Abstract
Conventional acid stimulation has been widely used in carbonate formations. When it comes to horizontal Open Hole environments, this technique has proved to fall behind the challenge of properly distributing the stimulation fluid along the bare lateral section. The non-effective fluid diversion issue is mainly associated with reservoir heterogeneities that are usually encountered in the subsurface such as fractures, permeability variations, reservoir pressure contrasts, to name a few. All this is also the cause for uneven downhole production and injection profiles, producing early breakthrough and sometimes leading to lower sweep efficiency.
ADCO (Abu Dhabi Company for Oil Onshore Operations) has been continuously encouraging implementation of new technologies aiming to maximize the effectiveness of matrix stimulation treatments. Recently, Stim Tunneling was screened for trial in a tight limestone formation in a Giant Oil Field. Stim Tunneling is a selective stimulation technique designed to enhance reservoir-wellbore contact by creating tunnels into the rock through rock dissolution.
Reservoir-A, is an Oil Carbonate Formation currently undergoing a pattern and peripheral injection scheme. The main reservoir consists of several units with subsequence layers exhibiting strong permeability variation ranging from 1 md to 10 md. Presence of fractures have been also confirmed in Bore Hole Image logs. The Stim Tunneling trial was performed in a WAG injector of an inverted 9-spot. The well was selected as a candidate for the stimulation trial seeking increased injectivity and optimized down hole injection profile.
The stimulation job design consisted of creating a series of tunnels distributed along the lateral open hole using 15% HCl acid. The performance of the well after stimulation improved remarkably with Injectivity Index increase 3 times. A case study is discussed in the paper, presenting advantages and limitations of the technology as well as lessons learned derived from the final results.
