocity jetting of acid in carbonate formations as a stimulation technique is an emerging technology currently being studied for applications in long horizontal wells. One way to achieve this is by using limited entry liners and nozzles designed to control the placement of acid along the lateral. Previous field-testing has successfully shown desirable acid distribution along an extended reach well with formation heterogeneities. To support the modeling of this stimulation process, seminal laboratory experiments were previously conducted by jetting 15% (by weight) hydrochloric acid (HCl) through limestone cores. Preceding experimental studies showed the formation of bulb-shaped cavities at the jetted surface, and the propagation of wormholes from these cavities. These initial studies revealed that the formation of cavities and wormholes are greatly affected by jetting velocity, interstitial velocity, and permeability.
However, the mechanism of both the cavity formation and wormhole propagation in the core samples still remains unclear. This study aims to better understand these processes by performing acid jetting laboratory experiments with a modified procedure. The new experiments divide acid jetting in multiples stages to produce data snapshots and computed tomography (CT) scan images throughout the cavity and wormhole development in a rock sample. 15% HCl was jetted at constant pressures, with velocities between 107 ft/s and 200 ft/s through six Indiana limestone cores, with permeability measurements ranging from 2.4 mD to 6.9 mD, and porosities around 14%. For each core, multiple jetting stages were conducted until breakthrough stage was reached. Initial interstitial velocity was set at 0.5 cm/min for all cases, which increased to an average of around 1 cm/min around breakthrough point. After each jetting stage, CT scan images and other physical data of the core were obtained before placing it back in the injection setup for the next jetting stage. Injection times for each stage ranged from 1.3 minutes to 4.1 minutes, and each core underwent jetting for three to six stages.
CT scan data of the cores were processed and 3D-rendered, producing high-definition multi-angle snapshots of the rock dissolution progression through time. The results clearly demonstrate that cavities and wormholes develop concurrently during acid jetting. It was observed that rock samples with higher permeabilities form larger cavities, and similarly would create larger cavities at higher injection rates.
These results are of significant use in future experimental and modeling studies of acid jetting, which are needed for upscaling to well stimulation design in the field. | en |
