Advances in Dendritic Acidizing Reveal Light at the End of the Tunnel
Authors: Wilson Adam 
Published: June 2018

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper SPE 189945, “Dendritic Acidizing Update: The Light at the End of the Tunnel,” by C. Dean Wehunt, SPE, Stefan K.K. Lattimer, SPE, and Darren R. McDuff, SPE, Chevron, prepared for the 2018 SPE/ICoTA Coiled Tubing and Well Intervention Conference and Exhibition, The Woodlands, Texas, USA, 27–28 March. The paper has not been peer reviewed.

Dendritic acidizing (DA) has a long history in the oil industry, going back at least to the 1980s. Significant technical advances include single-trip multitunnels using only acid-pumping equipment and a coiled-tubing (CT) unit, simultaneous tunnel creation, and improved parameter modeling and optimization. This paper provides an update on recent advances for DA methods, also known as acid tunneling, presenting a comprehensive review of published information for three different tunneling methods.

Introduction

A well with multibranching major tunnels and a superimposed structure of wormholes emanating from the main tunnels has been called a dendritic well. This paper refers to methods that include the use of acids to construct such a well as DA. DA methods can be thought of as a hybrid between multilateral wells with many short branches with low skin factors and matrix acid jobs with very long primary wormholes and many branching wormholes from the primary wormholes. A conceptual example of a horizontal well section with formation tunneling and DA with branching wormholes adjacent to the primary tunnels is shown in Fig. 1.

Many different methods are used to form small-diameter lateral branches from a parent wellbore. The methods are differentiated by characteristics such as requirements for workover rigs, CT rigs, and deflector shoes for tunnel initiation; acid use in the process; and primary tunnel creation method. 

Method A

Method A uses a proprietary small-diameter CT unit to deploy a jet nozzle on a flexible, retractable hydraulic hose. The method uses mechanical energy to blast the formation during tunnel creation and, in some cases, also uses acid either while jetting or while retrieving the jetting nozzle to chemically assist with tunnel creation and reduce the skin factor adjacent to the formation tunnels.

Method A can be applied in either openhole (OH) or cased-hole completions. In cased-hole applications, a deflection shoe must be run on a work string using a conventional workover rig, and then a hole must be cut in the casing with a separate milling tool. After the milling tool is retrieved by the proprietary CT unit, the jetting nozzle begins jetting a tunnel perpendicular to the well. Although the milling step is not required for OH applications, the deflection shoe must still be used. The jetting nozzle is deployed on a flexible tool that is kept perpendicular to the well by tension on the hose. The tension is also what pulls the hose into the tunnel, so Method A is a pull-the-nozzle method. Hose tension is created because there are rearward-discharging jets with greater discharge area than the erosional jet discharging toward the tunnel tip.